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Kickstart Shaft Shimming

Submitted by andrew_mackenzie on Sat, 19/02/2022
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I spent some time getting the Mk3 layshaft endfloat (with roller bearing) to just over 0,020”, which was easily repeatable while the kickstart shaft spring was not fitted.  With spring fitted, there is obviously more resistance to shaft movement, though it still does move, but it appears that the shaft position under tension could leave the layshaft without any float.  I have also noted that the kickstart pawl is noticeably less deeply engaged with its stop - see the original contact mark in the photo.

Consequently, I think some of the 0,050” shims will have to come out to increase the float and pawl depth.  I have seen comments (John H I think) that the gearbox actually operates fine without shims, so maybe trying for a set endfloat is not worth the effort?

Andy

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Submitted by robert_tuck on Sat, 19/02/2022

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You could try a shim between the layshaft 4th and the roller bearing flange , seems to me that this would replicate the orriginal positions before the  weak ball race was  uprated by the roller bearing and the excess end float  materialised.

Submitted by john_holmes on Sun, 20/02/2022

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I think I put shims in but its a few decades ago, but I definately pulled the bush out of the kickstart shaft and replaced it with a needle roller which reduces the wobble in the shaft as the running clearance is much reduced. Not a straight swop as the layshaft needs grinding to suit the ID of the needle roller. 

Submitted by andrew_mackenzie on Sun, 20/02/2022

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Thanks for the contents.

When I first assembled the layshaft with the fourth gear, it was in perfect alignment with the sleeve gear, but I had not checked first gear alignment too closely due to mainshaft freedom of movement.  Just checked by measuring  mainshaft protrusion from the sleeve gear with the inner cover fitted, then setting it to that with the inner cover removed.  The two first gears are pretty neatly aligned, indicating that the roller bearing is not causing the 0,070” endfloat I had measured before shimming the kickstart shaft.  I will just remove perhaps 0,020” from the shims and leave it at that.  If endfloat had not been mentioned on the forum I would never have known about it and likely never had an issue because of it!  Over-thinking perhaps! 

Andy

Submitted by robert_tuck on Sun, 20/02/2022

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I had a similar experience after fitting  the layshaft roller bearing.  About 60 thou end float on the KS after all assembled, Fitted a 40 thou shim  between bearing and 4th gear . All seemed well. Then advised not to do this ,so fitted about 40 thou of  Iso shims (with bore increased) at KS end . This locked it all up. Took out 20 thou , now have a couple of thou end float.  I took the hint and left it alone. Works well.

Submitted by ashley_cutler1 on Mon, 21/02/2022

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If you really feel a need to shim anywhere along the layshaft, I would not go under 20 thou. Less than this and you could remove one or more of the tolerances along the shaft. There are lot of parts all in the line, all with their own tolerance, and some which engage with other parts in the line.

The MK3 gearbox assembly drawing shows shims with a part number. I've never seen them fitted, or a drawing for the part number of the shim. The drawing gives a figure to shim to.

I have heard of several shimmed boxes failing at low mileages, but these were shimmed to stupid low figures. Unshimmed, will cover large mileages, more than what most owners will cover in 10 years. 

 


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