Topic: Piston ring size

[Dave B]

Can anybody please advise
My bike has standard size pistons
When i place the existing piston ring about one and a half inches down barrel i have .6mm gap where the ring ends meet.
The barrels are good and i am thinking of fitting oversize rings as compression is poor.
Can you suggest what size i should fit
Cheers,
Dave.

[bryanj]

You can not fit oversize rings to a standard piston in a standard bore.
If a standard NEW ring has too big a gap you need a rebore with correct oversize piston kits

[Dave B]

Thank you

[Wannabe Racer]

Hi Dave B.
I'm having my K6 engine rebuilt by D&M Engineering at the moment. They honed the bores for me and showed me the darker areas that were revealed. The wear is possibly only 10,000... They said I could ignore it but it will smoke a bit. The engine had done less that 30K miles.
Their advice - Rebore and fit 0.5 oversize pistons.

Cyclexchange.net have 3 0.5 oversize piston kits (I think the cheapest is $159).
bryanj is absolutely correct, if the wear is that much. If the wear is that extreme, you have no option but to rebore and fit oversize pistons.
Sorry mate, not great news, but at least you now know how to fix it.

[david 750f]

Hang on, 0.6mm is around 0.015 inches. That's within Honda limits, especially if the measurement was taken with used piston rings. The lack of compression could be something else, did you do a leak down test? Was the bike running? Could have been sticky rings.

[bryanj]

Thats why i said standard NEW ring

[newday777]

But you need to use a bore dial indicator to check up and down and all around for uneven bore.

[bryanj]

Yes if you want to spend a fortune but a ring ar several positons in the bore will tell you if its worn out