What size do I bore a DT/TY250 cylinder

[tony27]

I'm about to get my TY250 cylinder rebored & need to know what size it should be done to.
The piston is for a DT250 etc #311-11635-00 & is stamped 7025 on the crown, is this the size to ask for or should there be clearance on top of that?
Using a set of electronic calipers the piston measures about 69.95 just under the bottom ring & about 70.2 at the base, I've never seen that much taper on a piston before which is why I'm not sure on what size the bore should be

[Colin Jay]

When having a cyliner rebored, it is not bored to a nominal size. The bore is bored and honed to the size of the individual piston plus the required piston clearance. For example, if the piston measure 70.00mm and the piston clearance required is 0.05mm, then the bore is bored and honed to 70.05mm. This is why when having multicyliner engines rebored the piston are alway (if you use a reputable mahcine shop) matched to an individual cylinder.

Just take your cylinder and piston into the machine shop, and they will measure the piston, then bore the cylinder to the size need to give the required piston clearance. If you have any doubts, ask them if they have the specific piston clearance for the TY250, if possible find out the required piston clearance yourself and tell them what clearance you want.

CJ

[Freakshow]

What he said.  the piston you have is a .25 or first over bore, so its to fit .25mm over the standard TY bore what ever that is

[tony27]

Manual I have says 70 is standard with max allowance of 70.1 before boring

[Freakshow]

take the piston and the barrel to your borer and ask for 20 thou clearance, they will do the rest.

[matcho mick]

whoa err 20 thou freaky,u mean 2 thou,20 could rattle a tad ,