MG MGB Technical Bump Stop & Fuel Breather Pipe - silly questions BBS discussion at MG-Cars.net

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

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

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

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 - 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

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

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

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