Is it A7 or A10?

[Martin]

Hi, maybe stupid question but because I do not know the history of the motorbike, only that it was build from parts in 70s maybe it is not so obvious.

Today I have tried to fit the original air filter box and the rubber hose for A7 but I think I have a problem.
Can I check somehow if the engine (barrels) are A10 or A7 without disassembling the head?
Some quick measurement or unique characteristic which gives me a confidence what engine do I have.

(engine number starts with AA7, but as mentioned the engine can be mixture of A10 A7 if it is possible)

Thanks you
Martin

[berger]

A7 seven fins

[muskrat]

G'day Martin.
As berger said the A7 has 7 fins on the barrel, the A10 has 8 fins. So the A10 motor is roughly 1/2" taller and uses a different rubber.
Cheers

[Swarfcut]

 Martin.  Find the cylinder head gasket, count down the fins on the barrel. What bergs means is an A7 has 7 fins on the barrel.  A10  has  8.

 The cylinder head casting number also identifies the engine size. For early narrow fin iron heads 67 381 is an A7  head.  67-251 is A10  The numbers are on the underside of the inlet manifold. As the external dimensions and bolt holes are the same, mix'n match is possible as a worst case bitza purchase.

 Plunger air box is the same for both engines. Rubber elbow hose is a different moulding for each to accommodate different barrel heights.

 Musky's quicker on the keyboard, cheers fella.

 Swarfy.

[Martin]

Thanks for the answers.
So now it is clear the cylinder is from A10 but the crank case is A7. Hopefully it will run and I will not have only troubles with the motorbike.

[Rocket Racer]

perfect answers for a bitsa motor... my A10 runs a shooting star head and a shortened barrel, but I think I'd be sprung if I tried racing it as a 500 
The 500's are  far smoother to ride than the 650.  A star twin is a real sweetie. If you ever rode one of each they are chalk and cheese.