Junglejeff,

thanks for the reply. One major problem with piston replacements is weight change. The yz piston is 30 grams heavier than the TY so unless you do some major magic, it’s gonna vibrate like hell.

I’m about half affraid to open the box from B&J as he has it apart and says he cant’ figure out what to do

If I can make the special tools to put the cases back together I will try that. If not, it’s going to get sold for parts. Nobody is gonna hold my engine for ransom any more

Going off the number on the piston I would assume it is a wiseco piston, the UK expert in TYs uses wossner which may be lighter. Either way they are lighter than the #311 pistons often listed as fitting TY250s which crash into the crank due to being thicker walled & not tapering up at the edges

TY motors don't require any special tools to assemble apart from a clutch basket holder

Have you looked at getting another crankshaft off eBay if your's is bent?

You're definitely having a bad time with this motor, I didn't even need to do the crank in mine which had sat for years, was still on standard piston & cleaned up to 70.25mm no problem

There are a few areas old TY's suffer from.

The first is from hamfistedness.

The crank is a very tight fit into the main bearing, mag side and some owners have been known to wallop the end of the crank to get it out.

This obviously isn't good for the crank, even if you leave the nut on the thread and you can actually bend it or knock the alignment out.

If you haven't the tools to press it out, it's best to heat the case up a bit so the crank and bearing come out as one, then a puller to remove the bearing from the crank.

 

Another areas worth checked, particularly after a rebore is the chamfer of the transfer ports.

They need a good chamfer top and bottom otherwise the piston catches.

I suffered and found this out myself a few years ago. I did a rebore and new piston and it rattled from the off, not your normal worn bore/piston rattle, but a loud metallic knocking rasp.

When I pulled it apart I found chips of metal in the bottom of the crank and some impact marks on the piston edge.

Checking the bore and it was clear the piston had been catching the edge of the transfer ports.

 

Edited August 6, 20197 yr by goudrons