Pistons. Yes that old chestnut

[ChequeredFlagRacing]

Doing a re-bore and the guru tells me to go for 2ma or 2rk (early ones) and not to worry about windows for the upper pistons.

So who has the part numbers please for both types

TIA

[silverstrom]

You need TZR250 1KT, 2MA, 2ME, or 2MY pistons. Yamaha part number for std bore 56.4 is 99999-02108. That gets you set of rings and 1 piston as a kit. 1st oversize kit is (+.25) is 99999-02109. 2nd oversize kit is (+.50) is 99999-02110.

Use new Yamaha pins and clips and new Yamaha small end bearings.

Yamaha only supply up to 2nd oversize. If you need bigger than that you'll need another supplier.

2RK is TZ250, but the TZ part number supersedes to 99999-02108, so that simplifies your search.

Lots of discussion on this forum about using 4 TZR pistons.

[ChequeredFlagRacing]

Thanks for the reply

[rz500guytexas]

I would put what came in the bike. Proper pistons with windows if you can locate them

[phildu31]

I would put what came in the bike. Proper pistons with windows if you can locate them

That is right when you don't understand how this motor works.
Otherwise, you can put TZR kits like I did nearly 20 000 kms ago.

[vma500]

Pistons with Windows need richer jetting and richer jetting needs more ignition advance , it makes sence now ?

Tzrs with no Windows are perfect since the ignition is all same for all the 4 pots

[V4 Stroker]

Ended up getting Mitaka TZR250 Piston Kits after chatting with Mick Abbey Tuning here in the UK
Just waiting on the re-bores to be done