Does anyone know. Can I take my 1986 Yamaha TY350 cylinder and have it bored out. And then use it without new chrome? Is the material under the chrome hard enough to run a piston in?

Alternately. Will a TY250 top end fit on the TY350 block?

Thanks.

TY350 cylinders are chromed, there is no liner beneath the chrome so you will need to have it rechromed by someone like Langcourts. Cost looks to be around 140gbp going off Splatshop's site

No idea whether the 250 topend will fit but I'd suspect that the 350 is in effect an overbored 250. Going to a 250 topend if it fits isn't going to solve all your problems as getting pistons for them sounds to be a major problem

Thanks Tony.

I thought the 250's might be easier to find pistons for. I live in Canada. There are some platers closer to home that look promising. And an outfit or two that instals liners. It seems like the place to start is the piston. Does anyone at this forum have an old 350 piston, pics of the piston or blueprints of the piston. I need to know the specs for the skirt ports. Is it common for trials bikes to have both skirt ports and reeds??? I thought it was usually one or the other.

Hi oilmanincanada

Where, in Canada, do you live ?

I have a couple of TS TY and a 250 mono for witch I am looking for a 3rd os piston with no luck.

Guy

guy53. BC canada.

Try ebayuk. You should find 250 pistons there. In the end I may part my 350 out. Or do a Frankenstien with another motor. A four stroke would be nice. If I rebuild. USChrome looks promising. Or if I go with a liner instead I'll have more options on rings and rebores. Yamaha R1 pistons sound promising but will need an hour or so at the machinist to mod them.

If someone has an old 350 piston. Even a damaged one. I could use measurements on the skirt ports. Location of grudgeon pins etc.

Oilman, you should contact Mongoose Machine and Engineering in Vancouver. Top guys and good reputation.

Thanks Steve!

Thats a good lead. I'll take my cylinder in for them to look at next trip through the big smoke! That is if I can afford the ferry ride ;-)

I could use a good local shop for crank over huals too. Last one went all the way back east.

In the mean time I found a guy parting out a 250 in Winnipeg. So I may buy the top end off that. The piston looks good. If the top end does not fit, it should sell on ebay quick enough anyways. Not much mono shock parts on ebay lately.

The TY Mono 250 and 350 top ends are completely interchangeable. We could only buy the 350 in the late eighties in North America and most top experts would buy the 250 cylinder, piston and cylinder head before leaving the dealership with their new bike.

The TY Mono 250 and 350 top ends are completely interchangeable. We could only buy the 350 in the late eighties in North America and most top experts would buy the 250 cylinder, piston and cylinder head before leaving the dealership with their new bike.

Was the 250 considered better ?

I'm not a trials rider. I wanted this bike to deal with our Pacific Northwest rainforest trails. And these older trials bikes still had a bit of a seat. Tractor like torque would be on my wishlist. I recently had someone give me an 1981 RM125 basket case. He melted the piston circa 1990. So I got it going, but its kinda like riding a Thoroughbred, where a mountain pony is whats needed.

I got lucky. I found a guy parting out a TY250. So I picked up a great top end. And a fuel tank. Those were the main stumbling points for my project. I still need a front brake baking plate. But at least the needed parts are getting smaller now ;-)

Good for you, I don't think you will be sorry mov to go ing to the 250, the 350, from what I heard is hard to '' jet '' properly in different wheater and altitude.For the brake plate, maybe this can help if you don't find a plate http://www.trialscentral.com/forums/topic/44335-ty-yz-brake-shoes/

Guy

Excellent info guy53. I bookmarket it. I have quite a few old yamahas parted out. So I'll go through the bins of baking plates and see what I have first. If not, its a great excuse to buy anouther dead bike for parts!

Lately I have been buying up newer bikes with blown motors. Seems to be a lot of them about. And for under $100 bucks you usually get nice Renthal bars, fancy throttle assemblies and a ton of bits n pieces. I just grafted 1991 YZ125 forks and triple tree and swing arm onto a 1976 Yamaha XT500. Just need to find the right looking dual shocks for the back. It should look something like an HL500 when I'm done. But better ;-)