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MG Midget and Sprite Technical - straping center main bearing

does anyone have any thoughts on this mod for this three main bearing crank? Crank flex and all that.I'm talking a reasonably stock road car here. Bob C
chamberlain Bob

When I took my crankshaft to be balanced and reground, the engineer first thougt it was bent by the look of the wearing pattern on the journals.
Once it was in the lathe and measured it turned out not to be bent but worn uneven due to flexing in the middle.

So, yes, it is worth it, even on mildly tuned engines.

(I did rev the "old" engine sometimes....)
Alex G Matla

Hi Bob

We only strap our Race and Track Day engines.

Peter
P Burgess

I've strapped mine, but then it isn't going to have an easy life of it.
Brad 1380

is it in my opinion always good to over build your botom end.
gives that bit of insurance for when you shift wrong upgrade or what ever.

straped my center mains
did also have it linebored afterwards helps with sealing the rear scroll seal to
Onno Könemann

the only 2 down sides are

1. it will cost you an extra $75 for the kit and the machine work

2. there is a remote low odds possiability that the main cap can crack over time...but its a long shot.


That said I did mine, WHEN I asked my machine shop about it, they said they would highly recommend it, because its a 3 main instead of a 5 main, and the block metal is fairly thin even tho mine has a thicker base and ribbed,,,

It maybe over kill, and you will probably be okay without it, but if your there and considering the price of parts, Its hard not to do the mod, its just great insurance.

Make sure you get the correct one... the adverts are vary confussing make sure you get the A-series and NOT te A+ seriers

Prop

Hi Prop

We make all our own straps to suit. It is interesting that MGB 3 bearing owners do not rush to strap the centre main. I feel this is because of the 'Race/Rally' pedigree of the A series engines. EG people think they must have big 'early' Cooper S ex valves even though the factory later fitted smaller ex valves for reliability. The same can be said for 11 stud head conversions. The originals were only a little more than finger tight yet everyone fits 'proper' head studs and risks over crushing the head gasket. Another oddity is the insistance of some race drivers/engine builders using non-projected spark plugs which can reduce bhp. This, I think, is because some heads are milled/skimmed to such an extent that projected plug electrodes would be smitten mightily by the piston crown and the non- projected plugs are safe. Some people make very small shims to ensure the projected plug electrode is 180 degrees to the bore.

I do know that the midget engine is far stronger than the A+ engine and I try to steer folk away from the A+ heads and engines whenever I can.
P Burgess

Peter
All folk i know that wan a faster B-series engine take a 5 bearing one to start with.
So it may just be the case that they have the choice and there fore it is no issue.
On top of that the A is usualy reved a bit more than the B

Do like the free reving feel of a 3 bearing pull handle B
Onno Könemann

Hi Onno

I have pasted this from Keith Calver

Peter

Engine – Main cap issues 02.10.08 updated 20-12-08



I have been talking to more and more people recently about main caps, main straps and steel main caps and 4-bolt steel main caps. Most are somewhat surprised that I do not advocate using anything other than the standard caps. And that steel caps should really only be used where the standard one has broken or been lost (not a problem I have encountered!) - in other words as a rescue fitment rather than a planned replacement. Various reasons for this, but mostly because, contrary to popular opinion, main caps do not break – they are broken. Broken by errant drivers who continually carry out savage down-shifts – use the brakes to slow the car they are FAR more efficient at it. Or who continually over-rev the motor through missed gears. And broken through badly balanced rotating assemblies. Not a problem at road speeds, but in race engines they can be very destructive.

To be properly effective, a centre main strap needs to be ground flush as does the main cap face once machined off with great accuracy. For those that have cared to look at a main cap/strap when disassembled after some period of running – you will see where the main cap has rubbed an elongated, shaded in figure of 8 between the main cap bolts. Obviously the strap is not holding the main cap down any tighter/straighter. And really the main bearing housing should be line-honed after the strap is fitted as it slightly distorts the cap in a different way than when using no strap. Not the cheap fix/protection many believe. And just because some say 'I've always fitted main straps just as they are and not had any problems'. The question then is – have you tried running without them?

