Why does my oil seal keep failing?

After adjusting my final drive chain (possibly a bit on the tight side) I had an oil leak from the primary chaincase and the sleeve gear oil seal. I replaced the sleeve gear oil seal and the primary chaincase oil seal (it's on a MK3 so a proper seal is fitted).

All was well for about the first 300 miles and then suddenly an oil leak, which I isolated to be coming from the seal in the chaincase. Pic taken with a mirror.



I am suprised that it has failed so soon especially after never having one fail before, and have therefore done some further checks. What I have found is that the chaincase oil seal fitting does not sit square to the sleeve gear shaft where the seal fits. It sits about 2.5mm out, on a line drawn from the centre point down towards the 5 o'clock position. (Sorry about using millimetres). The 6 and 4 refer to the gap in mm between the sleeve gear and the chaincase and are the widest and narrowest points.



As it is fitted on a MK3 there is no gearbox adjustment to get the shaft slightly more centralised. Possibly if I refit it all AGAIN there may be no more problems, and as it has never caused a problem before with the same engine plates, but I am puzzled as to what is goung on :?: I also realise that probably all of the shafts are probably out of square to the chaincases. Do you think that this could be the main cause of my problems?

Any thoughts?

That amount of mis-alignment would certainly cause quick seal failure. The only time I have seen that much mis-alignment was when the engine to cradle bolts had been run loose and the holes were worn egg-shaped. You certainly need to loosen the engine to cradle bolts and move that back to where it is concentric.
If the bolts are not a close fit from the engine to the cradle I would ream them oversize and install 10mm bolts. Simply lining them up and tightening them will hold for a little bit but not long.
You need to use good grade bolts from the rear of the engine to the cradle. Using stainless bolts in that application is asking for trouble. [unless they are special high grade stainless bolts $$$] Jim

Well I have seen this much mis-alignment and failing seal - soon after I found my primary chain adjust was too dam tight when at full thermal expansion, to learn it only takes once too tight event to tweak the whole drive chain, which if you don't go completely though and just fix the first obvious thing found, then too dam soon later the next in priory fault will fail, usually away from home, till ya have replaced it all back good as new with the multiple gaps of serial repair frustrations, ugh.

Better check crank end run out now too and hope ya don't go ugh, like I have.

comnoz wrote;

install engine to cradle bolts had been run loose and the holes were worn egg-shaped..

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The rear engine bolts are a nice loose fit in the holes, but the engine cradle holes dont look out of round. I'll investigate this area a bit more to see if this has contributed to the misalignment.

Thanks for the advice. I'd never thought to look at this area.

hoobot wrote;

once too tight event to tweak the whole drive chain

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I did have the final drive chain a bit tight, but whether or not that has caused the misalignment??

This seems to be a common problem on MKIII, I read somewhere that the cradle will be stamped with the engine number. It is suggested that this was done in build so that seal alignment was correct for that build. Remember that alignment is best done with the bike off the centre or side stand, a pain I know, but loosening off and check as you re-tightening you should be able to get the gearbox to align centrally with the seal. Also. It is worth checking the quality of the seal, having recently purchased two seals for my MKIII kickstart shaft from two retailers who claim to sell genuine ANIL parts, both fitted but failed instantly. Only when ANIL sent me one was the difference in quality obvious.

Also can be first hint the rear wheel bearings are toasting and/or the dummy axle is giving way - ugh.