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MG MGB Technical S.A.E. 7/16 Set Screws to Blank Off Air Ports BBS discussion at MG-Cars.net
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MG MGB Technical - S.A.E. 7/16 Set Screws to Blank Off Air Ports
| Does anyone know where you can find (in the U.S.) the 7/16 S.A.E. allen set screws to block off the air ports on the Gk series and other cylinder heads. Thanks, Jeff |
| J Delk |
| Any good hardware store, if you can find one. It is standard for certain sizes of keyway equipped pulleys and shafts. Farm/tractor/truck suppliers, or good auto parts, same caveat. McMaster-Carr or MSC online in boxes. Failng those, cut off some 7/16 SAE bolts and slot with a hacksaw. FRM |
| FR Millmore |
| What I am finding is that they carry "fine" and "course" thread set screws - I am looking for the Allen Head type. Noe seem to use the S.A.E. designation and most don't even know what that is - this is even the case at industrial supply type places. |
| J Delk |
| Morons! People in the business should be able to tell you that SAE is the standard for fine thread bolts in the US. These dopes no doubt live where they work, since they are evidently too stupid to find their way home and back again, never mind figuring out how to open the door. It is UNF (Unified National Fine)in UK, and is a standard designed to ensure interchangeability between US and English made threads with Pitches and thread forms matching the two standards used in USA. UNC (Unified National Coarse) is the corresponding coarse thread, and is to interchange with USS or United States Standard. For 7/16 diameter, the SAE/UNF/Fine thread is 20 TPI (threads per inch). FRM |
| FR Millmore |
| I got mine from McMaster-Carr. Bought a box of 25 and shared them with fellow B enthusiasts. |
| Greg Bowman |
| Jeff- Here's where I have to buck the crowd, so to speak. Use 7/16"-20 UNF fine-threaded iron bolts 3/4" in length. Do not be tempted to use steel Allen head plugs because they will have to be bottomed out into the cylinder head in order for their threads to create an effective seal. Should a casting defect be present, the resulting stress stemming from the different coefficients of expansion of that of the steel of the Allen-headed plug and that of the cast iron of the cylinder head can result in cracks forming between the walls of the exhaust ports and those of the coolant passages adjacent to where the plug is seated. This does not occur when the steel injector plugs are seated in place because, being hollow, the steel of which they are fabricated can expand inwards and thus not place any stress upon the material of the cylinder head. Should cracking occur, when the engine is running the cooling system will be pressurized by the venting exhaust gases, leading to leaks at the hose junctures, vapor lock inside the cooling system, and, in some cases, a blown cylinder head gasket. When the engine is not running and the exhaust valve is closed, coolant will puddle atop the exhaust valve as well as leak into the exhaust system. If the exhaust valve is open, the coolant will enter the combustion chamber and trickle down into the crankcase, polluting the oil. Now, before we're beseiged with a storm of postings from a vast multitude noisily proclaiming that they've been running their engines with steel allen-headed plugs in place and have had no such problems develop, allow me to state that such casting defects are not the norm, but, you never can be too careful........ |
| Steve S. |
| Good point Steve, something a lot of us have not thought about. Fletcher - "These dopes no doubt live where they work, since they are evidently too stupid to find their way home and back again, never mind figuring out how to open the door. Sounds like the last person I asked a queston of in Lowes (or was it agent orange?), they are certainly not hired for their intelligence. Cheers - Dave |
| David DuBois |
| ".........they are certainly not hired for their intelligence." When you pay peanuts, you get monkeys. TTFN |
| Derek Nicholson |
| I am truly sorry, but I find Steve's worry to be perhaps the most arcane bit of theoretical fearmongering I've ever met, and I used to sit up til dawn with friends conjuring such scenarios as a matter of amusement. Are we to also fret about the same thing because of steel studs holding the manifolds to the head? Iron bolts?? The last "iron" bolt was probably made c1850, and it sure wasn't fine thread. There is virtually no such thing as "iron" in commerce, and if there were its coefficient of expansion would be likely near that of steel, since anything other than lab grade iron has enough carbon to be classed as mild (or low carbon) steel. In fact "iron" is rare enough, and the definitions subtle enough, that I can't find a coefficient for "iron". Coefficients are given as n x 10 (to the -6) "(change of dimension)/"(length)/degreeF(change) in the english system. Machinery's handbook gives n = 6.55 for cast iron, 6.61 for wrought iron, 6.33 for carbon steel. Other references give gray cast iron as 6, and most carbon steels as around 8. Precise alloys and heat treatment also affect the coefficient. When my daughter built her differential expansion thermometer for her 7th grade science fair, it was experimentally determined that hardening a piece of high carbon tool steel raised the coefficient a bit from the annealed state, a figure that was slightly lower than mild steel; this experiment revealed that the Machinery's HBK data are more correct than the other source (Machine Design Materials selector guide). That would put the coefficient for hardened high carbon steel near 7, possibly representative of the screw. Taking a reasonably extreme case of CI being 6, and "steel" being 8 the total difference in expansion can be calculated. The differential coefficient of expansion will be 8 - 6, or 2; the maximum dimension involved is the screw diameter of .4375, as the standard setscrew is 3/8 long (the change in length will be less than the dia change). If you put the screws in on a cold day, say 12degF, and heat the engine to boiling, the temp change is 200degF. So, 2x.4375x200=175 times 10 (to the -6) = .000175" as the maximum differential expansion. Using the Machinery's data would give a figure well under half of this, possibly approaching zero, or even being negative. You are welcome to calculate the stresses involved if you like, but the maximum stress will be at the smallest area to which the stress is applied, either the bottom of the hole or the threads. I always put a 1/4 ball bearing under the screw, so that the screw doesn't chew up the seat, in the event that the air pipes need to be replaced in future. Never lost threads or had the screw and ball get loose, so I reckon the stresses are below the yield point of the material. Putting a big wrench on the standard size bolt head (5/8)for a 7/16 bolt could be an issue I suppose, another good reason to use the allen or slotted screw and a reasonable feel. Another reason for the ball is that the holes are not threaded to bottom, since the OE fittings don't require it, and the screw will run out of thread before it bottoms, which IS a problem. Use anti-seize on the screw. If you really want to worry about it, you could make and thread plugs of gray cast iron, or make them of a 400 series stainless, most of which are near 5.5 to 6.5. Or you could mix your own alloys- 28% or 40% nickel in iron gives a coefficient of 6, 36% is near zero (invar), and less than 25% or more than 45 can kick it up past 10 - be precise. Other than these calculations, I think worrying about casting defects is like worrying about aircraft engines falling on your head, could happen but ain't gonna! Been fun! FRM |
