Crankshaft bearing woes

Information relating to the Matchless G3 or AJS Model 16 350cc Heavyweight
sno335
Member
Posts: 28
Joined: Thu Jun 11, 2020 12:14 am
Location: Northamptonshire UK
Location: Long Buckby

Crankshaft bearing woes

Post by sno335 »

Hi,I recently posted this to the wrong section so apologies if I 'm repeating myself.
I just fitted new drive side bearings into my 1954 G3 case.
When I attempted to fit the axle into the bearing it only goes in about a 1/16th " then jams solid and needs a rubber hammer to remove it.
I measured the axle and it is 25.4 mm in new money.
I bought the RHP bearings from AMC Spares.
The manual says it should be a push fit not a press fit,so endfloat can be checked?
AMC Spares say it should be a tight fit I'm confused.Anyone had a similar experience.The old bearings slide on without being sloppy.
Any advice welcome.
Andy51
Member
Posts: 742
Joined: Thu Mar 31, 2005 1:00 am
Location: BERKS UK

Re: Crankshaft bearing woes

Post by Andy51 »

I have a '54 G80 so identical cases. The shaft should, as the manual says, be a push fit; the shock absorber nut holds everything in place and stops the inner race turning on the shaft. End float is then adjusted by moving the timing side bush in or out to give around 20 thou (check manual) float. if the shaft is too tight in the ball races it could give rise to false endfloat readings as the s/a nut might not pull the shaft through the bearings properly. Mine was a light push fit, but I did have problems with the outer race fit using some bearings from Steve Surbey. Heated up the case, the bearings dropped in nicely. As the crankcase cooled and contracted, it locked the bearings up. Steve immediately sent me some branded (RHP?, can't remember) bearings and all was well. Do your bearings spin freely? It may be possible for the case contraction to squeeze the inners? Hope this helps, Andy
sno335
Member
Posts: 28
Joined: Thu Jun 11, 2020 12:14 am
Location: Northamptonshire UK
Location: Long Buckby

Re: Crankshaft bearing woes

Post by sno335 »

Thanks for the input.I heated the case and the bearings came out easily.I then tried the bearings on the axle again.I gently tapped one on a very small amount but then needed a bearing puller to get it off.I measured the inside diameter as best as I could with my basic vernier and it would appear to be 25.4 mm,the same as the axle as measured with a Moore and Wright mic.(which I rechecked for zero just in case.
So there is no appreciable clearance.
It would seem although the bearings are a reputable make, their quality control is not all that good.
My next course of action is to try to seal the ball races with sticky back plastic or silicone to keep debris out and use a brake cylinder hone to remove some metal,to allow them to fit.
Having paid £60 for the bearings I can't afford to just try another supplier who may just send a similar it anyway!
Mick D
Posts: 2886
Joined: Mon Mar 24, 2014 5:44 pm
Location: Aberdeenshire

Re: Crankshaft bearing woes

Post by Mick D »

Hi

I would suggest that there's much more chance of there being imperceptible damage to the drive side axle which is causing the interference fit - try some very fine wet and dry paper on the bearing surface, particularly the outboard end.

I'd also consider warming the bearings with a hot air gun just before installing the crank shaft.

When everything is bolted up I don't think there is any end float on the crank shaft, just a minimum 0.012" clearance at the timing side bush, (which can be set by temporarily installing shimming washers).

Strange that the Workshop Manual indicates one of the drive side bearings to be a C3, (above mean clearance), but not the other :? :?

