TY 250 piston rings

[crash n bern]

Are the piston rings for a 74 TY250 the same as DT250 and YZ250. Also which years would be the same, ie. IT250 etc. And pistons while we’re at it. Aside from eBay, does anyone stock them. My piston has 7025 stamped on it, so I assume it would be .025 oversize.

[sleepy]

There are some differences in ring around that time. Your piston having 7025 could mean it's an aftermarket, have you looked at the underside of the piston for any markings. Wossner and Wiseco do pistons that fit TY ,DT, MX and YZ from 1973 to 1979 but there rings are different to original.

[crash n bern]

Thanks, no I haven’t looked underside of the piston as I haven’t pulled the barrel off yet. Just wanted to make sure I could get parts before I pulled it all apart. There’s no hone marks left in the bore.

The bike ran when I parked, but went under in a flood a few years back. I drained all the water and oiled her up as best I could considering both my sheds went under and I had a mammoth task. I focused more on my expensive bikes.

My son was showing some interest in it so I pulled it out and thought it’s probably about time to get it running again.

[tony27]

Easiest way to tell if it's a TY piston is the top ring is L shaped & comes up to the top of the piston. According to partzilla's part numbers they only fit TY250s & are unavailable from Yamaha but using the part number there are a few sets in the US
https://www.ebay.com.au/itm/203011148037?hash=item2f44684905:g:414AAOSwEute18n5&frcectupt=true
Be aware is you do go down the new piston route that sellers will say that the type 311 piston fits, it doesn't clear the crank without modification & is quite a bit heavier. TY Trials.com in the UK supply Wossner piston kits for YZs of the same age, they have the arched cutout instead of windows but work well or John wouldn't sell them, only things is that like all aftermarket pistons they're only available in 0.5mm increments meaning you'd need to take the bore out to 70.5mm

[sleepy]

The Wossner pistons are readily available in Australia from a couple of sources so no need to go to UK.
The last TY barrel that I bored was still stock bore but it was worn so much that it had to go out to 1mm oversize to clean up. Don't be put off by .5mm oversizes as most cylinders are worn to a point that .25mm won't clean up the wear and require going to .5mm anyway. If you pulled the motors apart on a regular basis and checked the wear as per the workshop manual you would have half a chance but a lot of these motors have never been apart since 1974 and been flogged almost to death.
Best thing is to take the barrel to however you trust to bore it and get them to measure or trial bore it before buying a piston that may not fit.   

[crash n bern]

Thanks guys, I’ve been googling to see what I could obtain. I’ll pull the barrel off and have a better look at it. It might be still in spec.