| FR Millmore |
| I feel i've just been back in my metallurgy classes back in the 60's --after which I worked in non-ferrous fastner field. Thanks for the memories guys !! |
| Gil Price |
| FR- Not bad for an Attorney! The steel manifold studs and their threads in the head are engineered to work together, while a solid steel Allen-headed plug and the threads in the air injector ports are not, so your reasoning in that case is somewhat fallacious. I'm sure that you're aware that of every ten head castings that Peter Burgess examines for their potential for rebuilding purposes, he has to reject nine due to cracks having already developed, usually in the vicinity of the exhaust valve seats for #2 and #3 cylinders. In our case we aren't dealing with brand new gray iron head castings, but old, tired ones. Having your head reworked by an expert such as Peter is not cheap, but highly worthwhile. However, the prerequisite removal of material from the interior of the passages and combustion chamber further weakens the casting. Putting it at risk by using Allen-headed steel plugs when you could use something more appropriate is just plain foolish, no matter how minimal you think the theoretical risk may be. In our reality, it's usually worse than you might think at first guess. |
| Steve S. |
| FR- Oh, by the way- Jamming a ball bearing between the bottom of the plug and the seat would both concentrate and increase the thrusting stress on the thinnest part of the port wall. Ba-a-a-d practice. |
| Steve S. |
| And here's where I'll buck the crowd -- having driven my car both with and without the air pump (the DPO had "ripped all that crap off" to use the common phrase), I find that from the driver's seat I can tell absolutely no difference in performance, and the engine seems to run better with all the emissions gear in place & functioning correctly. And I happen to think clean air is a good thing, so it makes sense to me to make sure my MG is as clean as it can be -- to do otherwise is irresponsible. I say keep it on! HTH! |
| Rob Edwards |
| Jeff, If after reading the above responses you still want the allen set screws, Atlanta Imported has them in stock. John |
| John English |
| Just to weigh in, my head has the solid plugs seated deep into the air holes, and has since before I bought the car 9 years ago. That being said, I have a crack in the head just above the #3 cylinder that weeps coolant. - unfortunately this was noticed after the head was ported/polished/rebuilt 3 mos ago- the crack might have been there before, but now that its been removed and replaced, is now leaking. Never thought about the solid plugs in the air holes as leading to the crack, but it sounds plausible. Erick |
| Erick Vesterback |
| Thanks guys for all of the responses. I am sorry that involved so much effort on everyone's part. I'll do the easy thing and just see Lamar and Tom and grap 4 from Atlanta Imported. I agree that the air pump and all would be nice to have - but mine are missing. I am trying to replace some crude plugs that the previous owner had installed. I certainly learned a great deal about expansion and so forth - and appreciate those comments. Thanks so much. Jeff |
| Jeff Delk |
| Hmm - no comment on the bottom the bolt and crack your head idea, just an alternative. Take a UNF bolt and smear it with JB weld or some other epoxy sealer. Run it in (but do not tighten). If you don't mind the look of little hex heads, then you are done. If you want a cleaner look, wait until the sealant cures and zip the bolts off flush with the head using a high speed cutting wheel. Alternative - use the Allen head bolts but don't run them in all the way, just rely on the sealant. There you go - sealed and yet you'll be able to sleep at night not having to worry about having caused an impending crack. Of course you might still lie awake wondering about an impending crack from any of a dozen other areas and causes...... |
| Bill Spohn |
| >I agree that the air pump and all would be nice to have - but mine are missing. Mine were as well. I sourced all the missing components and reinstalled it all..... |
| Rob Edwards |
| Rob - were you able to have the pump rebuilt or was it in good condition? Any leads on where those items were located - was it just Ebay? Thanks, Jeff |
| Jeff Delk |
| I got all my stuff before eBay had taken off, but ebay is of course one place to look. I got the gulp valve through a wholesaler named WorldPac. The valve I got is actually a Nissan valve, but works just fine. The only difference was that it lacks the mounting ears so I just zip-tied it to the bracket. WP don't sell to the public, but they sell to just about all the European and Japanese independent garages and parts houses, so you should be able to find a local jobber than can order from them. The air rail and hoses I got from a vendor now out of business: Special Interest Car Parts (SICP). WorldPac probably has everything they had, though. I bought a good used pump from Scott Harper at Team Triumph in Ohio. Of course there are also all the usual suspects: Moss, VB, B-Hive, Little British Car Company, Roadster Factory, etc. For Moss stuff, I usually buy from Chris Roop at Roop's Automotive in Oregon or Tony Barnhill at The Autoist in Alabama. They both discount Moss retail prices. Engel Imports is another good place to check. I used to buy a lot of things from them when I was parts manager for a local British car garage.... HTH! |
| Rob Edwards |
| I bought tapered brass hex-head plugs at the local Lowes (HD didn't have them). The taper matched the holes that the air manifold originally fit in. I think they were in the hardware or plumbing isle with other brass fittings. I don't have the part number anymore, but I do know that they were about $0.65 each. |
| glq Greg |
