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MG MGB Technical - Bump Stop & Fuel Breather Pipe - silly questions

Guys,

Silly Question no 1
How is the bump stop (as per photo) fixed to the chassis rail?
Do i just pull it off or twist it ?
I don't want to wreck it in the process.
I intend to re-use what's on the car. (Suppliers show either a replacement bump stop or one complete with a bracket).

Silly Question no 2

The plastic fuel breather pipe on a late UK RB car runs from the top of the tank by the filler tube & into the chassis rail until it appears again through the side of the rail just forward from the rear wheel arch & then traces back to the fuel pump.
Suppliers list the later tubing which is a larger diameter than earlier cars , but also show a T piece. Looking under the car , i can't see this T piece , but don't want to pull the old one out from the side of the chassis rail & find i have jammed something. If the tube just runs on it's own from the boot area to where it comes out through a grommet then other than a bit of fiddling i should be able to thread a new one in. (Or am i missing something - what's the t piece for)?

Cheers
Charles



Charles9

ETA: I've just realised you might not be referring to the fuel pump, but if you are -

Charles,
if you've done away with the SU (labelled but not made by?) fuel pump then you may not need those tubes anyway, they're to allow air to be moved inside the pump (more modern pumps don't require them).

I don't know their routing or where they terminate on the B's but on the Spridgets they go to inside of the boot to avoid moisture and debris, to avoid blockage from crud, wet, that goes under the car.

I'd guess the T-piece is to stop debris too and I suppose using a insert terminal on the tubing reduces the exit/entrance aperture so having a T gives two openings instead of only one on an elbow (or more likely the stock they had (ordered) Ts and not elbows.

The parts list shows clips, I don't know where they are, but anyway brittle old dirty tubing I've always found doesn't move easily, even the new tubing I coat with GT85 to get through grommets.

Nigel Atkins

Hi Nigel,

Thanks for your reply re Silly Question no 2.

I am still using the original pump as it came out from the factory & as purchased new by me.
(Using your approach "if it ain't broke don't mess with it") . I rather like the clicking of the pump when i switch on etc. etc. When it does eventually pack in ,then i will make a decision as whether to change to a more modern solid state electronic one.

The plastic breather pipe is looking a bit tired & as i am re-furbishing underneath (as per my recent threads) with the car up on 4 axle stands it is an opportune moment to deal with it.

Hopefully someone can add a bit more clarification as to the routing & the possible use of the T Piece, as it is not referred to in the workshop manual or Haynes etc.

Cheers

Charles


Charles9

Question NO.1:-
A combination of pulling and twisting should remove it. For refitting, a dab of silicon grease helps it to slide over the spigot.
Dave O'Neill 2

Thanks Dave,

"Simples" then as they say in a well known advert!

Cheers

Charles
Charles9

Question 1 they just pull off, but a bugger to get back on. Lubricate with washing up liquid or green Swarfega.

Question 2, the T piece is located in the boot by the bulkhead towards the Rh side. It will be sat in a grommet.

Colin
Colin Parkinson

Thanks Colin,
As long as the bump stops are easier to get back on rather than than the oil cooler hoses through the rad support then I'm quids in!
Cheers
Charles
Charles9

Charles,
when completed we will of course need photos of this show condition underside.

The vent/breather tubing sounds like they're the same place as in Spridgets. Here's a tip you can have for free, remove the T before pulling the tubing from under the car. :)

I didn't really know with the bumper stop so left it, but I'd give it a quick wipe over to clear crud and then spray with GT85 (PTFE) or rubber/nylon lubricant (silicone) just to help ease it out in case it might break and leave a part of it stuck in and difficult to get out.

Nigel Atkins

Nigel,
I'm not aiming for a show room finish, just a prudent preservation exercise to keep the tin worm away. (Impossible really, but at least slow it down).
I will post something up when i have finished.
Cheers
Charles
Charles9

Charles,
I was joking. Don't waste time taking photos of the underside (unless you're taking things apart and want to know where they went before).
Nigel Atkins

Nigel,
I realise that you are joking!
I try to remember to always take photos before & aftef both so i can check that i am putting stuff back correctly & as a record for myself of "before & after" so i can give myself a "pat on the back" when all done & as a record of the car's history having had it from new.
Cheers,
Charles
Charles9

People have had to resort to clamps to try to pull bump-stops on or blocks of wood between the bump-stop and axle and jacking the car down onto them http://www.mgb-stuff.org.uk/saga20.htm. I've not had to do those, but it sounds worse than the oil cooler hoses I've done.


