Drive side main bearings

Information relating to the Matchless G80 or AJS Model 18 500cc Heavyweight.
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Drive side main bearings

Postby Peter-Karl » Thu Dec 14, 2017 9:06 am

Hi all,
on my AJS 18s I have to re-press the main ball bearings,however, the small ball bearing has no tight fit, I think I'll fit in with Loctite. has one done something like that before ?What kind of sealant is the best? Loctite 648 could be the best but 648 is fixed within 5 minutes so I hardly have time to mount it.
Peter

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Re: Drive side main bearings

Postby cfaber » Fri Dec 15, 2017 4:51 am

Are they the right bearings?

If the bearing seats have been worked out, really you might consider taking the case to a machine shop, having them mill out a flush fit plug and then mill that out to the correct size and position for a good press fit.

But that's how I would handle it.

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Re: Drive side main bearings

Postby Andy51 » Fri Dec 15, 2017 9:11 am

Hi, what year is the engine? In the early/mid 50s singles, there are 2 ball bearings. The outer race is designed to be a looser fit in its housing, while the inner race is much tighter. This allows assembly without pre-loading the outer bearing while still locating crankshaft end wise. How loose is the bearing? If you can turn the outer race in its housing, then it is too loose, but if it is reasonably tight (but less so than the inner bearing) it may be ok. With the crankcase heated in the oven (wait till domestic authority is out!) the bearings should drop in easily. Hope this helps, Andy

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Re: Drive side main bearings

Postby Peter-Karl » Fri Dec 15, 2017 1:04 pm

Peter-Karl wrote:Hi all,
on my AJS 18s I have to re-press the main ball bearings,however, the small ball bearing has no tight fit, I think I'll fit in with Loctite. has one done something like that before ?What kind of sealant is the best? Loctite 648 could be the best but 648 is fixed within 5 minutes so I hardly have time to mount it.
Peter


Preview: Re: Drive side main bearings

Thank you for your replys

AJS is made 1957

there are the ball bearings that were already installed and they are still very ok,I had to remove it because a wrong washer between the bearings was installed.The bearing is not directly loose but I feel it went too well out.It had been previously installed with a sealant. I do not want the bearings in the housing turns so I will put it back with a sealant.I have experience with such things but in a AJS motor housing I haven't done something like that.
So the question was: did you ever do that? What a glue you took ?
Peter

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Re: Drive side main bearings

Postby cfaber » Fri Dec 15, 2017 4:44 pm

*shrugs* see my thread about about restoring a '54 where the PO decided to glue things together.

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Re: Drive side main bearings

Postby George Kaplan » Sat Dec 16, 2017 9:42 am

Hello Peter, there are various adhesives made for securing bearings in housings. The problem with using one on a motorcycle bottom end is that the case is usually made of aluminium and the bearing is made from steel. This means that you will get differential expansion between room temperature and at full engine temperature.

I am not saying that the sealant/adhesive wont work but I am just saying to be careful and do enough research before you finally decide. I have heard of people using adhesives in similar situations with good results and I have also heard of people using them with bad results. It may be down to the looseness of the fit or maybe the use of an activator? I am not sure but there must be lots of variables.

If it were me, if the bearing is only just a bit lose then maybe I would consider it. However if the bearing drops in easily at room temperature then maybe think of another solution.

There is a thread going on another forum at the moment with someone with a similar problem. He has opted for copper plating the outside of the bearing race to build it up a little bit to get the required fit so maybe that could be an option for you too?

John

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Re: Drive side main bearings

Postby Peter-Karl » Tue Dec 19, 2017 8:31 pm

Hi John,
your words are interesting, they seem to be right.It is also a time factor in the rapidly hardening sealant that leaves only a short time(5min) for assembly the bearings in the case.Cooper plating is not recommended because aluminum and copper should not be brought into direct contact.To move on I have to decide for something,because the rotating forces are not that strong I think I will install it with a non-full hardening adhesive like Black-sealant, it stays elastic and can be released.
Peter

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Re: Drive side main bearings

Postby George Kaplan » Tue Dec 19, 2017 9:08 pm

Peter-Karl wrote:Cooper plating is not recommended because aluminum and copper should not be brought into direct contact.
Peter


True, if the two metals are also in contact with a common electrolyte. Surely the presence of engine oil would prevent galvanic corrosion?

However I am no chemist so I am happy to be corrected?

John

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Re: Drive side main bearings

Postby Peter-Karl » Wed Dec 20, 2017 2:37 pm

George Kaplan wrote:
Peter-Karl wrote:Cooper plating is not recommended because aluminum and copper should not be brought into direct contact.
Peter


True, if the two metals are also in contact with a common electrolyte. Surely the presence of engine oil would prevent galvanic corrosion?

However I am no chemist so I am happy to be corrected?

John


You have right, usually the electrolyte is missing at this place except the motorcycle is used as a submarine :o I was by profession heating and plumbing so my dislike for copper / aluminum together.
,

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