piston crown height

[‘AAA Dummy]

Hello, I need to check the crown height on various pistons that I am playing with at the moment , question : is the measurement taken from the center of the gudgeon pin or the top of the hole in the piston. I assume there will be a standard way the measurement is taken . Thanks for any help on this

[Brian]

Hi John

A look at the Polaris site may help. Polaris do loads of two stroke engines for snowmobiles, outboards etc and I believe they list them all somewhere with tech specs. You may find a suitable piston for a project or find out the industry standard for measurements.

[Derek Reynolds]

I would plump for the centre of the gudgeon pin, but the key element is surely the proximity to the cylinder head and the gap remaining between the two which will ultimately determine the compression ratio. But perhaps that is an answer to an unasked question?!

[‘AAA Dummy]

Thank you guys for your replies , having asked around the trade I am going with the center of the pin. My problem is that not all suppliers quote the crown height and the ones that do don’t say where they take the measurement from. Some will just ask
what machine is it for, In my case this is no good as I am looking for a pair of pistons to fit an Adler MB250 twin that I am rebuilding, It will have Kawasaki KX125 motocross conn rods. All good fun While in lockdown.
Regard John

[William Dunstan]

most crown heights are measured from the top of the gudgeon pin hole ( check the Matika pistons sight though the do not list MZs ) . This seems to be what is used by most manufacturers , but I have seen tuning manuals where my have measured from the centre of the pin.
hope this is helpful.
Big Bill ( Dunstan )

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