| I wrote an article on the subject, but it's nowhere near as engineering specific as some of the above threads. http://www.flowspeed.com/air-plug.htm I've been using this technique for years and have never seen it fail. I've also seen many heads come in which have already had this done and also have not suffered because of it. I've also seen heads done with the ball bearings. I've seen nearly everything you can think of used to plug these holes, including the original injector "bolts" with ball bearings under them! In my experience thus, it's not the problem spot from which cracks originate. I'm not going to say anything more than that. Sean |
| Sean Brown |
| After waiting for the pot to boil a bit, I will note that: 1 I really don't know what to make of the attorney crack. 2 Engineers are guys who think about what should/could/might work. 3 Mechanics are guys who know what does work. They see what the engineers got wrong. 4 Technicians are guys who get paid to do mechanic's work, whether they do it well or no. They replace parts to make the engineer's error go away temporarily, without understanding. Amateurs do the same for free. 5 The benefits of having your head modified by experts are maybe clear, but as expressed have nothing to do with the discussion 6 Cracks in the seat are also have nothing to do etc. 7 Same for drastically modified ports 8 External seepage from pinholes or even cracks is not nice, but I know of several cars that have been operating with such for 10 or more years. The most astonishing being one that a customer owns nearly 20 years now, which has a crack from the pushrod holes straight across the head and down through #2 plug hole. Would I put a lot of work or even a regular valve job in such a head - hell no! 9 I would possibly consider a 90% failure rate if Peter or maybe Sean reported it to me, but not by hearsay. In doing several hundred heads over 40 years, I've only seen a few cracked, usually due to obvious overheating or continued use with burnt valves, though we never used to magnaflux them, since there was no big cracking problem. 10 Bill, DON"T let them have JB weld, or we'll be finding it squished down the ports! 11 Greg, The holes are NOT tapered, and the plugs you used don't have the correct thread. 12 Nobody has commented on my remark re the thread runout in the hole, and the stresses induced by screwing a bolt down in such threads, without taking measures such as my ball bearings. 13 Most astonishing, not a SINGLE person has been motivated to go LOOK AT a cylinder head. Doing so would indicate that the bottom of the threaded hole is about 5/8" from the port wall, and NOT on "the thinnest part" All stresses induced by the plug/ball will be within the quite substantial boss that extends from the head external surface to the port, at approximately the longitudinal center of the boss. The boss is blended into the head stud boss as well. I have never had the chance to cut into a head to see the exact disposition of metal there; perhaps Peter or Sean has. 14 While as indicated I quite enjoy arcane possibility discussions with informed and thoughtful adversaries, it is annoying to do so with no attention to points raised. Whence cometh the mystical "iron bolts"? Is it understood that my rough calculations of miniscule differential expansion are probably unobtainable maxima, well over any probable real movement? 15 And I feel it is irresponsible to foist these (#14) off as real world possibilities on unsuspecting folk who are simply asking for help in getting their car to work 16 Finally, as direct comparison to those unnamed, I will thank Jeff Delk for obviously having read and publicly appreciated the efforts of all answering. FRM |
| FR Millmore |
| I come late to this discussion but I have to support FRM & Sean - I have never seen so much misinformation! There is just no way a steel bolt inserted into the air injector drillings is going to crack a head - I don't care how well or badly it is fitted! My practice is the same a Sean's but I use a thread locking fluid and set the grub screw flush with the top of the casting, not tightened down. My experience with cracked heads and discussions with Peter B indicates that only around 1/3rd of heads are cracked. The ratio is higher in heads that are stored off the engine and lower on heads fitted to engines. |
| Chris at Octarine Services |
| Yo--Fletcher. My daughter just married an Engineer who is about to graduate from college and hopes to be able to support her. Thus, while you and I know about engineers, do not let the rest of the world know. Please. Theresa, who helped to restore to driving condition the 77B which she learned to drive on, and, which was present to drive her away from her wedding using wedding cars tonbridge (I drove her mother away from our wedding in my 79B, purchased, new, in Germany). Beyond these minor complaints, I am not competent to speak. We have emissions testing in both Maricopa County, where I live, and in Pima County, where Theresa and Kyle live. Thus, we are running full polution control gear on both cars. As to losses because of the air pump being connected, Theresa's car, with a Peter Burgess "Econo Tune" cylinder head will give my 68 GT a run for its money any day. Due to some interesting technicalities, Theresa's car does not have to have a cat on it. (Car was imported from Texas, many years ago, and the cat was not installed. The book used by the emissions people say from "75-80, MGB, some had a cat installed.) Her car, without a cat, is required to meet the same emission testing standards as a car with a cat installed. It has always done so. Not sure whether the air pump actually does promote burning of the "unburned fuel particles in the exhaust system" or, as I believe, simply dilutes the tail pipe emissions. But, as the current system is set up, the emissions are fine. As a somewhat, in my old age, "green person" I would like to know what is actually the best for the environment. Unfortunately, our various governmental organizations do not wish to discuss this. Thus, we do what needs to be done. However, I would note that the Peter Burgess cylinder head, on a .020" over bore block with a chrome bumper cam (regrind) meets emissions standards. So does the Mike Brown cylinder head on a 79 B, with .040 over bore and a chrome bumper cam (with a cat). Thus, the decision to remove the air pump and the air rail an idividual decision. A rebuilt engine, with a good cylinder head, is a very efficient engine, fully capable of meeting the emissions requirements for that year. An older, worn, engine might not be. The decision is a personal one. Les |
| Les Bengtson |
