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Lister SL3 fuel leak


SweetPromise

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11 hours ago, agg221 said:

This is a good place to start on maintenance. The parts are a sensible size with easy access - not small and fiddly or large and heavy - and you can see what you are doing. Success is pretty self-evident and you are unlikely to set yourself up a whole series of later problems by not quite getting it right. Also, they are fairly cheap if it goes wrong!

 

Some other points which might help, since you can't necessarily assume that the correct fittings have been used to start with. It has been mentioned above that this engine was originally all imperial but is currently a mix of metric and imperial. There are three dimensions on a compression fitting - the OD of the pipe (and the corresponding hole through the top of the compression nut and the olive), the thread on the nut and the dimensions across the hex which determine what size spanner you need. The pipe can be metric or imperial, typically 1/4", 5/16", 3/8", 8mm or 10mm. Bigger fittings are likely to be found on the cooling water system but don't worry about them for the moment. The thread on the nut is likely to be 1/4" BSP or 3/8" BSP. If you measure across the outside of a 1/4" BSP thread it is just over 13mm whereas a 3/8" BSP thread will be just over 16.5mm (I am assuming you are measuring with a ruler rather than verniers so the numbers are approximate, but they are close enough to be confident in what you have).

 

The copper pipe and the corresponding other holes are fairly close between imperial and metric. 1/4" pipe is 6.35mm so you can get 6mm pipe to fit through the hole but you have to excessively crush the olive to create a seal and it doesn't work well. You can't get 1/4" pipe through a 6mm fitting but fortunately these don't turn up too often as they are generally only found in microbore gas plumbing. 5/16" pipe is 7.94mm which is so close to 8mm that it is within the pipe tolerance. These can therefore be interchanged, which is good because genuine 5/16" pipe and fittings are quite difficult to obtain whereas 8mm is relatively easy. 3/8" is 9.5mm so this time you can get it to fit 10mm fittings but it doesn't seal easily. What is more common is people trying to get 10mm pipe through a 3/8" hole which doesn't really work and often ends up with scratches/gouges on the pipe end, causing it to leak. As an aside, in an extreme need this can be dealt with by drilling out the hole in the back of the nut to 10mm and it will then fit but the data imprinted on the nut will then be wrong which could cause a headache for someone down the line. You can't bodge a 3/8" olive onto a 10mm pipe with any hope of success.

 

Another key point to look at is how the seal is actually supposed to be created. There are three distinct options. One is to seal on the olive/nipple - these have a male cone on the outer end, fitting in to a corresponding female cone on the part or the adaptor - check that there is a female cone present otherwise it's the wrong type of fitting and won't seal (note, the other seal on these fittings is to the pipe - an olive seals by compression whereas a nipple is brazed/silver soldered on so the internal of the nut is a female cone for an olive to compress the olive whereas the internal of the nut for a soldered nipple is flat as it just has to push it on to the fitting, the seal having been created by the filler metal). The second option is to seal on the thread. Parallel threads have a leak path all the way up the spiral so fittings designed to seal on the thread are tapered - you can see the slight taper on the male thread and it is easily measured. They can be identified by trying to screw them in and finding they only go so far. Tapered threads are simple but not very efficient on sealing area, so are usually used with PTFE tape. Three turns of tape CLOCKWISE on the thread before insertion is ideal - clockwise because then it winds it tighter as you insert the fitting, rather than trying to unwind it and balling it up. Alternatively there are PTFE pastes such as Black Swan which are easier to use and can also be used on other plumbed parts to make the threads run smoothly. Taper threads act like a wedge so can crack thin castings as has been mentioned above so the third option is a face seal. You can spot these because there will be a flat face on the part, designed to seal with a fibre or copper washer. The face could be either at the bottom of the thread or on the outside. For this to work you need a fitting which has a corresponding flat face - if it is internal the thread needs to be long enough to reach the bottom; if it is external the thread needs to be short enough to not reach the bottom. For an external seal you usually need the hex section to be a bigger size to create a flat area between the hex end and the thread. This third type is a good option on things like the adaptors for your your fuel filter and lift pump for example, although it doesn't look to be what is currently fitted.

 

That's probably enough on fittings before you are bored to death, but it's actually quite simple, there are just several options which have been available over the years and when they get mixed and matched it causes problems, so knowing what you have helps.

 

One other observation - your lift pump has AC visible on it, which I suspect means it was made by AC Delco. Your fuel filter unit looks like it might be a CAV one (check the code on the filter element if you can't find one on the unit itself as that will pull up the unit type the other way around as the filter description will include which units it fits). If they are damaged beyond repair then this should give you a starting point in finding replacements.

 

Alec

Fantastic instructions! Thank you. I feel much more confident in having a go myself.

 

The diagram is very helpful too. Thank you. 

 

I've been having a look today and pulled it apart a bit to get a good look. As far as I can tell, there is no cracking on the housing units of either the pump or filter. The olives on the two new parts do not seem crushed or the pipe crushed either. Before buying new parts, I have borrowed some sealant as has been mentioned and done everything up again just to see if that helps before I go further. The drips seem to have stopped when I last checked... but I'll check again in the morning. 

 

What I did find on the third leak from the pump was interesting. This part was not replaced and appears to be the original fitting as I'm comparing it to the handy diagram posted above. However, I believe the olive and the pipe have been crushed and I suspect this might have been done when the mechanic couldn't stop the leaks and so overtightened all the fittings as it wasn't leaking before he worked in that area. So I think I'll definitely need to replace the pipe, which is 8mm, and the olive here. I watched the drip in this area and it definitely seems to be coming from under the nut where the crushed pipe is. I'm attaching the photo just in case what I think I'm seeing is not what I'm seeing!! 

 

 

IMG_20221130_115045.jpg

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That pipe has been seriously abused. If you look inside the nut, I suspect you will find it does not have a tapered female cone but is flat instead. Note the nut does not have a round section at either end but is hexagonal all the way along which generally indicates a nut designed for a soldered on nipple, which does not need to be crushed to seal, just pushed up against the fitting end hence is internally flat to mate with the outer end of the nipple which has a single cone and a flat land on the back. This would be a likely part of the problem as a flat internal face will distort the olive rather than evenly crush it (which looks to have happened here). It's one of those situations where you can get it to work but it is very sensitive to how tightly it is done up. If there is no cone internally then you either need to use a solder on nipple or replace the nut with a new one which does. If you do decide to go down the soldered on nipple route then it needs to be silver soldered and you either need the short type nipple which does not have a back tube (available but not easy to find), or a nipple and nut, commonly sold together, as that nut looks to have too small a hole to allow the brass tube (socket) to pass through it. I would guess that one is designed for 1/4" tube and was replaced at some previous point. Replacing with a standard compression fitting is much easier,

 

Alec

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One other comment after taking a closer look at the photos. From what I can make out your pre filter is mounted to one side of the engine, but not fitted to it. You then have a short length of solid copper pipe which runs from the filter to the lift pump. If that is the case this length of pipe should be a flex pipe and not solid. This is to allow for engine vibration. Again if this is the case it could certainly cause the leaks in the pipework.

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The AC lift pumps arent meant to have tapered pipe threads screwed in........the correct fittings ,as shown in the drawing,have parallel threads and a cone seat that seals against a matching cone seat in the pump body ......alternative arrangements that are correct are a bulged pipe end and a black rubber grommet  with compression  nuts (Perkins use these)...,or banjo fittings..............any kind of tapered pipe fitting mayl split the weak zamak alloy.

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