Gearbox detail changes?

I managed to get a nearly new gear set complete with both shafts, shifter forks and the shifter fork shaft form Ebay for a very reasonable price to replace the somewhat pitted gears in my 850 Mk IIa.

Now I'm reassembling my gearbox, and I find that the new layshaft is an interference fit in the layshaft bearing, while the old shaft is a nice sliding fit.
OK, no problem, so just use the old layshaft with the new gears.

Next problem is that the new mainsheet is a very tight fit in the RH bearing. Loved this by easing off the shaft until I achieved a nice sliding fit.

Then when doing my test assembly, I find that the selector fork shaft is sitting too low relative to the inner cover. I removed it and checked it for bends, nothing visible, tried the old shaft, same problem. In order to fit the inner cover I have to move the shaft up by about 1/2 it's diameter.

This new box was probably from a MkIII, but I don't understand these small differences - there's no mention of any of this in any of the rebuild guides I've read.

Any ideas or comments?

Thanks,
Steve.

SteveBorland said:

Now I'm reassembling my gearbox, and I find that the new layshaft is an interference fit in the layshaft bearing, while the old shaft is a nice sliding fit.
OK, no problem, so just use the old layshaft with the new gears.

Click to expand...

Or ease the new shaft down a little, although the fit of the shaft in the bearing isn't critical.

SteveBorland said:

This new box was probably from a MkIII, but I don't understand these small differences - there's no mention of any of this in any of the rebuild guides I've read.

Click to expand...

Edit: If it's just the gearbox internals then there's basically no dimensional difference between the Mk2a and the Mk3 shafts and gears as most parts are identical.

I did the mainsheet this way, but the layshaft was a bit too much, which is why i chose the old shaft.
I do wonder about the selector fork shaft though. Perhaps try not screwing it all the way in, see if that helps?

/Steve.

SteveBorland said:

I did the mainsheet this way, but the layshaft was a bit too much, which is why i chose the old shaft.

Click to expand...

Mainsheet? Do you mean mainshaft or sleeve gear?

SteveBorland said:

I do wonder about the selector fork shaft though. Perhaps try not screwing it all the way in, see if that helps?

Click to expand...

I don't know what the problem is there, but I don't think not screwing the selector spindle in fully is the answer, as the "new" parts should be the exactly same as the "old".

Try using the old shifter forks.

Autocorrection catches me again - this being a motorbike site rather than a sailing site, it should be reasonably obvious that mainsheet was intended rather than mainsheet

I'm being a bit dense here, bit I don't quite see what influence using the old selector forks would have on the position of the selector shaft ?
I think I will just do a dry assembly of everything and see if the bugger shifts ok.

/Steve.

I'm being a bit dense here, bit I don't quite see what influence using the old selector forks would have on the position of the selector shaft ?

Click to expand...

Well the shaft goes through them, if they change position then so does the shaft. You have changed a lot of parts, either you have miss assembled them or a part is different. You need to find the problem by a process of elimination, also check the selector forks are fully fitting in the grooves on the slider gears.

Good point, thanks. I'll try this tonight.

Spent an evening playing with the gearbox, nd it seems to be a general issue that the selector shaft needs to be eased upwards when fitting the inner cover. I may simply grind a bit of a taper onto the end of the shaft to help it locate into the hole.

Thanks for the helpful comments, on to the next problem
/Steve.