| Chris. You were posting while I was composing. Here in the US, about 80% of the cylinder head's for the late model rubber bumper cars, tend to be cracked when inspected. The earlier cars show a much lower tendency to crack. Do not know why this is unless it is due to the rear water take off port that was used with the Z-S carb. When I wanted to purchase a cylinder head to have modified by Peter Burgess, for my daughter's car, we rejected several cylinder heads that we could see cracks in, then, took the best we could find down to the local machine shop to have "Magna-Fluxed". One, of the four that had checked good vistually, passed the "Magna-Flux" test. That one was sent off to Peter Burgess for modification to the "Econo-Tune" specification. (Highly recommended by a member of the MGA board and very highly recommended by me.) The people who provided this service, Bob and Gil Schaulin, have been friends and supliers for a number of years. My experience, and Bob and Gil's have been with cylinder head that were on the engine when removed. About 80% of the RB cylinder heads have shown cracks when inspected. About 50% of the CB cylinder heads, Gil informs me, show cracks when inspected. This ratio may be different in the UK due to design differences. But, my own investigations, and those of whom I respect, indicate that the US cars (North American Specification) have a very significant problem with cylinder head cracking. Les |
| Les Bengtson |
| Thanks Chris & Les. Some believable if depressing data. The cracked heads I've seen were all late model, 18V. One weeper (Visibly Flawed casting) was a 1500 head (on a 79B!). I would like to know where these cracks are: critical areas like chamber and ports or external? It is possible that there were pattern changes to reduce weight and cost that result in these cracks. It may also be a result of too many moronic installation and maintenance procedures relating to head gaskets, torquing of bolts etc over the intervening years. I have learned from this board that popular myth likes to attribute evil consequences to parts that have been sitting unused; I think this as myth is either a result of the socio-religious proscription of indolence (!), or perhaps more likely has an actual basis in "parts off the engine were probably taken off for a reason". Which holds even if nobody actually figured out WHY the removed parts or those they were attached to didn't work right. Interesting (and convenient for some) about the cat requirement - 75 did not have cat, 76-on did; much more interesting that Teresa's car meets cat specs without one. The AI system does burn (some of) the unburned hydrocarbons - that's why there are nozzles in the ports under discussion. They direct air to the hottest area of the exhaust port, just behind the valve, so that the exhaust WILL burn. Figures I've read indicate that the AI pump uses about 2 hp, tolerable if the system and the car are otherwise OK. The trouble is, and was when the cars were new, the system and parts thereof were unreliable. This leads to poor running and worse "repair", giving bad air. I leave correctly functioning systems alone, screwed up cars with missing pieces get sorted out and made to run correctly without the AI. There is also an issue with NOx levels rising as HC levels fall, which may mean the AI issue is a wash on non 3-way cat cars. Finally, I have nothing against engineers per se; I have a considerable issue with the implied or stated idea that BECAUSE a doofus has a degree, his opinions are necessarily better than those of a Mechanic without one. I had this arguement with my professors at Carnegie Tech, now Carnegie-Mellon, and departed said school partly as a result of my youthful frustration that they could not see that the basis of science AND mechanics is observation, which ALWAYS MUST override theory. It is good to recall Richard Feynmann's press conference, in which he demonstrated that the engineer's shuttle engine seals were not good, by doing what any real Mechanic would do - Let's SEE, get it cold and try it. I have always maintained that nobody should get an engineering degree, or be allowed to design anything for production, without substantial and ongoing field experience. "Let's take a look" is the mantra of the Mechanic. FRM |
| FR Millmore |
| FRM, In my experience I have only seen one head that had cracks from the valve seat out across the camber roof. The common places for cracks (and early heads are no different than late ones) is from just above number 2 & 3 plugs, diagonally towards the centre stud hole, often crossing the rocker cover gasket flange an inch or so away from the stud hole. Also the flat area between the valve guides by the centre stud hole. The casting in these regions is only 1/8 inch thick at best and is just mechanically weak! |
| Chris at Octarine Services |
| Thanks, Chris. All the cracks I've seen were vertical up the side above #2 or #3, not impinging on the stud bosses, on non-cooked heads. FRM |
| FR Millmore |
| How you block off the air injection ports is about the most mundane obscure issue known to mankind. The response and opinions have been in an inverse relationship to the importance of the issue. I think this thread needs to be specially flagged and and maintained for posterity, for those who follow us, to analyze and ponder. All I know is those air pumps that lasted a little longer than you got the car out of the dealer's lot are now being sold by hucksters on ebay as superchargers. Maybe they could be used in some way to bring down an airplane when stowed in baggage. Barry |
| Barry Parkinson |
| Barry- Your first sentence is possibly true, as implied in my first response to SS, except that the real issue of the discussion is not the blocking of the ports. The issue is, in the instance of the bolt sellers, being competent to do your job; and is, subsequently to SS' 1st post, what is a responsible and reasonable response to an apparently simple mechanical problem, and how such 'simple' things do go wrong. All with additional input to both answer the original question, and wrest some real data from the exchange. With that difference in defining the "issue", I would suggest that most of the response is STILL lacking in observation and analysis. Your second paragraph is perfect. A good teacher could easily make a semester's course out of the discussion, and a good student could gain a life's wisdom from it, without a teacher. I have done the second, and would gladly conduct the first as seminar, with the payment of suitable fees! Para 3 is a sad commentary on those who pay no attention and hence know not what they do, and possibly on the malicious use of a slight facility with words; we are not informed as to whether the hucksters are only avaricious and scheming, or are also uninformed and deluded by simplistic reasoning. As to para 4, please don't suggest this to those on either side of the security line! FRM |
| FR Millmore |
| FRM Thanks for your thoughtful analysis, it provides me with additional insight into these smoggy issues. Barry |
