Roller Layshaft Bearing Failure?

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Dan1950

Dan1950

1974 MK II Roadster
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It has been just over 3000 miles since I went completely through my gearbox with all new seals, springs, sleeve gear and 4th gear layshaft gear, new inner and outer cover, bushings and bearings including the roller layshaft bearing from AN.

All has seemed fine until recently when I noticed the kick lever jumping back when accelerating sharply in low gear.

I don't see how the roller bearing could have failed in such a short time and even if it did, would it exhibit the same symptoms as the failing ball bearings?

Going out to have a look as soon as I finish my breakfast bagel.
 
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The layshaft is supported by the roller bearing on one end and in the internal bush in the kickstart shaft, this is further supported by a bush in the inner cover. So the suspects are these two bushes as there are 2 clearances involved. The other possibility is a worn bush inside layshaft first gear with the internal teeth for the kickstart pawl, if this can lean over then it can rub the kickstart shaft which fits in with the low gear observation.
 
kommando said:
The layshaft is supported by the roller bearing on one end and in the internal bush in the kickstart shaft, this is further supported by a bush in the inner cover. So the suspects are these two bushes as there are 2 clearances involved. The other possibility is a worn bush inside layshaft first gear with the internal teeth for the kickstart pawl, if this can lean over then it can rub the kickstart shaft which fits in with the low gear observation.
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New inner cover from AN so that bush is not suspect. Also I believe I replaced the bush in the low gear layshaft gear as I used the "kit" from AN that has new seals, springs and bushes. The bush inside the kickstart shaft might be suspect though.

From WOT off idle in 1st gear, the kicker will only go parallel to the ground, no further. Less than 90 degrees.
 
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L.A.B. said:
How much kickstart shaft end float?
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I don't remember exactly but it's near the minimum spec.

That is something I am suspicious about though. I didn't seem to have this problem until I replaced to outer cover to get the updated seals due to leaking around the kicker shaft on the original. Perhaps this put things in closer alignment aggravating an existing issue?
 
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In addition to the sleeve gear and 4th gear layshaft gear, inner and outer covers, this is the "kit" I used to rebuild my gearbox.

Roller Layshaft Bearing Failure?
 
If the new outer cover has the holes out of sync with the old inner cover then it could be pulling on the kickstart shaft enough to get it to bind on one of the other bushes. BSA had this issue with inner covers and crankcases, they solved it by machining them together and stamping a matching number on both, so they could be reunited in the works if they got separated. So in this case new bushes will make the issue worse until the holes are aligned.
 
kommando said:
If the new outer cover has the holes out of sync with the old inner cover then it could be pulling on the kickstart shaft enough to get it to bind on one of the other bushes. BSA had this issue with inner covers and crankcases, they solved it by machining them together and stamping a matching number on both, so they could be reunited in the works if they got separated. So in this case new bushes will make the issue worse until the holes are aligned.
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That's kind of what I am thinking. At least I don't think it is the layshaft bearing about to dump me onto the ground with a locked up gearbox .
 
Update:

It now seems to have cured itself somewhat.

I think I had a stack up of perhaps some tight tolerances, oppressively high temperatures (ambient temperatures in the 90s) aggravating the tight tolerances and perhaps a kickstart return spring that need a bit more oomph. After doing some maintenance and checking things over today I took the bike for a shakedown ride. No kickstart movement on somewhat hard acceleration, but if I would blip the throttle from a slow roll and get the bike to jump, the kickstart would bounce backwards through it's free movement. From the resting position, it has about 30° or more of movement before it catches the ratchet teeth. After that I can ratchet it up to the top for full engagement.
 
My reservation with the roller bearing is the end float on the assembly has to be controlled with shims, and I wonder if this could be a factor?
 
B+Bogus said:
My reservation with the roller bearing is the end float on the assembly has to be controlled with shims, and I wonder if this could be a factor?
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This is one reason why I went with Mick Hemmings guidance to use the phenolic cage ball bearing for layshaft as he discusses in his gearbox rebuilding dvd. He mentions he has seen roller bearings leading to snapped LS due to less ability to flex when loading compared to ball bearing. Done hundreds with phenolic with no reports of problems.
 
Tornado said:
This is one reason why I went with Mick Hemmings guidance to use the phenolic cage ball bearing for layshaft as he discusses in his gearbox rebuilding dvd. He mentions he has seen roller bearings leading to snapped LS due to less ability to flex when loading compared to ball bearing. Done hundreds with phenolic with no reports of problems.
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I also use the Hemmings recommended 6203TB in all my rebuilds. It retains the positive location property of the original design as well as allowing the flex as you describe.

If someone came up with a third bearing immediately behind the clutch similar to the now unobtanium Maney outrigger, but incorporated into the primary case, I suspect it would sell.
 
B+Bogus said:
I also use the Hemmings recommended 6203TB in all my rebuilds. It retains the positive location property of the original design as well as allowing the flex as you describe.

If someone came up with a third bearing immediately behind the clutch similar to the now unobtanium Maney outrigger, but incorporated into the primary case, I suspect it would sell.
Click to expand...

Is there a good source for the Hemming’s recommended 6203TB?
 
SEd27 said:
Is there a good source for the Hemming’s recommended 6203TB?
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Search:
6203-TB-P6-C3 FAG or 6203-TB-P63 FAG.

www.123bearing.co.uk

Deep Groove Ball Bearing 6203-TB-P63-FAG 17x40x12 mm

<p>The Deep Groove Ball Bearing, known as 6203-TB-P63-FAG FAG, has an inner diameter of 17 mm, an outer diameter of 40 mm and a thickness of 12 mm.</p>
www.123bearing.co.uk www.123bearing.co.uk
endevoronline.com

bearing 6203-tb-p63 fag ball bearing fag 6203t Condition New

original 6203-tb-p63 fag ball bearing fag 6203tb-p63
endevoronline.com endevoronline.com
 
L.A.B. said:
Search:
6203-TB-P6-C3 FAG or 6203-TB-P63 FAG.

www.123bearing.co.uk

Deep Groove Ball Bearing 6203-TB-P63-FAG 17x40x12 mm

<p>The Deep Groove Ball Bearing, known as 6203-TB-P63-FAG FAG, has an inner diameter of 17 mm, an outer diameter of 40 mm and a thickness of 12 mm.</p>
www.123bearing.co.uk www.123bearing.co.uk
endevoronline.com

bearing 6203-tb-p63 fag ball bearing fag 6203t Condition New

original 6203-tb-p63 fag ball bearing fag 6203tb-p63
endevoronline.com endevoronline.com
Click to expand...
Thank you LAB. Seems to be a bit harder to find in Canada for a reasonable price.
 
I got my bearing with the gearbox rebuild kit direct from Mick. Has anyone taken up his business since his passing?
 
Tornado said:
I got my bearing with the gearbox rebuild kit direct from Mick. Has anyone taken up his business since his passing?
Click to expand...
most of the parts were sold to Andover Norton.They are only showing a roller bearing as the standard replacement.
 
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Over 18K miles on the the roller and other components installed at the same time, no issues as yet. I don't shim either, unless you can work out the tolerance build up along the layshaft then any shimming is guesswork.
 
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