Oversize Piston Required ?

[neashfella]

I have a 2001 sherco 2.9 and the engine seems a little noisy so i have taken the top end down to check piston. Unfortunately i do not have micrometer and internal to measure bore and piston but without rings on i can get a 0.1mm feeler gauge snugly between liner and piston - does this mean there is too much play and an oversize piston is needed.

Also would really like some advise on how to check main and big end bearings if possible.

Thanks guys !

[charliechitlins]

You can't do it with a feeler gauge like that.

And, your piston is cam ground (oval)so it makes a difference if you measure fore and aft or by the wristpin hole.

BTW, a piston is smallest side-to-side by the wristpin (gudgeon pin).

What you can do is put a piston ring about 1" up from the bottom of the cylinder, square it up by pushing it in with the piston, and measure the end gap.

There will be very little wear there because the rings don't go down that far.

It will be close to standard bore.

Then push the ring to the middle of the cylinder and check the end gap.

Do this in a few places.

Now...this will show you the change in circumfrence.

In order to translate that to the change in diameter, you have to remember your High School Geometry and divide by pi.

As for the crank, you need to get the spec for endplay (side-to-side), and make sure there is no up-and-down play in the crank or the connecting rod.

Don't worry about side-to-side play in the rod. If your unfamiliar with this, it may seem grave, but it's standard.