| Barry Parkinson |
| Goodness - I feel as if I have opened Pandora's Box on this one. Just another word of thanks for all the detailed information. I was away from the puter for a few days and was shocked to see all of the responses. Thanks again guys! Jeff |
| J Delk |
| I vote for the 7/16"-20 UNF fine-threaded iron bolts 3/4" in length. I put those in my 69 MGB two years ago and have had nary a problem. I also used a dab of Permatex on each to insure a good seal. |
| Tom Fisher |
| Tom Perhaps I missed something, (I got confused as the conversation bounced back and forth - an I am not about to read the whole thing again) but 1/ how do you know the bolts are iron (as contrasted with steel) and 2/ where do you get iron bolts? Barry |
| Barry Parkinson |
| Barry Asked: "How do you know the bolts are iron?" Hi Barry: That was an oversight on my part - I'm sorry. I really don't know. I just went to Ace Hardware and said I wanted the 7/16"-20 UNF fine-threaded bolts 3/4" in length. I took what they gave me. They have a silvery look about them - probably steel. They work fine. |
| Tom Fisher |
| Tom You blew it! Steel has a mu difference in expansion rate from iron. You must replace all manifold studs, rocker arm bolts, and thermostat cover studs with iron. It is especially advisable to change the bolts on the heater control valve as that area is subject to substantial temperature changes as the water exits the engine to be cooled in the cabin heat exchange process. The spark plugs are an area of great concern as they tend to heat & cool on an irregular basis as the throttle is opened and closed. Your advice on where I can get iron spark plugs will be appreciated. On further reflection I realized the valve seats may have been inadvertently modified from the original iron to steel. This is an issue that needs to be studied and addressed. Valve guides likewise are no longer iron. Finally, (so far) I note that pistons are made from an alloy that greatly expands and contracts. Apparently only for cost purposes, manufacturers have generally changed to alloy pistons from iron or steel. There may be appropriate aftermarket pistons available. Barry |
| Barry Parkinson |
| Barry said: "You blew it! Steel has a mu difference in expansion rate from iron. You must replace all manifold studs, rocker arm bolts, and thermostat cover studs with iron. It is especially advisable to change the bolts on the heater control valve as that area is subject to substantial temperature changes as the water exits the engine to be cooled in the cabin heat exchange process." Huh? I think I'm sorry I said anything. Oh, BTW, I'm not changing anything. My engine purrs like a kitten - and has for quite some time. |
| Tom Fisher |
| Geez, and all this time (about 18+ yrs now) my poor ol' 18GF has suffered with ARP head studs and the suggested (for years taken as gospel) Allen screw air rail hole plugs. I will not say that this is the best practice, but it is an empirical experience. Not being an engineer, or metalurgist, it is entirely possible that these things are all wrong. I will say, however, having had the head and deck surfaced and cast iron valve seats installed about 10 yrs ago, no one found any cracks when magnafuxed, and the poor old beast runs the best it ever has. It does make me wonder just HOW important this whole question is in practical application, and if actual operating parameters aren't a bigger factor in whether the limits will ever get pushed than the absolutes of engineering and metalugy. Perhaps the engineering from BMC/BLMC designed in a wide margin of safety just for reliability's sake. I look at this question having had experiences where the supposed best possible combinations of the various elements for some similarly stressed assemblies accomplished nothing descernible, or actually made things worse. In the end I guess all I can say with any certainty is, "so far, so good" and "follow your best research." An interesting thread. |
| Bob Muenchausen |
| Bob M. said: [It does make me wonder just HOW important this whole question is in practical application, and if actual operating parameters aren't a bigger factor in whether the limits will ever get pushed than the absolutes of engineering and metalugy. Perhaps the engineering from BMC/BLMC designed in a wide margin of safety just for reliability's sake. I look at this question having had experiences where the supposed best possible combinations of the various elements for some similarly stressed assemblies accomplished nothing descernible, or actually made things worse. In the end I guess all I can say with any certainty is, "so far, so good" and "follow your best research." An interesting thread.] You said it, Bob! And I wholeheartedly agree. It all reminds me of how, back in the 50s, all the mechanical engineers said that, due to the limitations of the coefficients of friction, it would be physically impossible to ever exceed 150 mph from a standing start in the quarter mile drags. Guess some of those California hot rodders didn't read those same books. God, that tickles me! |
| Tom Fisher |
| As my father said when I was embarking on an engineering co-op program (sandwich course in the UK) - "if it doesn't look right it probably isn't". That, and "measure twice cut once" served me well in 40+ years of my engineering career in the power equipment field. BarryQ |
| B.J. Quartermaine |
| When I put an exchange engine in my car in about 1972 it came with a federal head. It had a set of bolts blocking the air injenction ports. That worked fine until 1995 when it went away to be bought up the Peter Burgess big valve spec and when it came back it had a neat set of flush grub screws fitted there. Other than thinking how much tidier this looks every time I change the plugs ( about every other year with the mileage our car covers) that's all I know! I think from this we can conclude that done sensibly this is a non problem, oh and on emissions, although my car is of an age when "no visible smoke" is the requirement I have had it checked at MoT time out of interest and it would pass today. |
| Stan Best |
| "It all reminds me of how, back in the 50s, all the mechanical engineers said that, due to the limitations of the coefficients of friction, it would be physically impossible to ever exceed 150 mph from a standing start in the quarter mile drags. Guess some of those California hot rodders didn't read those same books." Why California hot rodders? Art Arfons, from Ohio, is credited with being the 1st to break 150mph in the 1/4 mile. He used an Allison aircraft engine. He built all the Green Monsters, piston engine & jet engine versions. The "King of the Dragsters" is of course Big Daddy Don Garlits from Florida. He was the 1st to break 170, 180, 200, 240, 250, 260, and 270 MPH - First to top 200 in the 1/8 mile. |