My 75 V8 has the pump body vent pipe ending in a Tee beside the pump as in image 1, but Steve Livesley's 75 roadster (and I suspect later models) has it going to a nipple on the side of the chassis rail as in image 2. As far as I know it vents to atmosphere from there i.e. no other pipes or Tee.

You say "The plastic fuel breather pipe on a late UK RB car runs from the top of the tank by the filler tube" but again as far as I know only North American tanks were vented, going forward to the charcoal canister in the engine compartment, UK cars always had a vented fuel filler cap. I at least would like to see pictures of this tube.



paulh4

Hi Paul,

Bump Stops
Having read the detail on getting them back on & i know that your experience with the oil cooler hoses was similar to mine I'm going to leave well alone there (should please Nigel- i do agree with him about regular maintenance though)!

Breather tubing

The second image re Steve's roadster doesn't appear to have been posted up.
I have attached photos of mine which show the pipe coming out of the chassis rail which then traces back to the pump , but the lack of the other end appearing by the pump cover in the boot.
(The yellow blob you see to the right on the ledge is a rubber boot i put over the sharp end of a self tapper that the guy who fitted copper & new rubber fuel lines placed an additional clip there; possibly due to reinforced rubber fuel lines needing to be held in place compared to the original "lawn mower" type hoses that were much more flexible & certainly easier to fit & seal with the spring clips).
I'm loathe to start pulling all the stuck down carpet out of the inner wing of the boot, which i took some time to fit well unless the tubing is routed inside in that area somewhere - there is nothing round the large filler rubber!

Cheers

Charles






Charles9

As yes image 2 got forgotten, here now, but it's basically the same as your second one.

Your first one showing the tubing sticking up by the pump is probably like my 75 V8 in image 2, but the tubing has been fed outside the cover. It could be said that mine being bent over like that is pinched closed, but it's never caused a problem, and early pumps didn't have any vents.

But it's the one "from the top of the tank by the filler tube" that I wanted to see.

Incidentally you asked what the Tees were for - possibly to prevent debris dropping down the open ends of the vertical tubes where they came up through the horizontal panel in earlier cars which could block them. Which may be why my pump-end tube goes down inside the cover instead of up outside it. And/or to stop the tubing dropping back down, although at one point one of the tubes was behind a harness clip so was unlikely to have dropped back anyway.






paulh4

Hi Paul,

The reason i thought the breather tube must be near the fuel filler pipe is due to the reference point 7 in the R O Manual AKM 4070 (1978). In my car there was a grommet in a hole behind the filler pipe. I covered it with insulation tape some years ago as it was loose fitting & I wanted to minimise any damp getting in or stray exhaust or fuel fumes.

Like you Paul i haven't had any fuel supply issues (over 40 Years) whether i use the original vented cap or vented after market lockable versions.

That still leaves the question of what happens to the breather tube after it disappears into the chassis leg.

Does anyone else have a late RB who knows, or could check in their boots?

Cheers

Charles






Charles9

That page refers to North America spec when the vented tank.

Originally part of the rear harness (two wires) went out of the boot floor by the filler pipe and forwards to the tank sender.

On rubber bumper cars the routing changed so that the (now) single tank sender wire came under the floor from by the pump and back to the sender, and the boot hole blanked off with a plastic grommet.

TBC






paulh4

Continued:

North American spec had several variations of emissions plumbing, tanks having the vent pipe in that same position as shown here.

The pump breather just ends at the chassis rail, there are dozens of places in that which will vent to atmosphere with minimal chances (bar river wading) of water and dirt getting sucked into the pump. I can't see the point of moving it let alone lower and to the 'outside', but there we are.

You have to be careful to fit a vented cap in the UK - locking or non-locking, as with a non-vented the tank can't draw in air as fuel is used and it will starve the carbs.



paulh4

Hi Paul,

Thanks for your insight. The good book doesn't make that clear in the section i took the photo from.It is only on the next section dealing with the different fuel filler neck where it refers to variances for USA & Canada.

That suggests i can just pull the plastic pipe & grommet away from the chassis leg & replace?

Over the years,whether it be the original tank or the relatively recent replacement with careful attention to the condition of the rubber fuel lines connected to the copper lines that has only experienced warm weather conditions , i have always smelt the slightest smell / trace of fuel in the boot. May be that is the result of the breather tube exiting into the chassis leg.

