The BSA A7-A10 Forum

Technical => A7 & A10 Engine => Topic started by: Alex kettle on 03.11. 2016 20:16

Title: Crank and bearing help needed
Post by: Alex kettle on 03.11. 2016 20:16
Ok so I've stripped the engine all down and cleaned everything like new and ordered lots of new parts.  I am thinking something is suspicious with the crank and the main bearing. When stripping it down it struck me as an unusual set up but as the a10 engine is a new one on me I am non the wiser. I hope you all can put me right. If you look at the photos below it look to me like the main bearing has been ground down on the inner race and then a 2mm washer made to bring it back up to correct thickness. The washer is much larger diameter than the inner race of the new bearing from srm. I can only come to the conclusion this has been done as there is a step in the crank where the new bearing race would sit and the bigger washer style of the old bearing sits over this further out on the crank. I hope this makes sense. So I suppose what I am asking is should there be a step in the crank and has the original bearing (left on photo) been messed about with?
 As they say a picture tells a thousand words. Let me know your thoughts. Many thanks for help in advance
Alex
Title: Re: Crank and bearing help needed
Post by: KiwiGF on 04.11. 2016 02:17
Is this just the drive side bearing we are looking at ?

Is the old bearing a roller or Ball bearing type?

im also thinking the washer may be to get the end float correct, instead of using shims which sometimes disintegrate.
Title: Re: Crank and bearing help needed
Post by: Alex kettle on 04.11. 2016 06:55
Hi kiwi. Yes this is drive side and both are a roller bearing .

I think the large washer which makes part of the old bearing was created to take care of the wear on the crank where the new bearing face would sit.
Title: Re: Crank and bearing help needed
Post by: KiwiGF on 04.11. 2016 08:33
Hi postman, I think you just need to follow the standard build process and put it together and measure the end float then either fit the correct shims, or get a single thick shim made up.

It's a bugger to have to fit the new roller bearing then remove it without damaging it, a way around that is to test build by fitting an old bearing with the i.d. Ground out so it's a loose fit, emery cloth and a lathe can do the grinding out as you only need to take off a thou, and calculate the correct shim thickness using the old bearing. That way you should only have to the fitting of the new bearing once, your old bearing if modified cannot be used for this obviously.

Others will chime in I'm sure but I think it's not uncommon to have to use a shim of 040, from what you've said yours may come in under this, which would mean your crank is not unusually worn in the bearing area.....I think....

Title: Re: Crank and bearing help needed
Post by: beezermacc on 04.11. 2016 10:32
From looking at your picture I would say the old bearing is of a type which includes the washer as part of the bearing. It looks like the washer, when fitted to the bearing doesn't actually make the bearing any thicker, i.e the edge of the outer track is flush with face of the washer. I've not come across this type of bearing in this application before. However, as Kiwi says, I'd just follow the standard fitting procedure, using shims trapped between the inner track and the flywheel, to get the correct endfloat.
Title: Re: Crank and bearing help needed
Post by: mugwump on 04.11. 2016 10:56
I agree with Poshman. There also appears top be a witness mark on the c/shaft face where the outer shell of the bearing has made contact with it.
Title: Re: Crank and bearing help needed
Post by: Alex kettle on 04.11. 2016 18:27
Beezermacc you are right it in no thicker than the new bearing.  But I fear the face of inner part of the new bearing (as it's not got the surface area of the old one) end up sitting against the rough crank face I have?
This is my concern mugwump as the new bearing will sit where the rough face / step is on the crank face.  I have access to phozi bronze. Is it worth my while testing endfloat and making a phozi bronze washer to go against the crank face and the new bearing? I want to get this right. Thanks again for all your responses.
Title: Re: Crank and bearing help needed
Post by: dave55 on 04.11. 2016 18:40
Im only a novice but would it be possible to get the crank face repaired and reground then use a thicker shim ?  :!
Title: Re: Crank and bearing help needed
Post by: KiwiGF on 04.11. 2016 22:29
Hi poshman, one thing to consider is the inner race of the roller bearing is clamped up hard against the crank when the Cush drive nut is done up, theoretically there is no possibility of shims placed between the crank and bearing spinning relatively to each other and hence wearing, note this applies to the later bikes like yours..... I'm not sure 100% the race is clamped this way on earlier models.

The use of incorrect Cush drive parts eg the sleeved spline part can result in the inner race not being clamped properly, and hence problems with shim, and I suppose crank face, wear, albeit I've not seen that clamping problem myself.
Title: Re: Crank and bearing help needed
Post by: mugwump on 05.11. 2016 14:51
Poshman1, I believe bronze may be a bit too soft for that application. Has anyone got a pic of a crank to enable a comparison re the shoulder that appears to have been removed or worn away.
Title: Re: Crank and bearing help needed
Post by: RichardL on 05.11. 2016 16:11
You could have it welded and machined down, but I think that is too extreme for the situation. I believe the depression just changes the size of the shim stack required. Once compressed behind an inner race that doesn't move, the surface they're sitting on shouldn't matter, bearing in mind that shims sitting on a perfect surface shred when the race moves.

Richard L.
Title: Re: Crank and bearing help needed
Post by: KiwiGF on 05.11. 2016 20:00
I would avoid doing any welding on a crank at all cost, and as per other posts the situation does not warrant an extreme measure like that, it's bound to cause it to bend! (And even a very small amount of bend would be bad).

I've only got a small journal crank I could photo so no point in me digging that out, a 1960 bike will have a large journal crank.
Title: Re: Crank and bearing help needed
Post by: RichardL on 05.11. 2016 20:26
kiwigf,

I'm sure you noted that I was not.recommending welding, but for a different reason than yours. My local engine machine shop has journal welding equipment and they have assured me that a weld buildup would be possible for renewing my crank when the time comes. Of course this is not the same as the web, but I can't see the difference.

Richard L.