Yamaha 2003 LS2000 LST 1200B piston

[gonzaloak]

Hi, one piston of my 2003 Yamaha LS2000 is damaged and needs to be replaced, but have been looking at Yamahapartshouse.com and they show 3 different type of pistons, Piston (0.25Mm O/S) AP , Piston (0.50Mm O/S) AP and Piston (Std) UR STD. On the other hand, at partzilla.com, there seems to be only 1 piston spec; Piston (0.50Mm O/S) AP.
Looked at the damaged part, but cannot identify which one is the proper one for the engine. Will appreciate if someone can give me some guidance.

 

[gt5pilot]

Measure the bore of the cylinder and compare it to the stock spec to see what size it is. The .25 & .50 are oversize that require machining of the cylinder.

Is the cylinder damaged? Will it need to be machined to get it cleaned up so the new rings will seat properly?

 

[gonzaloak]

Thanks.
Cylinder looks fine, just small scratches, but nothing in particular. Will polish it and measure the resulting bore. By the way, should I look to change the 3 pistons at the same time to avoid the motor running bumpy? The other 2 pistons are working fine and good compression, but surely have some minor normal wear, after all, are the original ones from 2003.

 

[the MfM]

The top of the pistons should have markings indicating if they are oversized or original.

I would reuse the pistons if they are in good shape but while you have it apart I’d suggest replacing all the rings.

Remember there is a front and back side to the piston!