Cheers

Charles
Charles9

I didn't have any difficulty refitting the bump stops, although they were the originals, not modern replacements.

The spigot did have shiny paint on it and I used some silicon grease on the rubber, and it pushed on by hand.





Dave O'Neill 2

Charles,
sorry but I must start with an admonishment, the 'good book' is the Driver's Handbook not Workshop or Repair Manual, the good book is about prevention not repair. ;)

I'm very happy to leave things well alone that don't need touching and I'm happy for others to do more and more regular maintenance than I do.

Yes, taking a photo first and putting it up for others to point out any mistakes made by previous workers on the car is a good idea rather copying the mistakes.
Nigel Atkins

I don't know if this is germane to the discussion about venting the fuel tank but it is very difficult to fill the tank in my '72 MGB. I've never inspected to see if the tank is vented, if the venting is blocked or if this could have anything to do with the difficulty in filling the tank.

If I pump VERY slowly I can get the tank full but if I pump at any rate more than VERY slowly the fuel backs up in the filler tube and shuts off the nozzle. This starts happening when the tank is about 2/3s full.

Any thoughts on whether my issue is related to the issues in this thread will be appreciated.

Thanks.

Jud



J K Chapin

Jud,
it depends on the type of pump nozzle you have out your way, if they're like ours with covering to enclose the filler aperture to prevent the fumes escaping then I find I can only fill my tank on the Spridget by holding the nozzle out so the aperture isn't enclosed. This of course isn't the correct thing to do but it's what I do to get the tank full and in a reasonable time.
Nigel Atkins

Dave,

Bump Stops

Thanks for that. Paul's comments rather put me off.
However, as i am intending to put the originals back on , it may be easier than i thought. We are all aware how the modern rubber replacements of so many parts seem to be much harder e.g. oil cooler grommets , the rubber seal for heater box outlets for the windscreen etc. etc.

Nigel,

I know you call the Driver's Handbook the "good book" . (I agree - very useful for regular maintenance). I should have called the R O M the "really good big book".....!

Jud,

I can't really comment on your issue. I know in the U.K. we have vented caps , but that wouldn't apply when you are filling the tank. I know U.S. & Canada had fuel filler necks with a restrictor & a trap door. (Per the ROM , but not sure if on your age of car). Paul , i am sure may be able to shed some light in your issue.


Cheers

Charles
Charles9

I also re-used my oil cooler hose grommets. No dramas there, either.
Dave O'Neill 2

I don't think I have the trap door (my '77 Ford F-100 had it but it has been removed) and the pump nozzle for the non-ethanol fuel I use doesn't have the skirt so it must be something else. Thanks for the comments.

Jud
J K Chapin

Jud,
on re-reading your post I have addressed the wrong problem but with perhaps the same solution.

Holding the nozzle of the pump out from the filler tube (on our UK pumps) also cuts down on the flow angles from nozzle and filler tube.

If your fill is very slow then could it be your filler tube is out from the usual setting giving more flow angle.

How long would it take you to fill say 6 (US, 5 UK) or 12 (US, 10 UK) gallons?
Nigel Atkins

Charles,
any of the R O M type books are normally the ones you want to avoid really so good isn't an adjective I'd apply, useful yes, good no. ;)

Nigel Atkins

Nigel,

I was joking this time! - albeit i do find AKM 4070 quite useful along with various parts catalogues in helping see how components fit together, never mind certain contributors on u-tube & of course this BBS site.

I agree with you about getting the right angle & how far in the nozzle of the pump is , otherwise the pump cuts out & indeed depending how warm the ambient temperature is.


Cheers

Charles
Charles9

Jud - North American tanks were vented from 1970, and replacements from one manufacturer a while ago were faulty in that the filler neck protruded too far down into the tank. This could mean that in the later stages of filling the air has to escape via the vent and the charcoal canister, which itself could be blocked. There was a separation chamber between the tank and the engine compartment positioned high up by the right-hand rear light.

Some states allow 'desmogging' which has to be done in the right way or you get problems, but probably not the one you are describing.

The other thing is that those tanks were supposed to have a capacity limiting chamber which although you were able to fill up to the neck at the pump, over a short period of time that chamber would slowly fill from the bottom to lower the level in the rest of the tank, to prevent overflow from heat expansion.

