Drive side main bearings.

Information relating to the Matchless G3 or AJS Model 16 350cc Heavyweight
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Re: Drive side main bearings.

Postby Expat » Thu Apr 13, 2017 11:36 am

The outer bearing was certainly fully located in the crankcase... that was what stopped the crankcase from going any further.

John[/quote]

John, Thanks for the update.

Regards, Steve
Keep shiny side up.

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Re: Drive side main bearings.

Postby Mick D » Thu Apr 13, 2017 2:53 pm

Hi John

I hope your assumptions are correct and you get plenty of service out of the bike but I would still recommend installation with a press. A press ensures the bearing is correctly seated, it doesn't rely on the free movement of the bearing in the case. It eliminates the doubt that the bearing could move in operation. It also eliminates the chance of the bearing 'cocking' on installation.

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Re: Drive side main bearings.

Postby Pharisee » Thu Apr 13, 2017 3:38 pm

Mick D wrote:Hi John

I hope your assumptions are correct and you get plenty of service out of the bike but I would still recommend installation with a press. A press ensures the bearing is correctly seated, it doesn't rely on the free movement of the bearing in the case. It eliminates the doubt that the bearing could move in operation. It also eliminates the chance of the bearing 'cocking' on installation.

Regards Mick


I appreciate your comments, Mick but believe me... the bearings are fully seated in the case. Installing the bearings onto the crankshaft first ensured that there was no possibility of the the bearings 'cocking'.

Think about it... The 'approved' method of installation in the manual shows the bearings and spacers on a shouldered mandrel and using that to drive (press?) them into the crankcase. The mandrel is removed and the crankshaft pushed in afterwards. How is that any different to what I've done...? I put the two bearings and spacers onto a shouldered mandrel (in this case, the drive side axle) and installed them into the crankcase. Only thing is, I don't have to remove the mandrel (and hope the spacers don't move as there is nothing to locate them). Warming the crankcase up just means that the bearings slide into position easily and there's a lot less chance of damaging the bearings or the bearing register than there would have beeen if I'd banged them in cold. When the crankcase cooled down, the bearings were held firmly in place with no more chance of them 'moving in operation' than there would be if I'd installed them cold... and with less chance of damaging the crankcase. :)

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Re: Drive side main bearings.

Postby Mick D » Thu Apr 13, 2017 3:54 pm

Hi John

I will agree to differ - I prefer the knowledge that the bearing has been fully pressed into the warmed case rather than rely on gravity / hand pressure :)

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Re: Drive side main bearings.

Postby Pharisee » Thu Apr 13, 2017 5:46 pm

Mick D wrote:Hi John

I will agree to differ

Regards Mick



Agreed... :D

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Re: Drive side main bearings.

Postby bodgert » Fri Apr 14, 2017 10:00 am

By fitting bearings on shaft first when fitting into case you will be pressing bearings on inner race which is not recomended

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Re: Drive side main bearings.

Postby BobbyG » Fri Apr 14, 2017 2:44 pm

Enjoyed reading 'Matchless Stuff'. Looking forward to the next installment(s)!
Robert Gallagher

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Re: Drive side main bearings.

Postby Pharisee » Sun Apr 16, 2017 9:03 pm

bodgert wrote:By fitting bearings on shaft first when fitting into case you will be pressing bearings on inner race which is not recomended


If there was any 'pressing' involved you may well be right but the heated case dropped over the bearings without the need for any pressing, bashing or any other form of persuasion.

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Re: Drive side main bearings.

Postby Iron Head » Thu Dec 31, 2020 3:54 pm

Although this is an old post, having just fitted my drive side main bearings following John's instructions, I just wanted to respond by giving a massive thumbs up to his excellent method which, from what I can see, exerts zero stresses on any part of the rolling element system.

Some observations from me and from information gained from an excellent bearing company whom I work very closely with and who kindly gave me my SKF RLS8's in return for three bottles of nice wine!

- A temperature differential of 80-90 degrees C between components to be fitted should (in theory) be all that is required.

- 200 degrees C is fine for the crankcase but rolling element bearings should not be heated above 120 degrees C.

- Ambient temperatures are fine for the crankshaft for fitting (degreased) heated bearings (120 degrees C) onto. Similarly ambient temperatures are fine for the crank/bearing assy to have the 200 degrees C crankcase half placed over. No need for crank in freezer as I had supposed (happy wife).

- I was quick fitting the case but it would appear you have plenty of time, case 'rocked' on the outer race so was categorically fitted home. Crankshaft on drive side end was still too hot to touch from heat transfer even after 15 minutes. Also, early on, the inner race was moving on the crankshaft not the bearings rolling due to expansion?!

- Whilst the crank might conceivably be able to move at hot working temperatures(?) on the inner races I am unsure about the theory that crank end float can somehow be taken up by tightening the drive sprocket nut and thereby somehow sliding the crank through the inner races or by the outer races moving in the drive side crankcase housing. The main bearing inner races are hard up against the crank driveshaft step by the flywheel with the spacers tightly squeezed between them, nowhere to move there. Similarly the main bearing outer races are hard home in the housing - nothing to take up there from what I can see.

- From the illustrations I have, and from how my case came off the crank, with one bearing on the crank and one in the case, one other method to consider, and how AMC may have done it, was to fit one bearing to the crank and one to the tighter inner step on the crankcase then heating the case to about 120 degrees C to fit crank to outer bearing inner race and inner bearing outer to case which should be easy going. John's method however seems much simpler.

Just my thoughts of course.


Happy New Year to all and good riddance to 2020


Iron Head

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Re: Drive side main bearings.

Postby Pharisee » Fri Jan 01, 2021 5:06 pm

I'm glad it worked out OK for you. I have an aversion to bashing things with a hammer, unless they are nails, and will always try to avoid it if I can. However, I fully appreciate that it is sometimes necessary.
I note your comment regarding heating bearings to no more than 120° C and will use that as a maximum in any future assembly.
Happy New Year to you all... God, it just has to be better than the one we've all just endured.
John

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