SQ4 Primary drive

[will_curry]

It's quite possible. Some years ago I bought a new pattern rear brake drum and sprocket
for my Square 4 which was so eccentric it was completely useless.

The only way I can think to check your chainwheel is to dismantle the primary drive, mount
the chainwheel in a lathe and measure it Quite what is an acceptable eccentricity I don'tknow
and I'm not in the position to check a genuine one at the moment.

[nevhunter]

Very little eccentricity if possible or the chain will rub the lugs on the bottom when it's most slack. With the clutch and outer cover off release the large spring in the cush drive and check the variation of chain tension as the chainwheel is Turned. The gearbox mainshaft doesn't turn when you do this. Also try to pull the rear chain tight and see what effect that has on the front chain tension .All this has to be made right. Nev

[will_curry]

The only problem I can see with an eccentric chainwheel is that the primary chain can't
be tensioned correctly - at one extreme it will be too tight and at the other so slack that
it hits the chaincase. If you can set the tension of your chain so that neither of these happens
I wouldn't worry.

In my opinion most people set chains too tight anyway. A chain that is too slack will hit the
chaincase and will snatch as you open end close the throttle. A chain that is too tight will
wear itself and the sprockets very quickly, sound very noisy and make the gearchange
very difficult.

Set up properly and lubricated the contents of an Ariel primary chaincase will last a very
long time. In my experience the engine shaft shock absorber will fail long before the
chain and sprockets need replacing because the chain is worn out.

[xavier.devars]

Hello,

After a thought, I don’t think it is the clutch wheel. Conditions are : gearbox in neutral, clutch not moving, turning the rear wheel.
The mainshaft turns with its sleeve within the clutch center and makes the clutch wheel/basket/center move eccentrically, as if the shaft was bent, but it is a brand new one, and it was doing the same with the old one (I changed it because of this).

Regards

[Paul_Linden]

Both my square fours do the same, by a very small amount. I put it down to the rear chain tension not being constant due to a stretched section or stiff rollers.

[paul.jameson]

From your descriptions of the problem, the only things I can think of which could be at fault are the drive end bearing in the gearbox or the two bushes inside the final drive gear.

[will_curry]

I suppose it's possible you've managed to get hold of another bent mainshaft but it's a
bit unlikely.

As Pete says there is always a little movement when you pull on the rear chain but it's
usually only thousandths of an inch and it occurs in the big ball bearing in the gearbox.

All I can add to Paul's list is that the inner bearing surface for the clutch needle rollers
on the later GB gearbox is a separate part from the mainshaft. I suppose it could have
become damaged in some way and now not fit on the mainshaft properly. On the earlier
BA box it's made in one piece with the mainshaft so that can't happen.

Can you measure how much the chainwheel is moving when you turn the wheel?

[nevhunter]

Is the chain made from two different chains? Nev

[paul.jameson]

Your reference to the sleeve was, I assumed, to the part Will refers to which forms the inner bearing surface for the needle rollers. I suppose you could have meant the sleeve gear and that you might be using the original inner bearing surface for the needle rollers. Can you clarify please?

[xavier.devars]

Hi, I am away from the bike right now, but I’ll make some measurements next week. I think eccentricity could be around 1 mm.

Paul, yes this is the sleeve which sits between clutch center and shaft. It is brand new from Draganfly, but you never know.

I will check the chain also, as I can’t remember exactly (several bikes at the same time).