dodger wrote:Flat top pistons are correct for a Model 31 for 1960 on machines.
Count the fins on your barrels, 7 for a Model 30 and 8 for a model 31.
If you look under the cylinder head around the exhaust port you should see some small fins going of at an angle, this will identify it as a post 1960 head.
Laurie
Hello Laurie. I've taken the heads off to take photos and to confirm the stroke more exact than via the spark plug hole. The stroke is 72.8mm confirmed and this is the Model 30 spec, not the Model 31 which is 79.35mm. This tells me I have a model 30 crank
My cylinders have 8 fins which you say is for the Model 31 but what puzzles me is that at TDC the pistons are just proud of the top of the cylinders as you would expect. According to your thread they should be 6.5mm lower
The cylinder heads do have the fins as you describe but again this throws up another puzzle in that F W Neil's bible states that Models 30 and 31 top end parts cannot be interchanged. Model 30 was not marketed in 1960 whereas, if my barrels are Model 30 (pre 1960) and my heads are post 1960 then according to the FW they cannot go together
The deeper I dig the more confused I get. It doesn't bother me unduly that I have a 600 instead of a 650cc apart from the embarrassment of not sussing it out whilst I was restoring it. Should I want to put it back as a 650 would I have to replace barrels and heads as well as the correct crank?
I hope I can post the photos OK. Come on folks, put me out of my misery.
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Ride safe all.