Triton Primary Chain

Dumb questions of the day.
I'm attempting to build a Pre Unit Triton.
The engine is a T120 with generator/dynamo cases.
The crankshaft is seemingly an alternator crank.
I'd like to run a dynamo.
Today I fit the crankshaft sprocket , clutch, and primary chain for the first time.
The sprocket seems to run too close to the cases, if i apply a little pressure to the chain on the sprocket, the rivets touch the case.
Is there some sort of shim or spacer supposed to be behind sprocket?
I don't see anything in the parts manual.
Are there different depth sprockets?
How much space should there be between sprocket and case?
Any ideas?
Thanks.

There should not be a shim behind that sprocket, but you can always install whatever you need to make it work with 1/8" chain rivet clearance to the case.

Thanks. Are there Triumph shims for this or basically just a washer and not a splined part?

I don’t know part numbers or details but yes, the shims should exist at a Triumph parts supplier etc. I actually thought there should be a spacer there, but it’s been a while since I was elbow deep in a pre unit Triumph.

On a Triumph the clutch centre is fixed on its taper on the gearbox mainshaft. So, correct chain alignment is achieved by shimming out the engine sprocket to suit.

Irrespective of your chaincase fouling issue, your starting point should be the same, check the alignment of the front sprocket to the clutch sprocket. Hopefully the front sprocket needs shimming out and you’ll solve two problems at once.

Dynamo 650s got alternator-type crankshafts after about 1954.