Scooterotica

Surely if the pistons are wearing excessively there has to be mechanical interference between the bore and the piston? Wouldn’t that bring the fuel/oil ratio into question?

ok
I will run it by our metallurgists and see if they have any thoughts.

mark wrote:I have asked what tools were called that were used and I can now say
Piston measured with external micrometer, bore with a bore comparator

Nice one same as me

the piston IS NOT WORN

Roger mother bird

eden wrote:how Ive understood it, they aren't waring away, they are apparently physically shrinking

From what has been said so far it would seem so, but without knowing all the sizes of the piston before it was fitted shrinking is an odd thing to say to me. Top to bottom, side to side would all be different and thats not a thing I would check before fitting, you would need to know the size of the piston at all these points first then check them again to say the whole piston had physically shrunk or am I missing something ?

Could we interest these pistons in a wafer thin mint?

its quite simple really
A : the engine was built with 4 thou of clearance of piston to bore

B: it ran for 500 miles approx and got exceedingly hot the more miles done ,no distance was more than 25 miles at any time.

C: when stripped to find problem piston to bore clearance was 6.5 thou, which is 2.5 thou more than it was when measured in the same position

D: the bore and the ring gap are IDENTICAL to the original build and the piston is not

to me and my engine builder this equals a piston that has shrunk, it is a piston no more it is dead.

do you have another explanation for this pheonoman ?

Answer has already been aluded to Mark. It's the silicone content.
Think about it, when you caulk a window with silicone, after a while(granted, years) the silicone will start to shrink and you have to do it again.
In an engine the heat factor is a lot more than on a window, therefore the deteriation will happen far more quickly.
What may have happened is that there was a bad batch of pistons made with too much silicone in them. Great for not seizing and or a race meet, but no good for a road scoot. Everything is a trade off.

that is exactly what the metallurgist i spoke to today said , he said he may be able to test the piston when he gets back from his holidays