Griffon 380 rebore sizes?

[Kim275]

Hi does anybody know off hand what the over bore sizes are for a 380 griffon?

I now need a rebore on my QUB and need a new piston- but for speed I have a spare barrel which has already been rebored when I got it - (without a piston). It measures 82.3 mm - with vernier calipers.......I reckon 10 thou' of an inch is .25mm - so is this the first rebore?
Cheers Kim

[John-Boy]

The books say that the 380 over bores were 20, 40 and 60 thou (the 250 was in 10 thou steps)

Standard bore is 82mm - plus 0.020" is 82.5mm.

Perhaps your cylinder was re-bored with the expectation of a 10 thou piston being available, allowing some running clearance?

If you need a piston, Simon Bateman has some with two thin rings instead of the Dykes ring, he may be able to supply a plus 10 to fit your cylinder.

[Kim275]

Hi John,
Thanks for this........I measured 82.3mm but only with a very old set of vernier calipers - so likely that this one is at first re-bore 20 thou = 82.5mm.....
Will check with Simon on what pistons he has in stock tomorrow.........I agree on them being good pistons - as I had his standard 82mm piston in - and had just fitted a new set of Wiseco rings - and it worked well.........up to the point when an "engineer" rebuilt my small end - left the bearing too tight in gudgeon pin - without drilling the oil holes...........as a result - lots of heat and a circlip popping out and running up and down piston, bore and head...so bit of a mess at the moment - ... ...hence need to either bore out current barrel - or use my spare....and hopefully have it ready for Marks Tey.

Thanks again for your help
Cheers Kim

[John-Boy]

Kim
I still have my old 82.5mm Griffon piston with the Dykes ring, you are welcome to it if you need it.

When I took the piston and barrel to Simon for a rebore, he said it wasn't worn enough but I replaced the piston anyway for peace of mind.

You might feel happier with a new piston but they are pretty expensive. If you want it, send me a PM with your address and I will put it in the post.

[Kim275]

Hi John,
Many thanks for your kind offer. Just spoke to Simon - and he is shipping a new 82.5 - so hopefully I will be sorted.
Cheers Kim

[John-Boy]

Kim

No problem, I am sure you will feel happier with a new piston.