AJS & Matchless Owners Club

As a rookie restorer of a Model 8, I hope I'm at least half way up the steep learning curve! My current issue is that on assembling the crankcase halves there is about 0.5mm side to side play in the crankshaft when pulled from the stator side. I have put shims (up to 1mm) on the inside of the left hand side crank bearing but there is still play. If I put on the duplex drive cog and stator and tighten the stator nut, the crank seizes up!
Hopefully someone who has successfully rebuilt one of these can tell me my obvious mistake.

you don't need shims, the manual says a minimum of 20 thou end float without the rotor fitted, when you fit the rotor, sprocket, spacer and tighten the nut this will pull everything towards the drive side and it should revolve okay, you do have a manual?

Kind regards Colin

Cheers for the notes Colin, good to know that there is supposed to be a bit of play in the crank before full assembly. The shaft rotates freely when the sprocket and rotor are put on with the retaining nut finger tight. As I tighten the nut the crank gets progressively harder to turn, so something must be binding. You mention a spacer, is there supposed to be one between the drive sprocket and the bearing?
I do have F Neill's manual and will sift through it again for any clues.

I am not sure about the spacer, sprocket first on the right way then the rotor, washer and nut, maybe the spacer was on another engine, old age memory is not a good thing.

Colin

There's no spacer shown on the engine diagram, I have the useful A3 size from the spares shop, so that must have been on one of your many other rebuilds?

You must have endfloat on the crank when the crankcases are assembled. Crank endfloat is controlled by the ball bearing only (and is effectively zero).

Does this diagram help?

It's worth noting that it is an unusual arrangement. The sprocket runs very close to the backplate (and is often fitted the wrong way round). Sometimes, the shims are necessary to get enough clearance.

Did you fit one roller bearing (nearest the crank web) and one ball bearing (at the drive sprocket end)?
Is the breather rotor missing?
Full rebuild thread, complete with main bearing saga: http://www.jampot.com/forum/viewtopic.php?f=159&t=22646

UPDATE.
Thanks Paul for the very useful photo and diagram, the left hand side of the crank was assembled correctly, but after stripping down and a minor rebuild I have found the cause of the friction. Tightening up the rotor nut on the drive side pulls the crank across (as it should!), causing the timing gear drive cog on the rhs to foul the crankcase. Equally mysterious.

Hmm, that's a strange one! Can't think what could cause that.

Timing side bush not fully home?

The timing side bush is flush with the crankcase, which I assume is correct. If I pull the crankshaft to the left, then the shoulder that is on the crank keeps the timing gear clear of the bush and crankcase. This shoulder is pulled just into the crankcase/bush when the rotor nut is tightened
I mght have to give it the Basil Fawlty treatment and threaten to bash it with a branch if it doesn't behave!