AMC gearbox

The sliding gears need to slide freely , Inspect the splines with a magnifying glass for rough surfaces ,I had to "fettle" mine to get a light gearchange action.

I've used the same (excellent) Dvd to dismantle/refurb my laydown gear box. Based on what I found I agree with Robert the gears should be an easy sliding fit on the shaft/splines - and in any rotational position. If they will fit in only one orientation on the spline there's something wrong IMV.

George

Slightly bent shaft?

If we are talking about the extreme R/H gear on the mainshaft and the extreme L/H one on the layshaft then this is mainshaft 1st and sometimes incorrectly, layshaft 4th (as it has nothing to do with 4th gear; it just happens to be the 4th gear on the shaft!).

If these are tight on the splines, this is not generally a problem as they do not slide. The mainshaft 1st gear is held against the inner cover bearing when the mainshaft nut is tightened. If there are wear marks on the face adjacent to the bearing, the nut may have been loose at some point. Sometimes you see a "shadow mark" even if the nut has been tightened and the box has not been stripped for a while.

The layshaft fixed pinion is not retained by a nut so a tightish fit could be seen as an advantage.

It is a little odd that the gears will only fit in one position but this is probably just a burr.

If it were my box, I would check that the free rotating gears that are retained by the fixed spline pinions can rotate freely when fully assembled and not worry unduly about the tight fit of the splines. I would point out that on some other British bikes (they all work on a similar principle, even Velocette but typically back to front!) these splined gear are a deliberate press fit.

I fully agree with the comments that the sliding spline pinions must slide freely. Any tightness here will dramatically influence the feel of the gear change.

Removing the tight bushes should be straight forward. A stepped mandrel is always the best option. A socket or bit of tube slightly smaller than the bush OD is a fair alternative.

I seem to recall that the high gear bushes go up against a shoulder (it is a long time since I have changed the bushes on an AMC box but I am sure that someone can confirm this). You are left with the options of using an expanding mandrel type bearing remover if you can beg/steal/borrow one, or carefully split one bush along its length using a Dremel or similar. the second bush could then be pushed out with a suitable sized tube/mandrel.

A couple of warnings on the high gear bushes. New ones easily close up when pushed in and may need reaming out to fit the shaft. Secondly, if the old bushes are worn, there is a fair chance the shaft is worn as well. It is pointless fitting new bushes to a worn shaft. A bit of measurement required.

I agree that the gear bushes should be free spinning. These should not close up. Sorry if I didn't make it clear. I wouldn't recommend heat on the sleeve gear either.

I am now doubting my memory on the stepped inside of the sleeve gear (as I said it was a while back). Looking at the options available it appears that there are two lengths of bush and you can fit the longer bush without modification. This would suggest a plain bore all the way through. Pressing both bushes all the way through would be the best option.

I have always pressed sleeve gear bushes in with a press and mandrel. Oil the outside of the bushes first. It sounds silly as you would think the oil would get scraped off as the bush was pushed in. You will be surprised at the difference it makes though!

Bushes soaked in oil for 24hours before fitting.