| Carl Floyd |
| Carl Floyd wrote: "Why California hot rodders? Art Arfons, from Ohio, is credited with being the 1st to break 150mph in the 1/4 mile. He used an Allison aircraft engine. He built all the Green Monsters, piston engine & jet engine versions." You're right, Carl - I knew I'd get in trouble for the California comment. I saw Art Arfons & his Green Monster run many a time. His ET in the quarter mile was nothing to write home about (poor acceleration) - but the top speed was something else. Ha, I remember once when he got the thing sideways about 2/3 of the way down the strip. You talk about some people scrambling to get out of the way! ;-) |
| Tom Fisher |
| I just now came back to this thread and read all of it. Wow, what have I done! A tempest in a tea cup! FR- The remark of "Not bad for an Attorney" was not intended to be a crack. I had you confused with someone else who used to be a regular poster, and it was intended to be an "inside joke" between the two of us. I would've expected him to respond along the lines of something like "Not bad for a retired cop!" The nine out of ten" statistic came from Peter Burgess in an Email, so you'll just have to take my word for it. Perhaps he was speaking figuratively, or perhaps literally, I can't say. As for the availability of iron bolts, while rare in hardware stores, any shop that supplies boiler repair firms should have them readily available because they're a common size (7/16"-20 X 3/4"). Since you're in one of the "Rust Belt" states, they shouldn't be that difficult to obtain. If you're in a rural area, try Pittsburgh or Philadelphia (where are you anyway? Virginia isn't that far, you know). In my experience, I've seen a grand total of two heads that had cracking on the inside of the exhaust ports that extended to the air injector holes. Both of these heads had steel allen-head set screws installed in the air injector ports, hence my recommendation of using iron bolts instead. It certainly was not my intention to panic people into yanking out their set screws and replacing them with iron bolts, but rather to cause thinking people to consider a better alternative just in case they might have a head with a casting defect. I'll end with a quote: "such casting defects are not the norm, but, you never can be too careful........" |
| Steve S. |
| Fletcher, Like Steve S, I have been forced to work for a living and do not have as much time to spend here as I was when "self employed". Or, in Steve's case, working as a rather special form of Police Officer. (Steve--computer went down. Wife working on getting it fully up, but your previous e-mail is not, currently, available. Hope to have the full system up soon and will answer then. If you have not heard from me in a week, please e-mail me throught the website and I will answer ASAP.) Back to the main question. On my website, there is a tech article called, something to the effect, "Crack Inspection for the Hobbyist". This is one of my later tech articles and, due to my wife and daughters, contains photographs. (Bear to have married late, to someone much more intelligent than I am and having a wife and daughters who think digital photo are "easy" to make and put up.) Not for old men. The vast majority of the cracks I have seen have been in the area of the number three cylinder and have evidenced themselves by a line of coolant being visible. This is true on both the chrome bumper cars (semi-rare) and the rubber bumper cars (often). When the cylinder head is removed and a dye-penetrant test (as per the tech article) or a Magna-Flux (at the local machine shop we use) show, the external cracks also show up in the number three combustion chamber. I would accept Chris's argument that this is a basic design flaw of the system. I would, however, point out that the coolant flow of the later model, North American Specification, cylinder heads seems to enhance the probability of cracks being present. The later model cars have a water choke take off from the rear of the cylinder head that the earlier models did not have. Whether this altered flow characteristic has anything to do with the fact that the later model cylinder heads have a greater frequency of cracking (having tested a number of each), I do not know. Many years ago, I wrote a tech article on making a blanking plate to fit onto the rear of the RB cylinder heads. Paul Hunt, on his "Page of Bee and Vee" was kind enought to host the article and Moss seems to have had such a blanking plate as I described produced for sale. On the other hand, we have run the factory set up, using the rear water choke take off to supply heated water to the intake manifold for our Weber DGV conversions, for a number of years without noted problems. Do not know if this is due to my having torqued the cylinder heads down properly or not. I found that they needed to be torqued down after the initial run in of the rebuilt engine, then, at 250, 500 and 1,000 miles. After that point, the system held the proper torque and is checked, using a "clicking" torque wrench, set a 50 Lbft, annually. The last MGB was sent to the US over 25 years ago. I have a great deal of difficulty, today, deciding what was a design deficiency and what might have been the result of poor maintenance over the years. I have not, in my own experience, noted any problem with cracks developing due to the manner in which the holes for the air rails were sealed. I have seen both the allen set screws and bolts used with success. But, in an area where emissions testing is still required, the majority of the cars still have the air rails and air pumps attached--at least for testing purposes. My "rebuilt" air pump, from Auto Zone, and rebuilt by Cardone, developed a rough spot after three months of use and caused the entire engine to vibrate. Thus, I will replace the pump before the next emissions inspection. Current rebuilds are guaranteed for one year. My original rebuild was guaranteed for "Life". My original 79B had an air pump which lasted for 5.5 years, the time that I owned it. A new air pump, from Moss, seems to be holding up quite well on my daughter's car. Given a choice, I would remove both the air rail and the pump. I have seen no positive evidence that either makes for a cleaner running engine. A properly rebuilt, regularly maintained engine will have lower emissions than one that is in poor condition and not maintained. In all cases, the condition of the engine, and the attitude of the owner, make a most significant difference. Les |
| Les Bengtson |