And steel main caps – whether 2 or 4 bolt types, need to be of a decently quality steel. I have had extensive discussions with friends and colleagues engaged in the performance automotive world as engineers and engine designers. They all have the same thing to say about the 4-bolt main cap. Without spending a fortune on proof testing the installation, so from a purely engineering point of view and considering the block to which it is being fitted, it is likely to weaken the block rather than increase the strength/support of the centre main. Yes, I know some of the A-series renowned specialists almost insist on their fitment – that does not make it correct. I suspect they are fitting them more to try and fend off the results of idiot drivers doing what I described earlier. Those that have taken the time to look will also notice that the bolt heads settle in a lot more in to a steel cap with no washer than they do in to the standard cast caps. This is because the standard material is much tougher/harder. A sobering thought eh?

Whatever you decide to go with, one thing I will say is a must – the use of proper, hardened steel washers under the main cap retaining bolt heads. I believe that most of the main cap movement in the performance A-series comes from the main cap bolt head settling in to the cap material in use. This allows the cap to move around, stress the cap material and cause the cap to shuffle and settle in to the block face, effectively releasing/easing the torque setting of the bolt - or stud if using them. The result will be a misshapen bearing housing causing oil pressure loss and ultimately cap failure. The centre main suffering most as it tries to contain the whipping mass of two piston and rod assemblies. ARP do some standard engineering type washers that I am using – part number 200-8530. It is likely you will need to grind a small flat on the edges of a pair of the washers – usually for the front main cap – to clear the crank web, check this with the crank and thrust washers in place. Where used in a Mini transverse (i.e. Mini) application you may well need to relieve the gearbox casing under the rear main cap bolt head positions.
P Burgess

Hi
Most crankshaft fatigue problems start with either out of balance bits at the rear, like clutches or even flywheels OR more likely loose or damaged harmonic balancers. That's my story anyway - Willy
WilliamRevit

Hi Willy

I haven't seen any 'dead' A series engines to have to work out what went wrong, most we see scrapped are 1380s worn out with nowhere to go but recycling. With B series I have seen three wrecked cranks, one broke the rear main cap. The other block survived two flat plane forged B cranks snapping. The loading on the bearings was plain to see. The cause in both cases ring gear moving on over mosified flywheels...I have learnt to always fit one of our own modded flywheels when we build/rebuild a race B!

I guess I am trying to say I agree with what you say so succinctly.

Peter
P Burgess

Peter
I know most of KC's article's as this one
that is why i have had it all machined to each other an line bored it.

As said in an other thread
for mere mortals like me it is very hard to judge which "expert" is right.
So i read most relevant books and articles and look at my or friends experiances and make my own judgement from there.

In this case most experts say it is usefull I do not know of failed cranks with straps and do know of failed cranks without straps.
So i reasoned that it must do some good if machined correctly.

making sure that the other parts (flywheel, damper) are good is of course all part of a proper build.

Onno Könemann

Hi Onno

I was only answering Bob with my own thoughts and experience when he asked whether to strap a fairly stock road engine. Once I am happy the saddle and caps are in good condition in terms of ovality and trueness one to the others I am as confident as I can be the centre cap will be ok unstrapped. Once we are enisaging 6500 rpm plus we tend to err on the side of caution and strap the centre cap. Line boring the main bearings entails lowering the cap a little by machining the bearing cap to block faces then line boring from front to back to resize the bearings, this does, however it is done, make the holes a little oval in the block. The alternative would be to machine the block and cap then raise the centreline of the crank towards the block face. I think I would reject a build on an A series engine if it needed line boring in the first instance, it might well imply a lot of other problems lurking in the engine. When A series blocks become really rare that may become a different matter!

Peter
P Burgess

mine sees the other side of 6500rpm sometimes (track days)
though on the road it is never needed to go above 5500 (always plenty power to anoy BMW's)
Onno Könemann

Thats some good points Peter and a great read by KC, Who Im such a fan of.


But you make a vary intresting comment... your saying you are finding the strap is moving in a figure 8 motion and the only time you strap an engine is for race purposes...

