Will pistons fit

kwackman12 · Post by **kwackman12** » Fri Sep 11, 2009 7:32 pm

Been offered a set of barells & head that had Yamaha tz pistons fitted pt no 59w-11631-97
I have a set of 26j-11631-00-97piston's does anyone know if I can use these instead?

the-elf · Post by **the-elf** » Sat Sep 12, 2009 9:40 am

If you look on MJ Team sparrow site the info on the deck height for the various TZ pistons is all there. You may need to get some machining done to match the different pistons. You'll also need to get the head machined to match the dome radius and get the squish right as well.

mgtkr1 · Post by **mgtkr1** » Sat Sep 12, 2009 4:58 pm

both 59w and 26j pistons are a straight fit into kr barrels. differences are the cutaway and head profile between the 2 differing tz prefix models. only thiong you woulds need to do is get the head matched for optimum performance and reliability. getting a bit harder to find these days, esp the 26j but are essential for a engine with highly modded ports. there are other alternatives but using the tz pistons is easy and proven. you will also need to replicate the oilways of a std kr piston with a good drill,steady hand and bloody strong nerve!!! 1rk rings fit the 59w which is quite easy to obtain however the 29j piston requires a ring compatible with nicasil, the 26j barrels are chrome i think? early yz125 rings can be used, with the prefix 5x4------.. i will dig out an old packet for conformation.hth
yep, part no is 5x4-11611-02. american ebay usually has a few. if you dont want the barrels or decide to flog them on let me know as i would be intrested. you can use either 26j or 59w pistons. show us a pic if you can, intrested to see the ports particularly the tranfers. cheers.

mj43 · Post by **mj43** » Sat Sep 12, 2009 9:03 pm

26J and 59W are interchangeable no machining required.
Can be used with a stock head but for best performance needs to be re machined.
Crown height is the same on both and very close to stock. Dome radius 150mm on 26J and 59W 120mm on stock
Running stock head would mean lower compression and lower squish velocity

mgtkr1 · Post by **mgtkr1** » Sat Sep 12, 2009 9:38 pm

26j and 59w share the same head shape then mark? that makes things straight forward then.

mj43 · Post by **mj43** » Sat Sep 12, 2009 9:42 pm

Check what size the pistons are
Think both come in 96, 97 and 98 variants
Use the correct size to avoid too tight or too much slap