| >I have seen no positive evidence that either makes for a cleaner running engine. Les, with all due respect, have you seen any positive evidence that having the emissions gear in place & functioning properly *doesn't* make for a cleaner-running engine? I'd find it hard to believe that the factory would go to the expense of installing unnecessary parts. Jeff, I saw a post on another forum that indicated a Gates hose (part number 18749) works for the pump-to-gulp valve hose. It just needs to be trimmed to fit. I have not confirmed this myself, but it's worth checking out if you need one. HTH! |
| Rob Edwards |
| Rob. With similar respect, I have never seen any real testing done to show what effect the various "emissions control systems" have on the overall operation of the engine. By this, I mean someone who is a trained researcher taking several cars and testing them, using a chassis dynamometer (rolling road) and a five gas analyzer to determine which parts of the system really accomplish anything. From my own experience, I can tell you that my 68 GT, which was purchased without the air pump and rail installed, passes the local emissions test without it. My daughter's 77B, purchased without a cat installed, passes the emissions test without it. There is some discussion about what an air pump actually does. One group feels that it helps the burnt exhaust gasses continue to burn while they travel through the exhaust system producing a cleaner byproduct at the tail pipe. The other group feels that all that is being done is to dilute the byproduct with air, thus lowering the registered emissions at the tail pipe. The latter interpretation makes more sense to me for a couple of reasons. First, if we are to take "burnt" gasses the, by definition, are already past the stage of being able to burn again, especially without the addition of some form of ignition mechanism. Second, the basic exhaust system was not re-engineered when the various polution control systems were added on, piecemeal, to the engine. Such a re-engineering would, in my opinion, be necessary if the purpose of the system was to contain burning gasses, rather than to allow already burned gasses to pass through it. With the addition of the cat, the system was re-engineered and proof of its effectiveness can be seen by using an infa-red thermometer to measure the temperature of the exhaust gasses going into the cat and exiting the cat. The 100+ deg F increase in exhaust system temperature does indicate that the cat is functioning to allow unburned fuel to be consumed. Most of these cars are driven on a "pleasure basis", seldom on a daily basis. Thus, I doubt that any pollution they might put out would be statistically significant in light of the other sources of pollution in their area. The best concept is a ground up engineering effort to produce a cleaner running engine and that form of transport becoming the majority of the automotive population. This is what we have seen over the years and the end result is far superior to the add on measures of the late 60's and 70's. Thus, I do not get upset if someone wants to make a personal decision to "de-tox" their cars. Les |
| Les Bengtson |
| J Delk, You can find the plugs on eBay. Pete |
| Pete W. |
| This may not be relevant but it has been said that the most common cracks are between the number 2 and 3 spark plug holes and the stud hole that is between them. That stud hole is the tight one. It is tight so as to enhance head location. Could it be that its tightness encourages head cracking? Given Fletchers tutorial on expansion rates I guess this is unlikely. However, rust in that stud hole does cause it to stick making removal a problem. Is rough removal causing addisional stress and encouraging cracks? |
| David Witham |
| Well guys - we have the distinction of hitting the 50 mark on responses. I have the allen head plugs and will let you all know if I have any problems. The head was magna-fluxed prior to having new seats installed and I'll be mindful of all the points raised. Thanks again for the great info |
| J Delk |
| Rob- Consider the fact that the hot exhaust gases pass through the exhaust system in pulses, not as a steady flow. When a high-pressure pulse of exhaust gases is passing the air injector port in an exhaust port, an anti-back-flow valve prevents the hot gases from entering the air injector system to any meaningful degree. The air injected into the exhaust port can enter only when pressure has dropped, which is after the inertia of the exhaust gases has carried them past the air injector port, leaving a low pressure area in their wake that allows the anti-back-flow valve to open. This being the case, the air that is injected is always sandwiched between the pulses of exhaust gases, mixing with it only after entering the turbulence inside the muffler, at which point temperatures have dropped to the point that combustion has ceased, thus accomplishing little other than the dilution of the exhaust gases exiting the exhaust pipe. Way back when the system was introduced, the EPA measured for pollution in only terms of a standard of "parts per million" (PPM, as they called it back then), thus the diluting system helped to satisfy the EPA standards, along with such tricks as leaning out the fuel/air ratio and changing the ignition timing curve to initiate combustion earlier during the compression cycle. However, several ecologically minded scientists and liberal politicians, emboldened by having succeeded in forcing a ban on leaded fuels, loudly protested that the technology being used by the shameful capitalist auto industry was a sham perpetrated at the expense of the poor suffering masses in order to prevent them from spending millions of dollars of their precious plutocratic profits on the development and use of "meaningful" technology. This hue and cry was quickly taken up by a coalition of university faculty and students named Students Wildly Indignant about Nearly Everything (S.W.I.N.E. for short) which picketed not the EPA building in Washington, D.C., but the Supreme Court building (the officially appointed all-purpose protest site for the Politically Myopic). When the EPA responded to the political pressure by changing its test standards to reflect actual total pollution emitted, manufacturers quickly dropped the air pumps and switched to catalytic converters. I lived through this era of tumult as a young adult and remember it all too well. May it R.I.P. (Who said that this BBS is dull?) |
| Steve S. |
