250 bore measurements

[X2guy]

The specs in my claymer manual for std. bore is 66.020 to 66.040 with a wear limit of 66.070. It doesn't say anything about over sizes. I am .5mm over. What specs should I compare my bore measurements to? Do I just add .5 to the above measurements? (66.520 to 66.540 with a wear limit of 66.570).
Thanks

[RideRed250R]

isnt .5mm 20 over? 1 would be 40 1.5 be 60 2 would be 80 isnt it??? it hink thats wat ** askin right?
adam

[X2guy]

Your right but that's not what I'm asking. What I need to know is what the bore diameter should be at 0.5mm (.040").
I am putting a long rod crank in my 86 R and therefore I need an 89 piston or spacer plate. I'd prefer to go with the piston. Before I throw in a .5mm oversize 89 piston I want to measure the bore to see if it's worn past the limit. If so I'll bore it out to the next oversize.
Thanks

[TimSr]

The specs in my claymer manual for std. bore is 66.020 to 66.040 with a wear limit of 66.070. It doesn't say anything about over sizes. I am .5mm over. What specs should I compare my bore measurements to? Do I just add .5 to the above measurements? (66.520 to 66.540 with a wear limit of 66.570).
Thanks

Just add .5 to the measurement. A 66mm standard is piston size, and the other .02-.04mm is the clearance between your cylinder and the piston. The clearance specs are the same for an oversize piston, or other cast pistons, but keep in mind the clearance specs for a forged piston, such as Wiseco are slightly higher.