MMmmm, To me that reinforces the need for a strap, becuse what is causing all that figure 8 wear,, Im guessing the block is flexing, would that be correct? If that is true, then how much flex would be happening without the strap

You will have to forgive Onno and I, as we are like alot of other amuture engine builders, We read, we listen, we spend time thinking about the info and then we roll the dice and decide what mods to do based on the avialble facts. In the end I think we are better builders then our for runners of even 10 years ago in the ameture build world due to the avialibility of lots of info from the likes of vizard, stapleton, and culver. But we also are subject to making alot of bad choices like 13:1 CR heads, 11 stud conversions, and knife blading the butterflys, we just dont have the luxury of knowing whats good and whats BS

perhaps someday someone will write a book telling what MODS NOT to do, Now that could be an end of the world read...LOL.

Prop
Prop

Hi Prop

I think Keith means in hard use the cap has a tendency to walkabout even when strapped. As you say maybe some sort of flexing/lozenging of block. It shows the need to inspect/rebuild highly stressed motors on a regular basis...regular meaning before problems occur (obviously differeny schedule for different engines and specs).

I have known Keith for around 20 years, he has a wealth of information/knowledge and sound advice. He is always a most welcome visitor when he draws up outside our unit on his motorcycle.

Peter
P Burgess

Onno
Theory #
Maybee the engines with strapped maincaps last longer because the owner going to the extra trouble of this sort of work is the sort of person that is going to have better quality parts in their engine anyway and go to the trouble of checking/balancing and assembling with greater care - Their engine is probably going to last longer, regardless of it being strapped or not.
Willy
WilliamRevit



Peter,

Whew, You had me worried after reading the KC artical...I was thinking Oh great! Now I got to pull the center strap off my engine or the bearing will freak out because its elongated out of round and will blow up the engine...LOL

Just to be clear on your position...its over kill on a street engine and has no real benifits except as insurance for the occassional missed hi rev shift, and not pose a problem for daily driving...

Thanks

Prop
Prop

Willy,

I think that is spot on...

I used all "gold standard parts" and stayed away from the cheap stuff...(except for the valves which should have been rimflows, I used generic knock offs)And I spec'd everything 3-4 times instead of a fast eyeball with the micro.

My guess Is Onno built the same way I did, Strength and longevity 1st and hi-performance 2nd, most likely the reverse of what a true track race engine is.

Prop
Prop

Prop

You are right, I cannot see the point on a road engine to be honest Race use only for me. I would rather spend the money on some other goodies. For instance many people still seem to fit repro cams when billet ones, especially the lobe drilled A series ones are far superior in terms of life and bhp. It strikes me people will ignore the important basic things to chase the more exotic ones. The 'proper' Midget 1275 engine is damn nigh bullet proof in original form.

Peter
P Burgess

>>>>>>>It strikes me people will ignore the important basic things to chase the more exotic ones. The 'proper' Midget 1275 engine is damn nigh bullet proof in original form.<<<<<<<<

Peter...

Trust me, Im an expert on this topic!!! What you discribe is called "Unique Cool Factor Syndrom", Meaning you want something a cut above everyone else thats also rare and hard to obtain or hard to build. And yes I suffer greatly from this afflection. If it werent for people with this afflection id imagine the 1275 would have died out years ago...LOL

Prop...Minimania! heck I should have just purchased the company...it would have been cheaper then the parts
Prop

Prop
Stop comparing me with you!
I have a driving midget.

Willy
That had crossed my mind.
And figured that if i did it right it would not do anny harm and might have a few benifits.

Wanted a bomb proof botom end and it works great
ready for anny future head or cam change
Onno Könemann

Hi Onno

I hope it will be a billet cam :)

What sort of cam were you thinking of using? I know a lot of people are using Swiftune specials but I hear a few people grumbling a little about valve train noise and early cam/follower wear on some profiles with high lift rockers.