I've found more variability in pump nozzles than anything else as far as shutting-off goes. Mostly shoved right in and full flow is fine on both mine, but occasionally I come across one that is over-sensitive.



paulh4

Charles,
the 'good book' reference isn't a serious topic, but I do get a tiny royalty ever internet mention of the Driver's Handbook. :)
Nigel Atkins

As my previous and present petrol tanks on the midget are only 25.5 litres capacity I fill until the fuel is sitting at the very top of the filler tube neck, just behind the back of the petrol filler cap.

To do this I have to be able to see when the petrol gets there, and back flows there so I have to hold the station pump nozzle at the start of the filler tube neck. I would have to hold the nozzle out anyway because once the tank is around half full the pump keeps cutting out even if going slow. I've been doing this for 13 years at various stations but probably do it out of habit, certainly I need to do it at the usual station I fill up at.
Nigel Atkins

Paul, I think you may have hit it with the observation that the filler neck may be too deep into the tank. Once air could not escape through the neck it would have to escape through a restricted, possibly partially blocked, vent tube. This gives me a starting point for addressing this problem this spring.

Thanks.

Jud
J K Chapin

Filling it to the "very top of the filler tube neck, just behind the back of the petrol filler cap" may be OK if you then go off for a decent drive.

Even with the nozzle all the way into the filler on mine and fuel not being visible it has still expanded enough to overflow on a hot day if I drive straight home.

That's why North American tanks were required to have the 'capacity limiting' chamber.

I've read that some American pumps don't allow you fill above the end of the nozzle as the vapour recovery system will suck liquid fuel back as well returning it to the station tank. The amusing thing is that you will be charged for it, of course.
paulh4

My experience is similar to Paul's.
I know that if i brim the tank & then don't drive about 30 miles before puttung the car in the garage, as the rear of the car faces the metal garage door which is in full sun in the afternoon , then i will have fuel dribbling out round the cap.(i open the garage door & then remove the filler cap to reduce the pressure & then replace).
Cheers,
Charles
Charles9

You wealthy types showing off with garage ownership.

It doesn't take long to drop the fuel level and why else would you brim fill unless you're going for a good drive.

I do leave more space in summer and if it's a sunny winter's day and I'm on my way back home 1.5 miles away.

When brim filling the same principle applies as when about to run out of fuel, drive as fast as possible/sensible/legal. For brim filling to reduce the level and when running out to get to the station before the petrol is all used up.

When I get verbal gauge indicated fuel capacity information I say "don't worry darling I'll drive as quickly as possible to a petrol station so we don't run out".
Nigel Atkins

Nigel,
I don't literally fill the tank till i can see it in the filler pipe , but in those glory days of old,if i knew i was going for a long drive to a car meet within the near future, i would fill up in advance to save stopping on the way etc. - its called forward planning. (Saves putting a bottle of fuel additive in the boot as my cylinder head / valves have not been converted to unleaded. .)..
I don't smoke & what some spend on fags would have paid for my garage!
Cheers,
Charles
Charles9

Charles,
I just about brim fill the Midget just about always. When pushing on a bit on tours or runs I'd be thinking about the location of petrol stations after about 125 miles, or 100 if far up north. More recently I've been getting up to 40mpg and in areas where petrol stations are more plentiful so not so bothered getting home with just fumes left.

I try to fill up when it's cooler to get more for my money.

I've never smoked either, where did I go wrong. :)
Nigel Atkins

"I try to fill up when it's cooler to get more for my money."

You jest of course. I'm sure you know that the fuel in underground tanks has a very stable temperature, that's why it expands and overflows in a car tank on a hot day.
paulh4

Yes but what about the the line and hose above ground, there must be a good few pints there, every little helps, and it does mean you can get more in your car's tank and filler tube which are both above ground to allow for what is burnt off from station to destination.

Similar problem to these pubs that have too many guest ales on handpump, over warm ale sitting in the pump and lines too long - don't get me going on this subject!

I do allow for future heat and expansion but I have been caught out as it can sometimes be very difficult to see the clear liquid in the dark filler neck and solar gain in winter can be surprisingly very high (something for the grand and great grandchildren to sort out). I did once have the petrol lapping at the back of the filler cap, luckily it was straight out on to 50mph dual and the NSL dual within half a mile on a warm engine, I did go round the large roundabout twice just to be sure of using the excess.

Nigel Atkins

Guys,

An update on bump stops & fuel breather.

