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Leaky chaincase

Submitted by john_carter on Fri, 14/07/2023
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The primary chaincase on my '36 Model 18 leaks like a sieve so I've managed thus far by spraying chain lube through the inspection hole and hoping for the best. I've tried a new rubber seal and red rubber grease but the gap between the front and rear chaincase cover is just too big especially at the bottom where a good seal is needed most. I've tried a bit of fettling on the front case but it's not been successful. I'm now going to remove both front and rear cases and try and 'coax' them into mating on the bench before I reinstall. Is getting an oil tight seal a realistic goal?  Any tips?

Thanks - John

Submitted by neil_wyatt on Fri, 14/07/2023

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In my  experience the biggest culprit is over tightening the centre nut. I have always found that leaving two threads showing is about the right tension.

Unfortunately, over tightening can cause distortion, so to un distort is the starting point.

Normally, SAE 20 or 'Castrol light' would be the correct oii BUT I note that the 37 16h  specifies SEA 50 (Thick, yes I know) but worth experimenting with.

There are lots of other suggestions given in previous threads on this topic such as sealents etc.

That said, expect to top up once in a while, nature of the beast. Good luck.

Submitted by paul_standeven on Fri, 14/07/2023

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- is that of the footrest mount, or the inside of the nut?  I used to have my chaincase nicely oil tight, but of late, the harder I try, the worse it gets....  I aimed for the nut to be level with the end of the threads of the foot-rest mount, using Loctite 515 on the rubber.  It was a fail....

Submitted by richard_dunn on Sat, 15/07/2023

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I am having the same problem right  now with my 650ss , I've bought a new sealing rubber too , from RGM , it appears to have a slight taper and a small lip on one edge , with the apparent taper it's thicker than the old one which is srtaight and the case goes on fully but I can't even start the big nut on the thread now ,, I'm loathed to use the old one after buying a new one .

  a couple of people say they've fettled the rubber slightly which I'm reluctant to do and I'm not touching  the case ! , another suggestion was to leave the rubbber seal in boilng water to make it more plieable , that's my next trial but not hopefull  ,, if you have any success let me know  

EDIT,,,,,,,,, Getting the rubber hot in boiling water first doesn't work ,  

Submitted by john_carter on Sat, 15/07/2023

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Thanks to all for your comments and advice. Richard, I'll let you know if I have any success. Having gone down the rubber fettling route once before (result: buying another one) I would recommend you persevere with an unmolested one. Good luck.

Submitted by tony_wood on Sun, 16/07/2023

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Hi. I bought a new band from AN for my 99 and it was a good tight fit around the inner cover but like you I couldn’t get the outer to go fully home. I found that if I used a very thin steel washer over the footpeg tube instead of the correct thick one, I could just start the nut on the threads. Then I tightened the nut a little at a time, gently thumping around the perimeter of the outer case with the heel of my hand as I went. I tightened the nut to the ‘two threads showing’ mark and left it like that overnight. Next day I removed the nut and washer and the outer cover stayed in place long enough to get the correct thick washer and nut fitted so that I could tighten it all to the correct setting. 
You may (or may not( be able to use the same dodge - good luck.

Tony

 



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