Yamaha TRX850 Enthusiasts Forum

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.

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

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.

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