shrinking pistons?

[jason frost]

it was checked by the reborers at rebore time then i believe by the man who tuned it then by my very experienced engine builder at first build then after a few problems we couldnt understand was checked again in front of me .

How did he measure it ?

[Donnie]

That's the question.

Has it been measured in the same way all times, ie I've seem people measure it with the piston skirt to spigot, piston crown to spigot, piston skirt to cylinder head end and piston crown to cylinder head end!

Only one of these is right!

[Lambretta Sash]

I'm intrigued, but ponder on the following

A misaligned con rod does not let the piston rings have proper contact with the cylinder wall allowing pistons to wear rapidly and unevenly ?

Or inlet port shape can cause rapid wear ?

Hope this helps

[mark]

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

[mark]

The crank is true and the rod is straight both have been tested. The piston is not worn,just physically smaller in size than it was when new, I know this is not unheard of in the bike world as well I just wondered if anyone had it happen in scootering and judging by the comments on here and other forums and pm,s I have reicieved it's not uncommon with this type of piston sadly.

[Supereibar]

this throws every concept I have been studying about two strokes out of the window... Am I hopeless?

[willwander]

That's the question.

Has it been measured in the same way all times.....

[soullad]

Aside from yours Mark, I've seen 2 pistons that show this. Characterised by darkened blow- by almost all the way round the piston. I cannot recall if the ring gaps had altered thou. I know others have seen this and for very understandable reasons prefer to sort it out privately.
On a general discussion type basis, could differing levels of silica content cause this?

[mark]

i just wondered if anyone else had heard of it ian, it seems that others have and have kept quiet about it in fear of upsetting certain dealers . that is something i dont underrstand to be honest .
if this is a common problem as it seems to be are these pistons fit for use as in the sale of goods act ? .
i applaud new products as long as if there is a problem batch the dealer or dealers concened stand up and say.
i contacted the dealer about this yesterday and was told as i didnt personally purchase this part(my engine builder did) its up to him to take it with the dealer and they wouldnt/couldnt discuss it further with me which is fair enough

[dirtyhandslopez]

The water that's in them to make 'em lighter has evaporated :biggrin:
Too much filler, not enough meat
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