Piston Identification

[ULARARA26]

Hey guys,
do genuine oversize pistons have any markings on the piston crown to indicate what size they are, l am able to see the tops of the pistons with camera down the spark plug hole, l can see the numbers, just trying to ascertain whether l'm looking at the original pistons or those from a first or second overbore. ? Its an xs2 with supposedly 22,000 miles on it, runs good, no smoke, and no lip at the top of the bore l can detect. with that sort of mileage and going by the cosmetics l'm guessing its had a bit of a hard life, so suspicious it may have at least the first oversize pistons fitted and a rebore at some stage.

 

[Wingedwheel]

Not every rebuild require OS pistons. Most times a re-ring will take care of it. How’s the compression?

 

[jpdevol]

do genuine oversize pistons have any markings on the piston crown to indicate what size they are

An OEM std bore piston would have a 3 digit number designating its fractional diameter vs 75mm: 954 = 74.954mm, 962 =74.962mm

An oversize piston would be stamped with its overbore diameter: .25 =75.25mm, .50 = 75.50

 

[ULARARA26]

Not every rebuild require OS pistons. Most times a re-ring will take care of it. How’s the compression?

Compression is good, getting approx 130 cold on both cylinders and low to mid 140's on a warm motor, which made be suspicious it may have had a rebuild, or l'm just fortunate.

 

[ULARARA26]

An OEM std bore piston would have a 3 digit number designating its fractional diameter vs 75mm: 954 = 74.954mm, 962 =74.962mm

An oversize piston would be stamped with its overbore diameter: .25 =75.25mm, .50 = 75.50

Many thanks, will have a closer look at the numbers.