Tight crank bearing

Information relating to the Matchless G9 or AJS Model 20 500cc twin
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Duncan
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Re: Tight crank bearing

Post by Duncan »

It looks like you have an original brass cage factory fitted bearing there, it will be the rollers on the inner cage that will be giving you a fitting problem as I said eariler, I suggest you persevere in trying to persuade the rollers to engage, you will only be making work and expense for yourself otherwise. One option to convince yourself they will fit is to hold them in place with tape or an elastic band to see that they will engage, you will have to take it apart again to retrieve the items but it should give you the confidence to carry on as you will know that the race will fit.
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1608
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Re: Tight crank bearing

Post by 1608 »

I don't quite see the point in persevering in trying to put it back together as it is if, as first mentioned the bearing tolerances appear too tight. If you remove the whole bearing you will then satisfy yourself as to whether its worth replacing or not. If, as suggested it is an original bearing ( 50 or 60 yrs old ) then its worth checking it for wear. It really is a ha'porth of tar job in my opinion. If the engine has been taken apart so far then a thorough check and replacement of bits as necessary is the way to go. Then, when its back together you can forget any major internals needing further attention again.
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Duncan
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Re: Tight crank bearing

Post by Duncan »

I don't quite see the point in persevering in trying to put it back together as it is if, as first mentioned the bearing tolerances appear too tight.
Ah, but you are assuming that it is tight, if it is original there is no reason why it should be tight and it is most likely to be the rollers falling back in their cage that are preventing reassembly. At a touch under £70 per bearing I think it may be worth being sure that they need replacing, would you?
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ajscomboman
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Re: Tight crank bearing

Post by ajscomboman »

Not to mention the fact that he said it was running smoothly before disassembly.
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1608
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Re: Tight crank bearing

Post by 1608 »

My mistake, I didn't realise that it was just tight putting it together. Yes, its a classic case of the rollers being stubborn.
theEagle
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Re: Tight crank bearing

Post by theEagle »

Thanks for all the replies and comments!

1608: I did try a bit with the chisel even if that is a bit out of my comfort zone. I removed most of it but after a while started to realize that i do not think I will be able to remove enough to just heat/drop it out. I am pretty convinced that I would still need to drive it out and I am reluctant (at this stage) to drill the holes needed to drive it out. I did try to heat the case (not very much) with a gasburner and banged it on wood, but it did not give a mm).
Also I am not sure that the puller I can find for a decent price can be fitted in the narrow gap if I want to pull off the inner bearing.
There are no visible c3 mark and the search on the number did not give much..

ajsph: Thanks for the tip! It really seem like an idea to test, however I am short on resources to get that piece of Al manufactured.. but i will keep it in mind. Thanks.

Duncan: I am doubtful..BUT I am glad you are pushing me and I will give it another try! I am doubtful as the outer bearings have a good chamfer and should centre the roller.. AND it works on the drive side... ..BT again, as you say, if this approach works it is the best/easiest! I will try with tape, no problem to try it and take apart again (unless it sticks.). Thanks!

1608: Thanks for the thoughts. And in one way I do completely agree with you. However,
firstly: I am not a very skilled mechanic and have a limited set of tools.
secondly: I usually do projects in 2 steps, first a quick and dirty to show it works (mainly for myself) , Then a second step where i go back and correct things discovered properly.
thirdly: In this case I need to balance the risk of damaging something in the process, my limited time available, my first level goal to show that it can run at all (!!), cost..
So, I know that the "right" thing to do would be to pull off/out teh bearing and race and check if tehy need change etc.. BUT there are many steps in that process that worries me.

As the crank turned freely when i got the engine, in boxes (crank case and shaft assembled). I assume that it would NOT damage the engine to run for a few hours assembled with that tight fit ? This assembly that i do now is intended for that first tests to see if I CAN get the engine to run at all without to large cost.

Duncan 2nd: I completely agree that it should be properly tested! (and yes bearings are bit expensive..)

Thanks you for all the comments and please continue to comment.
My current plan is now to:
1. See if it helps to keep rollers in place with tape! (easy test :)
2. Try to fit it together as is, tighten the web centre, mount cams followers etc, add gasket sealant, heating the case and then try to gently drive the timing case (and outer bearing race) in place.
3. if that does not work OR as a future fix, split the case and start to drive out the outer race, potentially followed by the bearing.

Thoughts on this ?
Anders
theEagle
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Re: Tight crank bearing

Post by theEagle »

1608: On your last comment.
BUT I had to laboriously drive the case apart first time..should that not indicate that there was a constant pressure on the rollers, and not just that they need to be kept "in" when assembling?
Anders
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Re: Tight crank bearing

Post by alanengineer »

i trust you put the outer race in dead square. Lets have a photo of what it looks like now
ajsph
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Re: Tight crank bearing

Post by ajsph »

the plate behind the bearing should not be there
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theEagle
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Re: Tight crank bearing

Post by theEagle »

IMG_5061.JPG
This is as far as I get down with rubber bands on teh rollers
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