How to make sure your sump gasket seals

[JohnLiddle]

Amongst other tasks I have been undertaking on my daughter's 1098, I have been working my way through the oil leaks (wrong ill-fitting oil filler cap, burst diaphragm in oil pressure switch) and finally the remaining task of the sump gasket (leaking at the usual place, the rear cork seal).

Having read a great many threads on this subject on the message board, I was not looking forward to much success, but in the end I developed a method which worked and which I thought might be of some interest to others facing this job.

I had a couple of gasket sets with the cork seals (I bought 2 in case I cocked one up) and when I looked at the cork, it appeared to be far too long for the channel in which it sits. I could see that if left protruding in this way, there was a high chance that the seal would “spread” sideways as the sump was bolted up and become nipped between the sump and block faces, thus preventing a good seal.

I knew that the Haynes manual talked about them being trimmed until they were proud of the surface by 1/16”, but the various threads I had read suggested to me that if trimmed like this, the seal was likely to fail. Seeking guidance, I ‘phoned the supplier (Charlie Ware) and asked if I should trim the length. Certainly not! Came the reply, they are the right length – coat them with grease and they will push in.

So, I coated one with grease and lo and behold, with sustained thumb pressure on each end of the seal (being careful to press along the axis of the seal to prevent it moving sideways at the top of the channel), it did squash into the recess. However, it also popped back out again when the thumb pressure was released!

I had already decided that I would use a sealant (Hylomar Blue) to augment the sealing of the gaskets and I decided to extend this to the cork seals, on the basis that although Hylomar does not set hard, it does become very thick and sticky and I hoped it might retain the cork seal in the channel for long enough to fit the sump without the cork popping out too proud and running the risk of it spreading sideways and preventing the sump from sitting down properly.

So I cleaned the grease off the channel, coated a new cork seal with Hylomar and pressed it in with the thumbs as before. I held it there for a short time, and when I released the pressure, the seal still rose up out of the channel, but much more slowly than before, due to the viscosity and adhesion of the Hylomar. I then decided that the seal needed to be confined to the channel for a much longer period of time to allow the Hylomar to more or less set before the pressure was released.

I therefore clamped a piece of wood across the ends of the seal, which compressed the cork until the ends were flush with the sump face and left it to set. Other commitments meant that I did not get back onto the job until the next day and when I released the pressure, although the seal still moved, it stayed far enough down in the channel to make for sensible sump fitment – the ends protruded by about 1/16”.

So I re-clamped that end of the sump and repeated the method at the other end. While it was setting, I made sure everything else was ready – cleaned up the bolts and the tapped holes in the sump etc. The next day, I released both sets of clamps, applied Hylomar to the gaskets, the curved faces of the cork seals and a generous blob on the end of the cork seal where the gasket sits on top of it. I fitted the sump and tightened the bolts to 5 nm (about 3.6 lb ft) with the dinky new low range torque wrench I had bought just for the job. I then went round the bolts again at the same setting until I was sure they were evenly tightened to that setting. I then set the wrench to 9 nm (6.6 lb ft) and put the bolts up to their final torque setting, again going round and round until they were all evenly tight.

I left it alone for half an hour and then re-checked the bolts – all had relaxed to some degree, with the ones adjacent to the cork gaskets relaxing the most. Having nipped them up the right setting again, I left it for an hour and then re-checked – again there was a small amount of relaxation with the bolts near the cork gaskets being the worst. Another hour’s wait showed no further relaxation, so I refilled the sump.

The proof of the pudding of course is running the engine – well, several days on and after a 90 mph (on the clock!) dash down the motorway later, the outside of the sump is as dry as a bone – job done!

Lessons learned:-
1. Don’t cut your cork seals
2. Sealant is not necessarily a bad thing
3. Don’t assume that because you have initially tightened the sump bolts to the right torque you have finished the job.

I hope this helps others tackling this job.

John Liddle, Backwell, North Somerset – “Where the cider apples grow”