Trials Australia Forums

hi just got my barrel back 4 my ty 175 after a rebore and new piston kit. the piston is a tight fit i would say i have not put it on the bike as im usure of the fit and to add to it when you line the piston up to the rings and ports the top ring opens out and jams in the port.if i rotate it a fraction it pops past a travels up and down ok but a bit on the tight side should i hone?the ring's close ok around the ring peg i cant see any over lap at the pegs to cause this.im sure if i fit it and run the bike it will brake the top ring any advice would be great. it may be just me been over cautious but it just dont feel right! ps i can't load my rebuild pics my filles too big.any way around this thanks again great site luv it

Check the ring end gap on each ring without putting the ring on the piston. It is the fit of the ring in the bore that is critical. Put a ring in the bore from the top end. Position it in the section of the bore with no ports and straighten up the ring using the piston crown as a guide so it is square in the bore. Now measure the end gap of the ring with feeler guages. If the ring locating pin goes all the way across the width of the ring, then you will have to measure the pin diameter as well to work out the true ring end gap. Most rings have a recess on each end that covers the pin and you don't have to worry about the pin diameter. Each ring must have an end gap when cold or it will seize to the bore when it heats up (and gets longer). The ideal gap for that ring material and ring diameter should be on the printed instructions that came with the piston kit.
The fit of the piston in the bore without rings on it should be quite free (clearance fit of about 0.002 to 0.003 inches depending on what alloy the piston is made of).
What brand is the piston kit? Most Ty175 pistons have the ring pins at the rear and they go to the sides of the intake port.
There are a few ways to resize your photos. One easy way is to email them to yourself. When you go to do that your email software should ask you if you want to send them as original size or smaller. Choose smaller and then when you get your email back, they will be a handy size for posting on the forums.

thanks as allways for your help