i need a 40 over piston for my 92 lt and i found a piston advertised as 68mm and wondered if that was 40 over

 

first off as you know the piston and bore sizes are in millimeters. now to CONVERT millimeters to thousandths, you have to take the millimeters X .03937 to come up with the measurement in thousandths. now the stock bore size of the 88-92 LT's is 67mm so take that times .03937 and you come up with a bore size of 2.63779 (this is in thousandths of an inch), next find the size of the 68mm bore size, which would be 2.67716. next take the 2.67716 (68mm bore size) - 2.63779(stock bore size) and it should be .03937, which in turn would be .040 thousandths overbore in thousandths of an inch, because you have to hone at least a .003 thousandths clearance for the rings

so yes a 68mm overbore size would be the same as .040 over, i hope you can use this formula for the future times. and being a machinist this is easily second nature to me.

remember to get from mm to thousandths use this formula (mm X .03937=thousandths of an inch)

oh yeah and the .03937= 1 millimeter

later on
NichelsonRacing87

 

wiseco .com should have all the info you need

 

you still might have to convert them over, i just gave him all the info he asked for and i even gave him the formula to try it himself and use for future purposes.

 

that piston is to big for your 40 over bore

 

i would call wiseco,and just ask if .040 over is the same as 68 millimeter

 

67.25mm = .10 over
67.5 mm = .20 over
67.75mm = .30 over
68 mm = .40 over
68.25mm = .50 over
68.5 mm = .60 over
68.75mm = .70 over
69mm = .80 over
69.25mm = get a new sleeve

 

69.25 mm is not get new sleeve but start using YZ250 pistons I am at 69.50mm no problem bro
k-dog

 

yeah correct man, hey trickeytech, why do you say that 68mm piston is too big for a .040 over bore???? yeah you could call wiseco or take it to a shop, but alot of guys are dumba*** these days and they do not make the thousandths size into millimeters, as i said i bore quite a few of these out and have not ever had a problem with making it the right size. 68mm is the correct piston size for a .040 over bore.