The bump stops came off with a bit of swearing , but just by hand without resort to any form of levering with big screwdrivers etc. Once the spigots were painted up & the original bump stops cleaned up & treated with vinyl rubber restorer , they were replaced quite easily using a little grease on the spigots & rims of the rubber.

I was intending to replace the breather pipe to the fuel pump.(On e end simply goes into the chassis rail close to the ARB pivot bolt mounting. The other end is attached to a port on the body of the fuel pump on the underneath just where the body enters the rubber seal into the boot.
I removed the fuel pump cover in the boot to find no breather pipe attached to the points cover. (This is different from Paul's photo, but seems to match the illustration in the ROM AKM 4070 1978).
There appears therefore to be yet a further change to how breathing was dealt with in the last couple of years of production. Maybe this is why i get a trace of fuel smell in the boot when it has been closed for a while. (Fuel tank was replaced during my ownership with no exposure to winter weather etc.) Is it worth putting in an additional breather pipe

Needless to say , i shall have to wait till lock down finishes to get some help from a classic car neighbour to assist in pushing the old pump out to at least replace the existing breather as it is tight up against the bulkhead underneath & gripped tightly by the rubber seal.

Cheers,
Charles



Charles9

You shouldn't be getting any fuel smell from either of the breathers, that would imply the diaphragm was leaking. It could be from the filler pipe hoses not tightened enough to seal, but running a temporary breather tube from the port on the end of the pump to somewhere outside, somehow, might help prove it one way or the other.

There is a vapour line shown right by the filler pipe as mentioned last month, but that should only be on North American spec cars.

I have AKM4070 and see the breather on the pump, but haven't spotted where it shows it going to - page or section number?

Also how breathing changed in the last couple of years.
paulh4

Hi Paul,

Like you i couldn't find any trace in AKM 4070 as to where the breather pipe should go. On my car which is as it came out of the factory it goes to the chassis rail by the ARB pivot as per my photo on the 14 Jan 10.49.
Strange how they just stopped installing one , but the pump still has a port....

I presume you mean my main tank filler pipe may not be tightly secured at either the petrol cap end or the tank end? I haven't checked that since the replacement tank was installed some years ago...

Cheers

Charles
Charles9

Well done Charles.

I can only think the tubes are used and routed to ensure the diaphragm inlet/outlet terminals are in a position where they can't be covered by anything, such as something placed in the boot, and not collect moisture.

Seems strange to need such elaborate arrangements but perhaps they found the diaphragms on those pumps could get so feeble that a slight bit of pressure against them would overtax them. :)

Nigel Atkins

Hi Paul,

Where does your points vent tube go in your second photo of January 14th 12.48 or is it just dangling behind the box? The T piece in your photo refers to the diaphragm vent.
I'm minded to run a tube round the inside edge of the boot from the points vent to the grommet in the boot floor behind the main filler pipe as per my 2nd photo of 14th Jan at 14.21

Charles
Charles9

My points vent tube does just dangle behind the metal cover. I can't remember where that tube came from, the car came to me with a Moprod pump with no vents that started giving trouble so I replaced it with the repaired one that came off my roadster.

You could run it through that bung by the filler tube, but really if there is any suspicion of the diaphragm leaking and fumes getting into the boot that way the pump needs to be repaired or replaced.
paulh4

My 79 does NOT have a vent that terminates inside the trunk. There is however, a vent hose attached to a "charcoal" canister. The "charcoal" canister vent hose is then channeled to the intake manifold where it gets mixed with the fuel and consumed.

Cheers

Gary
79 MGB
Gary Hansen

Thanks Guys,

I have "nipped up" the clips surrounding the main filler pipe - i was surprised how slack the top one was , so will have to see if this was the issue.
I may just be confusing the musty smell of 60 -70s cars that i remember from my earlier years with the much cleaner / sterile aroma of today's moderns.
Besides , the roadster boot is tiny & has no ventilation unlike modern saloons with one way vents etc.

Cheers,
Charles
Charles9

Gary's is talking about the tank vent which will have petrol fumes in it, UK cars didn't have that.

Charles's question is about the pump vents, there should not be a fuel smell from those.

CB cars had either one or two pump vents in the boot/trunk, RB cars the same but one of them is under the metal box cover and was always there. It's the other one that on earlier RB cars visibly terminated in a Tee in the boot/trunk, on later cars it goes to a nipple on the chassis rail.
paulh4

This thread was discussed between 13/01/2021 and 04/02/2021

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