The bad news came this morning, I need a 3rd OS piston ( and ring ) for my 250 Mono. I didn't find one and I am told an IT ( or YZ ) or a TS piston would fit with modif made to the cylinder and head. Quite a few post are scratching the subject, but if someone as done the job with good result I would apreciate the details. Of course my first choise would be a 3rd os TY but ... I also will change the rod , but replacement is avalable. There are 2 different type of IT piston, the one with the '' arche '' is suppose to be beter but wear faster. I don't realy use the last bit of power of the bike since I am an average rider. So TS or IT and if IT, withc one choose?

A couple of picure of IT VS std TY http://s1065.beta.ph...837536139540032

I should say that TS piston is not a problem to get .

Guy

Is the TY piston the 1 on the left in both photos, if so it looks like the deck height from the pin to the crown is quite a bit taller & to fit the other pistons would involve shortening the cylinder to allow the piston to travel to the top of the bore

Have you checked all the normal TY parts suppliers?

Looking to the future might it not be worthwhile now tracking down a better barrel while you can? Unless you've re-ported it of course.

Edited December 23, 201213 yr by 2stroke4stroke

Hi Guy, Wiseco make piston for mono, also, Mitaka make rod kits (rod kit is same as yz). Nick.

Fantnik : Thank's I will check Wiseco although I'm not there biggest fan and also give Mitaka a look

Tony : Yes the piston pin is set close to 2 mm lower on the Mono ( probably because of the 68 mm stroke vs the IT YZ TY ts stroke is 64mm ) and the skirt of the piston is also longer on the Mono. So if someone have done the mod they had to mofify the cylinder base and the also machine the head .

2stroke4stroke : Yes I'm looking for a barrel or a complete bike for parts, but here in Québec ( Canada ) they are few, and I looked all over the net to find a piston ring set.

Hopefully I will find the parts or the correct modification to do because as you can understand I can't make mistake.

Guy

Just checking - your post says TY250 Mono yet the pics with the piston pics show TY250 Twinshock.

If you have to do that much machining to fit a piston, maybe it would be easier to sleeve the cylinder and get back to a piston that is more readily available?

Have you tried B&J racing in Tennesee? They are pretty well known for TY work.

Hi Thats_a_five, if you look at the other picture you will see Mono and IT piston, machining a new sleeve with the exact porting is a lot of work since I only found one second OS for std 250 mono.

After the holiday decision time will come so ....

Guy

the mods your talking about are the basis for the 270 conversion using a 70mm piston. Ring birkettmotorsport uk importer for ossa, they have a website and lots of ty experience.