A forum for owners of Yamaha TTR250 trail and enduro bikes!

Gabriel2fifD · Member

Should I get OEM or aftermarket for timing chain, chain guides, Piston and rings

mossproof · Super Guru

I would be wary of aftermarket engine internal parts like cam chain and guides, having had bad experiences of ill fitting and poor quality, so for those I would definitely go OEM.
For the piston, OEM is fine, but Wiseco and Wossner are both good quality makes that I have used in the past.

Gabriel2fifD · Member

Thank you mossproof do you know if new OEM parts from a 2000 TTR250 are compatible with a 1995 TTR250, I have found this Yamaha parts dealer https://yamaha-motor.com/motorcycle/TT-R250/2000 but they dont have any parts for a 1995 they only have parts for a 2000 and onwards

mozzy · Member

Hi ive just fit a wossner first oversize,had it bored and honed, the piston is quality lightweight racing,Try and buy all the parts you need from the ttr shop Steve only sells quality.

Blacknight · Member

I'm doing a top end rebuild on my 1999 blue TTR and wondering about aftermarket piston kits and head and base gaskets. The Wossner and Wiseco piston kits cost over double what the OEM one costs here in South Africa. Is there a definitive advantage to fitting aftermarket or why are they so popular?

Then, the aftermarket gaskets look "cheap" compared to the OEM, especially the head gasket. The OEM is some laminate steel affair while the aftermarket looks like "paper". Anyone have good or bad experiences with either?

Any experinces with valve stem seals, OEM vs aftermarket. Like with the gaskets, is either definitively better or worse than the other?

I'm having to do the repair because of a slightly too small main jet for the piping hot ambient temperatures here in summer. 35 to 40 deg C.
Besides fitting an oil cooler are there any other ideas, like piston choice and jetting, that may have an influence on how cool the engine runs?

-- Edited by Blacknight on Tuesday 13th of October 2026 07:15:38 AM

mossproof · Super Guru

Unless you are fitting a higher compression "performance" piston, Wiseco, Wossner or OEM pistons will be as good as each other I think. Go with what is cheapest and available.

Aftermarket gaskets and seals can be a bit of a lottery - you don't really know the quality until it fails, so if anyone can recommend a brand, go for it, otherwise I would stick with OEM. I have had good experience of Cometic gaskets, which Steve sells, both standard and for the 350 kits, but I always use genuine Yamaha valve stem seals.

Richer carb jetting should bring the combustion temperatures down I think. An oil cooler will also have an effect, and if you are running a large sump guard/bash plate, drill some holes in it to allow cooling airflow around the bottom end. (This has dropped the oil temps by a couple of degrees on an xt600 I know of!)

Blacknight · Member

Thanks mossproof!
My thinking exactly. I am happy with the engine's performance so no need to up hp via whatever means. Nothing is available locally, and the OEM piston is substantially cheaper, so I'll go with that and the gaskets and valve stem seals all from Yamaha. Good tip on the bashplate holes - I haven't got one fitted but need to get one so will perforate it nicely after I also increase jet size. These bikes are not very common in these parts and the OE/Raid, etc models even less so, so getting a used oil cooler will be difficult. I may look at plumbing in something from another bike or an universal unit.

mossproof · Super Guru

Going off-topic here, but the main oil cooler thread is here:

ttr250.activeboard.com/t44874914/oil-cooler-information/

Important to fit the correct length blanking bolt inside the clutch cover.

Blacknight · Member

Thanks mossproof! Noted!