Regards Mick
sno335
Member
Posts: 28
Joined: Thu Jun 11, 2020 12:14 am
Location: Northamptonshire UK
Location: Long Buckby

Re: Crankshaft bearing woes

Post by sno335 »

Thanks Mick, you could be right and that's probably the simplest solution.I checked with the mic all along the journal as well as radially ,visually as well and it seemed undamaged.According to the spec it's smack bang in the middle of the tolerance.I did gently rub it down before the last attempt but there was no improvement.
Yes I realise there shouldn't actually be endfloat when it's assembled,but it would be easier to check for clearance at the timing bush if it slides.
Otherwise it's hard to check.Although I did consider using a depth gauge through the little hole in the timing side case by the cams before and after assembly.
Well I think I'll leave it a couple of days then have another go.
Thanks for the input ,much appreciated
Regards John
56G80S
Member
Posts: 3354
Joined: Wed Oct 12, 2005 10:45 pm
Location: N YORKS UK

Re: Crankshaft bearing woes

Post by 56G80S »

Have you been back to Steve at AMC Classic Spares (assume that's who you meant). My experience is he is not only knowledgeable but obliging.

Johnny B
sno335
Member
Posts: 28
Joined: Thu Jun 11, 2020 12:14 am
Location: Northamptonshire UK
Location: Long Buckby

Re: Crankshaft bearing woes

Post by sno335 »

Yes I phoned him and explained how hard the bearings were to fit was and the internal size as I had measured it.He insisted the bearing was good quality and therefore accurate.I said that the bearing should be a slide fit but he insisted that it should be a tight fit on the axle or it would wear it away.This would seem contrary to the workshop manual as the sprocket ,cam and spring holds everything tight in tension so it can't move.
It also quotes checking the endfloat without the shock absorber assembly fitted.This would indicate that the axle should be able to slide.The old bearings do and there's no sign of wear inside them or on the shaft.So I'm none the wiser but thanks for the tip
Regards John
Andy51
Member
Posts: 742
Joined: Thu Mar 31, 2005 1:00 am
Location: BERKS UK

Re: Crankshaft bearing woes

Post by Andy51 »

This month's Classic Bike Guide shows someone using emery cloth strip to ease a tight mainshaft on a Norton ES2. Given the hardness of the shaft it would take some time to remove any significant amount of metal but could be the way ahead. Andy
sno335
Member
Posts: 28
Joined: Thu Jun 11, 2020 12:14 am
Location: Northamptonshire UK
Location: Long Buckby

Re: Crankshaft bearing woes

Post by sno335 »

Thanks Andy,
I'm probably going to do that,I don't think I'll need to take much off probably a thou or 2 to make a difference.I'll definitely read the article.It's possible the imperial size bearings made now are not the same size as the originals .
Regards John
Steven S
Member
Posts: 52
Joined: Mon Jan 01, 1990 12:00 am
Location: BEDFORDSHIRE UK

Re: Crankshaft bearing woes

Post by Steven S »

I don't think it's correct to blame the bearings. A modern bearing from a premium manufacturer like RHP will be made to far greater precision than achievable by Skefko, Hoffman etc back in the 1950s. Similarly a company with a global reputation making millions of bearings annually is very unlikely to have any issues with quality control. Any quality 017191 bearing should measure 1” dead on the ID. I will continue to stock RHP bearings and sell them with confidence, especially as they are one of the few still made in England.

It's more logical to look at the drive side axle itself. In my opinion, bearings have always been the fixed reference point with a definitive measurement, so it's up to the manufacturer to make their part to suit. Confusingly the factory workshop manual specifies a shaft measurement of 1.0002” high and 0.9997” low. Obviously the differential is tiny but given the 1.000” ID on these bearings, an axle on high limit will prove problematic. It also means the area for the bearings on the shaft must be flawless, as any little imperfection will prevent proper fitment.

Even the lower limit is higher than I would expect. In real life, I've found most original shaft measurements to be less than the specified limits, which would provide the requisite clearance on the bearing. Are you sure your shaft is original? If there's very little wear on the splines, then I'd expect it to have been changed at some point in the engine's life. I believe there was a batch of reproduction axles several years ago that were .001” oversize.

I didn't mean that the bearings should be tight on the axle. The factory workshop manual states that the bearings should be a ‘snug push fit' on the shaft but I would go a bit further and say that you're looking for a light interference fit. What I was trying to point out is if the bearings are an easy fit, you run the risk of having the crank rotate independently of the bearings.
I agree with Mick D and suggest that you use some fine wet & dry on the shaft.

Steve
Locked