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Mk3 Swinging Arm Cotter Pin Fitment

Submitted by andrew_mackenzie on Sun, 01/09/2019
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Commando

Hi,

I bought a brand new Mk3 gearbox cradle off eBay in 2017 with an A–N Southhampton label and powder coating masking foil still on.  Now that I finally started preparing the cradle for fitment, I found that the two swinging arm spindle cotter pins do not go through their tubes far enough to allow the nuts and washers to fit correctly.  The new spindle and pins fit perfectly in the original damaged cradle (top gearbox bolt hole crudely slotted by previous owner for belt drive conversion).  The thread protrusion in the new cradle is 7mm and in the old cradle 12mm – quite a difference, with no obvious visual or dimensional explanation.

The cotter pin tubes are clean, free of powder coat, not burred and the same diameter as original.  The pins and spindle are also the same dimensions as the originals.  All I can think is that the two tubes were welded in fractionally too close to the centre of the cross tube?

Has anyone encountered this issue before?

Regards,

Andy

Submitted by richard_payne on Sun, 01/09/2019

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I've always had to file the taper on the cotters when fitting Mk3 spindles, as I have with bicycle cranks using any pins bought in the last forty years - Old stock pins seemed to enter properly but somewhere along the line, all the pins on the market seem to have acquired too acute an angle.

That they fit your old cradle may just be due to wear either in the main cross-tube or the pin locating tubes.

Submitted by john_holmes on Sun, 01/09/2019

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There are various tapers on cotter pins around, BSA and Triumph ones do not mix well even before you get to fitting them to worn parts. I have bought them with no taper at all and filed one to suit when I had the opposite problem to you  i e they all went in too far. As Richard suggests take a file to the taper and adjust until they go in and give you the 12mm.

Submitted by andrew_mackenzie on Mon, 02/09/2019

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Thanks for the comments, Gents.

The fit of the cotters pins in both old and new cradles is identical, as is the spindle fit in the cross-tube, and I have an original pin that fits just the same as the new ones, so not a new pin issue.

 However, cotter pins are cheap(ish), so will get reshaped, rather than reaming the tubes.

Curiously, the swinging arm bushes I removed were the earlier longer ones, even though welch washers were fitted, and the spindle had a groove machined midway along each bearing surface with a hole drilled through to the centre of the spindle.  That would have been a good idea if there was a grease nipple somewhere to force grease through, but there wasn't.  There was residual grease present, not EP140.  So a non-standard set-up that was strangely pointless.

I intend to fit standard short Mk3 bushes, but with the early end plates, o-rings and through bolt arrangement, with EP140 fed through the RH end plate grease nipple.  I used that arrangement on the MAk3 I had in the early 80's, which seemed to work well without leakage.

Cheers,

Andy

 


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