Mk3 Primary Chain Alignment

Hello to all.

Question, has anyone else found this?

I've fitted the Primary Inner case, which is fixed to the crankcase. (the case steady was not done up, as yet)
the drive sprocket, which is located by a Morse taper and key,
the clutch basket onto the gerabox shaft, which sits up against the circlip,
The clutch basket had 2 shims between the piece that sits against and over the cir clip and the back of the basket. (this is shown in the manuals like this, and is how it was dismantled)

Then it says to use a straight edge and check the sprocket alignment.

The best way I could see to do this was to use a straight edge over the clutct basket face and measure the dictance to it's teeth,
then measure the distance to the drive sprockets teeth from the straight edge still on the clutch basket.

The clutch needed to go in by 5. something mm.

So I took the 2 shims out behind the clutch basket and re measured, now it was only out 1.3mm.

But the clutch basket rubbed on the raised piece on the inner case where the gearbox shaft comes through.

It was rubbing on the edges of this section, the back side of the clutch basket has shamfered edges around the hole for the gearbox shaft. The chain case has 90 degree edges.

So I ground the 90 degree edge of the chain case to match the shamfered edge of the clutch basket.

Now it doesn't rub on the chain case, but it's still proud 1.3mm.

It can't go in any more, can it ?

I think 1.3mm out of line shouldn't be a problem ?

Graeme

No, 1.3mm wont cause a problem. It's probably a closer tolerance than most people run them at, and a chain is very forgiving when run slightly out of line. I would have thought that you couldn't (acurately) measure to a much closer tolerance than this without going to an awful lot of trouble.

When I was setting my belt up, I found that rotating the gearbox mainshaft 90* at a time very slightly altered the plane of the outside edge of the clutch basket, which with a straight edge going forward towards the drive sprocket altered the measurements ( very slightly) that I was getting. This has been discussed before, and as far as I recall, it is the runout of the mainshaft that causes this 9and is the same princiole for a chain fitment).

So as I said, if 1.3mm is the correct measurement, fit it at that, the only puzzling thing to me is that you have had to resort to grinding the chaincase? Are you sure that the chincase has been fitted square on the crankcase cheek and not angled outwards at the rear? It shouldn't be as you have not tightened the mounting point up, but make sure that it is square!

Reggie, thanks for your input.
The chaincase was square and bolted up to the crankcase and the inner case support bolt was loose and not affecting the chaincases fit to the crankcase.

This is the inner side of the clutch basket, see the shamfered (45 degree) edge to the hole for the gearbox shaft.
sorry for the crap pics.




This is the start of grinding the 90 degree edge of the inner chaincase to allow the clutch to move closer to the gearbox.
(dremmel)



The clutch basket can wobble on it's bearing but I could hold it with pressure in the center and could feel the bearing was square.

You can check the alignment really easily with a home brewed tool made from four screws in a piece of wood. Set the screws apart so that the heads of two will rest on the crankshaft sprocket edge and two on the teeth of the clutch basket.
Set them all level on any handy flat surface - kitchen worktop is good enough.

Very cheap, very easy.