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Primary chaincase cover fitting problem


I am having problems fitting the primary chaincase cover onto my rebuilt '63 650SS. With the cover in place I do not have any threads on the centre footrest sleeve exposed to screw on the centre nut. The case appears to be fully seated onto the rubber washer. It seems as if the flanged left hand footrest sleeve with the chaincase threads on is too short. The chaincase fitted satisfactorily before the rebuild. I have replaced the felt washer between the rear chaincase and footrest flange with a new one .This seems thicker than the old one that it replaced but that is probably because the old one had 40  years of compression and oil on it. I have also replaced the old RM 19 alternator stator with a new encapsulated RM 21 and put on a new clutch outer drum but it doesn't seem as if these are stopping the chaincase cover from fitting. Otherwise the parts are as they were when the bike was dismantled. I could remove the felt washer and gain 5mm or so but this might not be enough and would possibly encourage an oil leak. 

Am I doing something silly and has anyone any idea as to what I can do to get things to fit. Attaching the chaincase is about the last thing I need to do before trying to start the bike for the first time in 35 years.

I have attached some pics of the problem.


Your Pic 4 shows two items that could be preventing the outer from seating properly.

The alternator wire need to be much flatter.  Use a hot air gun to soften the plastic and change the run.

Underside I notice a sidestand and protruding nut.  Is the nut fouling the outer?


I had the same trouble with a twin.  The new stator with  the cable exit on the outside  is replacing one which had the cable exit on the inside . This may be causing the issue. I have also read that the alternator will not perform correctly like this. I dont think this is true but the cable is vulnerable to wear on the cover. . The clutch adjuster can interfere with the cover , Remove the clutch cable from the box and then adjust the center screw in all the way and back off half a turn . You may then find the cable is too short, cut off a bit of the outer or get a longer cable , Trust me on this ,you can get a much better clutch. Other trouble can be the prop stand lug (trim the outer cover) and the engine sprocket not seating fully due to a misspositioned key . An extra pair of hands to push on the cover may help.As a last resort remove the chrome washer and seal and pull the cover on with the nut  and some bumps with a rubber hammer,then remove nut and refit the parts.    Hi Phil ,our posts crossed !.



dont know if its how the camera has caught it, but the footrest tube with the thread looks to be off centre




It also appears that there is NO clearance  between the Stator and rotor. This (if true) will cause big trouble. Contact-heat-siezing!! There needs to be an 8 thou gap min all the way round!

The other thought, if/when the case was painted? Was it 'straightened'? Often the centre that gets pushed in with the large chrome nut when fitting, gets pushed back out-too far!

The position of the stator cable is NOT relvant in any way for electricity-BUT if it has a coming together with the chain then end of working, until fixed.


At the risk of stating the blinking obvious, the primary reason for the outer cover not seating properly could be due to the rubber band seal.  In the old days they were tapered in cross-section, so the outer lip was thinner than the inner.  This gave a progressive sealing action and would allow the outer case to move in more than if the rubber had a rectangular cross section the same thickness as the thickest part of the original type.

Having said all that, this shouldn't be the problem if you are using the same rubber band as before. The primary outer case is very susceptible to bending, especially when used for over 50 or 60 years - hence the difficulty making it oil-tight.


Thank you all for your helpful suggestions.

Phil. I too wondered about the stator cable and have tried the cover on with some marker ink on the cable. There doesn't appear to be any contact with either the cable or side-stand nut.

Robert. Same as above the clutch centre nut doesn't appear to be touching the case.

Barry. I also thought that the footrest tube was a bit off centre. I will need to strip down the primary case again to check this and will look at other options before doing this.

Al. There is a gap of between 9-11 thou between the rotor and stator. You are right about the case being straightened a bit before painting and I will give the centre hole a gentle tap with some bodywork hammers to see if I can get a bit more thread showing.

Lionel the rubber seal is the original and was OK before I stripped the bike down.

I will keep you informed as to how I get on


After adjusting the position of the alternator wires using a hair dryer, applying a good amount of red rubber grease and a few taps with a rubber hammer I have managed to get the centre screw onto its thread and tighten it up. I have not yet put oil into the case so don't know if it is oil-tight but thanks to you all for your advice. Hopefully I'll have the bike started in a week or two. Just a few more little jobs to do.


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