Layshaft constant mesh gear

[Slymo]

Found another anomaly with the nice tidy cogs that I got for my A10 SR. Not only does the sleeve gear have a small bore than the usual (sorted with a machined bush ) but the corresponding layshaft cog has splines that run to the end of the dogs that won’t let it slide in over the circlip on the end of the layshaft. Is this a non swinging arm feature or another rogue part? Couple of hours later I’ve worked out that it is a Plunger part but that with the careful use of a tungsten carbide burr and a similarly equipped tool in the lathe I got it to fit perfectly. Nothing’s simple is it!

[Swarfcut]

Slymo   Plunger and S/A layshafts are identical as regards dimensions (splines, shaft diameter) but have a couple of differences.  S/A layshaft has a scroll at the blind bush end, plunger is plain.

  Circlip groove position is also different, circlip sits deeper into the layshaft pinion on Plunger shaft, the circlip locates at the tips of the dogs on the S/A shaft.

  Layshaft pinion dogs on Plunger are "square", later S/A are a  more rounded profile. The circlip position on the pinion is machined to match the appropriate layshaft.  Could be the parts you have are a mix from both boxes, and that's why the pinion won't match the layshaft.

  As a set, gears and their matching layshaft will fit either box casing on plain bush gearboxes.

 Swarfy.

[JulianS]

Photo show plunger fixed layshaft pinion on left and swinging arm one on the right. both 17 teeth.

[Slymo]

Yes thanks all. Much as I expected. I’ve modified the pinion to fit on the swinging arm layshaft and it’s dogs mesh perfectly with the neighbouring pinion so with any luck the box will work well. I’ve stoned and polished the mainshaft where it goes through the sleeve gear and bored the new bush in the sleeve gear so that it has around .0015 clearance. The new modified layshaft pinion is a much tighter fit on the layshaft and so I’m hoping that the general reduction in slop will result in a quieter box. I’ve also bought some Moreys in case all else fails.

[Slymo]

Huge improvement with third gear noise. It’s about 10% of what it was and not much louder that first and second. Easily explainable as straight cut gear whine. Slightly clunkier change into third with the rounder profile dogs on the modified layshaft pinion but only if you’re picky. Could be because I’ve tighten the clutch springs as there was slight slip at high speed acceleration but I am happy.