New piston rings enough or rebore @ 25000 miles ?

[kebab19]

Considering beefing engine up in the following order:
1) Less restrictive exhaust system & possible rejet
2) Gas flow head / replace valve oil seals
3) New piston rings or rebore
4) Bigger carbies

Engine has 39000 kms / 24000 miles and sounds fine but guzzles oil. Yes, they all do etc etc but 450mls in 200 miles is 2 stroke territory! I intend to clean up cylinder head with new valve oil seals etc, but my main Q is regarding the barrels.

Of course I havent looked inside yet, but is it unrealistic to only fit new piston rings at this mileage? Is a rebore a more realistic requirement? And if so, is 878cc the only option ? TTS the likely option?

I am hoping to halve my oil consumption as well as gaining a little more poke; doing both would be great.

[HansJ]

I did new rings/honing at about the same mileage. I also measured the cylinder/piston wear, and although within limits, it was close to the limits in the top/fwd/rear part of the cylinders. It cured my oil consumption, and to a small degree improved performance. With that said, I suspect my engine had lived a hard life before I bought it. Previous owner had put on flat-slides, Yzf- swing etc as soon as he had broken the engine in. So it might have done a lot of track sessions or such... But, my engine didn't consume as much oil as yours.

Last winter I did a complete 'make-over', new bearings, JE-pistons etc. It's much more fun, but it costed... I believe there are Yamaha OD pistons, might be worth checking out. You won't get 878 ccs and increase in compression will be very small though

[phuk72]

You can buy overside OE pistons - there is a recently started thread on here.

I would cure oil consumption first before adding more power - new rings and barrel hone may well cure you you could go oversize.

Then look at exhaust, carbs etc.

[youngy]

TBH I'd want to measure up on the ring gap and measure the bores before jumping in on a rebore.