Cylinder measurement out of spec . . .

[robwbright]

I recently did the top end in my 2002 RM 125. The cylinder measured .0004 (4 ten thousandths) out of spec front to back and side to side - i.e. its a bit bigger than it should be according to the Suzuki manual.

There was about 1/8 inch of "blowby" on the piston below the ring. I don't know if this was caused by the cylinder wear or ring wear since the top end hadn't been done for 7 races.

Anyway, is the fact that the cylinder is .0004 out of spec a serious problem? The bike still runs good and seems to have good compression . . .

By the way, we used a tool dad brought home from the power plant - I'm not sure what its called. Shaped like a "T" handle with two spring loaded arms that pop out when released. Then you lock it, pul it out and measure with the accompanying gauge. We were able to get about 1 1/2 to 2 inches into the cylinder.

Thanks
Rob

 

[nickyd]

those tools aren't the BEST for measuring you cylinder out of round - you really need a bore gauge to get it absolutely right - that being said, .0004 is probably the amount of error you'd get from using those expanding gauges. isn't that a plated cylinder? as long as the plating is fine I'd go with it...

 

[robwbright]

Yes its plated and it looked fine, although I reassembled it without honing or anything - 1st time I had done the top end since buying it and didn't know any better until I looked on here the other day . . .

Oh well, lesson learned.

 

[Eric Meyer]

Rob,

the tool you're referring to is called a Telescoping Gage". It usually requires a bit of feel on both setting the gage and measuring it with the O.D. mic. It's true a dial bore gage would be more accurate. Also next time, if you did'nt this time, take several measurements to see if you get the same thing everytime.

Just my 2 cents....