Cam chain length

Hi can somebody advise me as to which cam chain I need for a 1972/3 honda st70. I bought a cam chain kit with rollers etc. When uve come to fit it I can just get it on without then oil pump drive gear on so it is obviously too small. Which length do I need please?

i believe this is what you need http://www.ebay.co.uk/itm/nos-honda-s65 ... 1409665192

Personally I'd buy a DID they make great chains.
I think the equivalent is a 25Hx82 but most decent suppliers will confirm this.

Sounds like you need a parts manual?