Peter
P Burgess

HUH Onno,

Hate to tell ya this But your agreeing with me. Not the other way around...I was just being curtious and acknowledging you you siding with me...LOL

Peter,

I havent heard that on the swiftune products, I have the sw5-07 on 1.5 lift ratios plus the lifters and springs that came with the kit...what should I be looking for and how far off in miles can i expect issues...Anything I can do to prevent valve train issues your refering to.


Prop...Grasshooper onno, under my toulage youve come so far, Im proud to call you my student.
Prop

Hi Prop

Just keep am eye on things and suck it and see.

Peter
P Burgess

Thinking about upgrading to a RE13 ultimate torque (or pure preformance??)our friend CK likes so much.
In combination with a titan belt drive.
But always open to sugestions.

now it has a old 731 cam with std timing gear 1.5 roler rockers a 45 weber and for ease of mainatance there is a 123 ignition to be fitted.
Some hate the cam but it works.

got a MD310 (in bad state) and a verry pointy mistery cam as a surprise with a bunch of parts.
But i am not feeling lucky enough to try those in a street car.

Maybe in the future when i have my planned Injection and ignition ECU to compensate for the rough idle
Onno Könemann

There was a time when my Sprite's road engine that had never been raced or rallied or track dayed regularly saw 7500rpm. Once by mistake that engine saw 8,200rpm. It was strapped.

American's generally don't see to push their road going Spridgets anything like as hard as I think Brits do or I do/did mine.

Daniel Thirteen-Twelve

7500 in anny gear is just to damn risky with all those speed camera's here ;)

And 7500 is just not where the power is with My cam tops out at 7000 max and shifting earlyer (6500) still keeps you easy in the power band.
Though when i'm in a sprint i do not look at my revcounter every second so who knows where my engine has gone ;)
Onno Könemann

Curious Onno,

Being that yo are going to do a fuel injection system Then Id imagine you did consider the Ford edis egnition system .... the one with the timming trigger on the crankshaft pulley, instead of the timming in the dist. what made yo go the traditional route instead of the edis

Personally I did consider the edis system but it was to advanced for my personal understanding...Perhaps down the road I may convert.

Like I said, Im just curious or if you had inside info that it maybe a bad mod on the 1275

Thanks

Prop...Now look whos the student.

Prop

American's generally don't see to push their road going Spridgets anything like as hard as I think Brits do or I do/did mine.

Danial,

I think you are more right then you know, esp. here in the midwest. I cant say much for the east and west coast

here are some of the reasons I belive what you say is true

1. lots of cops, which means higher insurance rates

2. Fewer places to actually open it up and drive fast, our back 2 lane roads are the best (at 2am) but during normal hours they are packed with farmer jones wife with her handicap sticker moesing along at 35mph and a town every 20 miles with a speed trap of 15mph, then there are all the combines and farm tractors on the road, so everyone drives the 4 and 6 lane intrestate... which is straighter then a penny nail, and jusst as boring to drive

3. you break it you fix it! unless your lucky enough to live in a place like st. louis Mo which has john mangles ... if your like me, then he is 3-4 hours away one way depending on traffic, then your doing all your own work as the tech is to old for modern day shops...of which many have never seen points and condensers...let alone Su carbs

4. we dont have alot of organised racing events that are euro style... here its all dirt circle track nascar type racing...no road racing that im aware at least not in my back yard. were so hick for the SCCA, but then I dont know of anyone that would join such a sissy group...To many rules and wat to much politics not enough racing is my in the SCCA IMHO.

Prop
Prop

Fit a rev limiter, the soft cut on mine comes in at 7K & i regularly see that in the lower gears.
Brad 1380

Hi Prop

I was helping a customer set up his mega squirt (XJS) last week on my new rolling road which is, at last, up and running. The eddy brake pau made it fairly straight forward mapping the sites for fuelling. To be honest we aimed at a CO of 5% everywhere as it was a race car. Power runs are acheived in very short time. The most accurate bhp logging is by energy storage flywheel I am told. This involves timing the acceleration of a known weight flywheel. At 280 bhp at the wheels the Jag span the rollers up pdq. The Midgets, Minis and MGBs we have run a steadier ! The software generates bhp and torque figures corrected every 50 rpm......too much info I think :)

Peter
P Burgess

Peter, do you have experience of setting up advance for Megajolt? I have installed this on my 1380, it will need a rolling road session to get the fuelling right on the DCOE, I'd rather use someone who can also adjust the timing via the laptop.

