Piston/Cylinder measurements

[Chino886]

How can you tell if the piston/cylinder combo are within tolerances? What measurements can you take? Please help, I have a used piston and cylinder that I want to know if they are any good. If not, i will just bore the cylinder out....

Thanks in advance...

[wilkin250r]

Sweet, an actual technical question!!!

It's the kind of measurement that, in order to do properly, requires some specialty equipment. But you might be able to get away without it.

Absolutely necessary is a proper bore gauge. It can be the type that takes the measurements directly, or it simply snaps to the bore diameter and then is measured with a separate gauge. A good measurement device is also a must. A micrometer is best, but you can probably get away with a good set of calipers.

It helps to have a calibrated granite block and stand, to determine if the bore is straight and perpendicular to the head and base. Measurements are taken at the top (about 1/2 down from the deck), at the middle, and bottom. One measurement from front to back, another from side to side. Six measurements in all.

Generally, measurements for the piston are taken at the bottom of the piston skirt, directly across in the direction of of intake and exhaust (front to back). This is because, believe it or not, pistons are not exactly round. When they heat up, they expand more side-to-side than they do front-to-back. So piston manufacturers make this dimension smaller to prevent seizure.

The crown of the piston also heats up and expands more than the skirt, so pistons are actually smaller on top, and wider at the bottom.

This may be a little more complex than you wanted to get into. If it's a little daunting, just send the combo to your local shop, I bet they'd do the measurements for less than $20.

[Chino886]

Alright Wilkin,

Now lets try again in English, I didn't know that you knew I was Asian, but I did not understand that.......:D

I will probably take it to my Honda dealer or a local builder around here....hell, I would probably spend more in tools....

Or, Plan B, I'll just send it you you for free...:devil:

Thanks for the reply.....just the information that I was looking for....

Chino...