RD400 Daytona clutch

[car91r]

Ok. This had me scratching my head for a minute. Finishing up my Daytona engine and found something unusual. First, I have 2 complete Daytona engines. When checking the clutch basket I noticed about 4mm of slack between the gear and basket. So, I pulled the clutch from the other engine which had no slack. Great! Just swap. When I was assembling the clutch, I noticed the clutch hub seemed to bind against the basket. Upon closer inspection, I noticed the gear from the spare engine was thicker than the one I was replacing. 15mm vs 12mm. What! The assembled clutches work fine, no binding, in the engines they came out of, but won't interchange. Is this normal or is one maybe from a different bike. Same part number in both baskets, 02K0-1#C-1.
One other question. Are the rubber O rings that go with the fiber plates necessary or can they be left out. Thought I read somewhere that they were not needed.

[SoCal250]

Both engines are 2V0- ?
Are both gears 66T?

Strange because the 76-78 RD400 1A1, 79 RD400F 2V0, 79-80 RD400F/G 3J7, RD400 3M4, and RD400 2R9 all used the same part according to my Yamaha records. 1A1-16150-00 was superseded by 2R9-16150-00

[car91r]

Both are 2V0 engines as far as I can tell. One has the number stamped, the other does not. The one without the VIN stamped is the one with the wider gear. It does have the center case bosses that hold the exhaust butterfly actuator, so I assume it is truly a 2V0. Maybe a later spare, hence no VIN? Both are 66 teeth. Either basket will spin on the crank gear, the wider one just binds on the clutch hub.

[1976RD400C]

I looked at a couple spare 1A1 400 clutches and they are 15mm wide gears. Crank gear is about that wide too.

[85RZwade]

Love a good mystery!