9 replies to this topic

[miniman86]

hi, ive just bought what i thought was a standard 1275 to rebuild but i dont think it is a standard 1275 after all!! the pistons measure 72.95mm across if that helps? i know my mates 1380 engine pistons are 73.5mm across. so does that make mine around a 1330-1340ish? cheers, alex

[Jammy]

This page will tell you all about bore/stroke sizes and there resulting engine cc's.

Are you sure its definitely 72.95?

[miniman86]

its about that, but it was measured using an old vernier!! so could be 73mm.

[Jammy]

Measure the bore of the cylinder instead of the pistons. I think 73mm was quite an old piston size that isn't used much anymore?

[miniman86]

ok cheers. but on looking at that website it must be around the 1340 mark. i paid £150 for the complete engine and gearbox. not bad huh!

[neil_g]

also depends on the stroke though..

chances are that its an old 1275 that needed a slight bore to freshen the cyclinder walls up?

[Dave the Rave]

Does it say anything on the top of the piston?

Most bigger pistons say the size or +0.060" or whatever. Are they dished or flat top or look anything special?

[miniman86]

i think theyre dished, but ive got two 1275 blocks, 1 i had spare in the garage, with crank, con rods and pistons, and the new 1 i bought at the weekend. ive offered the new pistons upto the old block and they don't fit at all, theyre 3mm bigger diameter than the standard ones. that any help??

[Dave the Rave]

All i would say is measure or have someone else accurately measure the bores of the "bigger" block and look at the website jammy basturd put a link to. Also try to identify the crank. I guess that's all you can do to find out the size really?

[miniman86]

ok cheers. is there any way once the pistons are back into the block to measure the diameter of the bore then measure how far down the piston goes, times that by four and work out the CC that way?