| I don't recall it being as conspiratorial as Steve described. It was known more than 4 years in advance that emissions standards would be tightened for '75 vintage autos, and that the only practical way to meet those standards was with the catalytic converter. The huge issue was precisely controlling the unburnt fuel being sent to the catalytic converter to allow it to get hot enough and burn the fuel residue. Two or 3 part converters actually inject air to increase the oxidation process. Ironically you need waste fuel to keep the converter hot enough to function. As, I recall, Mitsubishi was the only mfg who sold a car in the US in 75 that met epa standards that did not have a cat. It ran like crud and required frequent adjustments/tune ups to keep the emissions legal. The cars with cat's didn't run much better. I recall 1976 Mustangs being the hi performance car with 0-60 times of over 10 seconds. The big change cam with precise fuel control with multipoint injection. The epa does not check pollution above 65 mph. The manufacturers typically go to a more efficient computer setting above about 65 mph. Many newer cars get better mileage at 75 than 65 because of the factory computer tuning. |
| Barry Parkinson |
| Steve. Very well said. Wish I had that degree of knowledge available. But, I appreciate your informing me, and Rob, of the technical aspects of what I only suspected. My computer crashed a few weeks ago and I did not have the opportunity to respond to your off line e-mail. We have the new system up and running, but the old, saved, e-mails are not yet up, and may never be. Please shoot me a "test" message to put your e-mail address back in the address book and I will ask you my question about poly bushings for a rubber bumper car. Thanks. Les |
| Les Bengtson |
| Steve, Loved that! You have made my day. I had feared such poetic expression was a lost art. Regards Roger |
| Roger T |
| Steve, Les, I appreciate you comments, but cannot fully agree. Les, you say that "One group feels that it helps the burnt exhaust gasses continue to burn...." I agree with your assessment that burnt gasses cannot continue to burn. The intent of the air injection system however is to allow UNburnt gases (i.e. unburnt HCs -- fuel) to burn by providing oxygen for combustion. Steve, you say that "the air that is injected is always sandwiched between the pulses of exhaust gases, mixing with it only after entering the turbulence inside the muffler..." There is a lot of exhaust plumbing between the head and the muffler. I would expect there to be mixing of the exhaust pulses and injected air pulses long before both reached the muffler. The exhaust pulses will be entering the port much more forcefully than the injected air pulses -- this in itself should create some mixing. Gentlemen, I respect the knowledge of both of you and acknowledge that greatly exceeds mine, but I don't think the matter is as cut and dried as it seems. I have no numbers and cannot cite a primary source, but I have seen it said that the reduction in emissions from the air injection system exceeds what would be expected from simple dilution. If this is the case, then there must be some addition combustion occurring outside the cylinder. I would be very interested in finding hard evidence of this. Until then, I will continue to err on what I believe to be the side of caution and continue to run all the emissions gear that the factory installed. It helps me sleep better at night. ;-) Many people make the argument that "I only drive the car a little bit, so I'm not making that much pollution. I find that argument fallacious -- no different from "It's ok if I pee in your coffee just a tiny bit." Cheers! |
| Rob Edwards |
| If I use the bolts instead of the allen screws, should I then change over to synthetic oil? |
| Jason |
| Rob. We can argue this point forever. Unless someone decides to do a test series to determine what actually works, all we can offer up is opinion, not facts. Such items as "unburned hydrocarbons" is a perfect example. We know they exist because they can be measured. We do not know if, by injecting fresh air into the exhaust gasses, they will be at a mixture which would be capable of burning even if there were some form of triggering device to cause them to re-ignite in the exhaust system. Fuel/air has to be mixed in the proper ratio to be capable of burning and the tolerance on either side of the chemically correct mixture is rather small. Until I can see some properly performed tests which indicate that the addition of outside air to the exhaust gasses causes them to re-ignite and burn completely, I will remain a sceptic. In the mean time, a well tuned and maintained engine is the best method of polution control and I need to get back to tuning mine. Les |
| Les Bengtson |
| Jason, Atlanta: NO, but you should check your blinker fluid regularly and grease your exhaust bearings every 500 miles after the change. I'm dead serious... Sean |
| Sean Brown |
| Sean - do you get your muffler bearings (and the trick cross drilled brake lines) from Kale Auto? BTW - Barry, I didn't know Mitsubishi managed to meet '75 emissions w/o a catalyst. Frankly we were pretty lucky GM Research stumbled upon the catalytic converter as the regulations were formulated without the technology available to meet them! In any case, the very fuel inefficient thermal reactor was an early technology as well, BMW and Mazda tried it. The other, more successful attempt was Honda's application of diesel-style prechambers to create a workable stratified charge in their CVCC engines. These worked quite well, until tightening regulations made Honda revert to by-then conventional catalysts. |
| John Z |
| The new Toyota Corolla I bought in 1976 didn't have a converter. In 1979 I bought a new Civic and an Accord because they didn't have converters and could use leaded fuel. Clifton |
| Clifton Gordon |
| As I recall, the Calif regs were tougher and there were several vehicles in the mid '70's that passed the Fed regs w/o a catalytic convertor, but not Calif regs. Barry A current rant: The new mtb free gasoline makes a big difference in gas mileage, at least with modern cars. My 2001 Olds has jumped from a typical road trip mpg of 27-28 to 30+ The e85 stuff though is supposed to get much poorer mileage. How much difference the mtb free gas makes in a carbureted carb though may less significant. |
| Barry Parkinson |
| Gentleman (and Ladies). This is a great threat and one of the logest for some time. I owned a 68 B back in 1980. It was a real bother to get it to pass smog in California back then. I purchased it without the equipment attached and had to attache it to pass. I had a friend who owned a smog shop and had him run the car prior to putting everything back on. It passed. With all the stuff on, it did not pass, but I am unsure the air pump was working correctly. At that time, the regulations for passing were not as strict. I remember my friend running the car and slowly accelerating it until the monitoring maching showed it was in compliance. At that point, he hit the printer and gave me the resutls. We sold the car shortly after. My solution? I bought a 67 B GT without smog systems. |
| Bruce Cunha |
This thread was discussed between 04/08/2006 and 19/08/2006
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