Mat
Tarquin

Hi Mat

If you can do the laptop work, I will tell you what to set the timing to! I am happy to do the testing. In the past this has worked well. I am not interested in learning all the different programmeable systems, it takes me all my computer skills to work with the software with the new rolling road! Mapping has worked well on many occasions with the owner altering the settings under my guidance...teamwork.

The Weber should be a doddle with the functions of our eddy brake pau, we are getting lightening fast sampling rates.

Mind you I miss the old mph and bhp analogue dials, the new system displays dials on the screen then flips to a power graph pretty instantaneously, at which point we all crowd round the screen :)

Peter
P Burgess

Peter
Just a tiddle off subject but I have been offered a 50mm Weber and would need to get some different chokes for it, probably 44mm. Do you know of a reliable stockist of parts for these that I can do an order with .
Thanks Willy
WilliamRevit

Hi Willy

What are you running it on? You couls try Aldon Automotive in the West Midlands, they are pretty helpful for us.

Peter
P Burgess

Prop
why do you assume it is going to stay on a distr.
complete ecu so that includes programable ignition.
That is where the real benifit is
Onno Könemann

Onno,

Sorry... I mis understood, I thought you where going with the 123 Dissy as your ignition source

Prop

Peter,
If you and tarq can work something out, is there any chance you guys can video the project day and post on youtube, Id love to see that afternoon of tech day, as Im sure others would also.

Prop...I wish we had rolling roads for midgets in my neck of the woods
Prop

Hi Prop

I am only 5foot 4 inch, hence a midget, are you short too, hence wishing for rolling roads for midgets in your area?

Peter
P Burgess

Peter, sounds interesting. I'll get myself sorted on the laptop then have a trip down. WOn't be for a month or so though.
Tarquin

Hi Tarquin

I think you will enjoy all the stuff that comes from the dyno runs, very informative.

Peter
P Burgess

Peter
Yeah thanks I'll give Aldon's a try.
The guy with this carb reckons it came off an old Aston years ago -- Cheers Willy
WilliamRevit

Prop, there are plenty of chassis dynos in your area. None with techs that understand midgets? I assumed the same thing too. Then I walked into the lobby of one of the garages and there were a bunch of SCCA pictures on the wall from the 80's. The owner used to build/race sprites. Ask around, you may be surprised.
Trevor Jessie

You may have a point trevor,

perhaps in st. louis or Kansas city...I havent looked at all in those areas, the only dyno I I know of is at lake of the ozarks, just down the road from me, and they mainly do rice burners, american mucscle hot rods, and dirt track circle cars

I know they could do a basic hook up and do a run, but im not really sure if it could tell me much...Still when I do get it running with over 5000 miles on the clock I am planning on having them give it a run just to see what the numbers say, if for no ther reason to brag and gloat about....LOL.

Peter,

LOL...Good one, I saw that last night, but it only made scence just now...LOL


Prop
Prop

Willy, I have a guy in Brisbane that stocks Weber and Dellorto jets....

Mark.
M T Boldry

Hi Mark
Thanks for thinking of me but I'm all sorted now. I can't believe how much cheaper the weber bits are compared to the Dellorto. Found a pair of chokes for $25ea.US Thanks again Willy
WilliamRevit

When I spoke to Graham Russell (who builds many mini race engines here and has a good reputation) about building a fairly serious supercharged engine for my Midget he said not to worry about strapping the centre main, he believed it was a waste of time and money.
AndrewF

Peter B

What you said below is good news for us spridget owners (those with the thick flange block anyway) but it flies in the face of all that we have told for years; as in the A + block & heads are the best ones to use. I wonder could you expand on this statement:-

"I do know that the Midget engine is far stronger than the A+ engine and I try to steer folk away from the A+ heads and engines whenever I can"

Ian
Ian Webb '73 GAN5

This thread was discussed between 10/07/2010 and 19/07/2010

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