A piston question from a trials/non-scooter guy

[d2w]

Hello,

I hope this is the correct sub-forum to post this question.

I'm the mechanic for my son's 2007 Gas Gas TXT 70 trials bike. The engine is kind of a one-off in that it was made by Franco Morini. The engine is 72cc (47mm x 40mm stroke) liquid cooled with a hydraulic clutch. I believe the engine derived from the Franco Morini MC65. The cylinder is an iron bore unit from Metrakit. I could not ID the piston.

I am hoping to over-bore the cylinder to 80cc (50mm x 40mm stroke). One piston which "looks" reasonable is the Polini 204.0829A. This piston is compatible with something called a "Derbi Senda", and when cylinder kits were available for that bike (Italkit used to make the CK.22.750.g) they were noted as being compatible with the Derbi Senda. Hence my "compatible by association" theory.

Can anyone suggest how I might be able to obtain detailed specs for the Polini piston? I would need to verify ring pin positions, piston pin to edge measure, dome height, etc. I've written to Polini in Italy but have heard nothing back so far.

Does anyone have a piston from a Derbi Senda which can be measured?

Can you suggest another forum/sub-forum I should try my query (not being part of the scooter crowd)?

Your suggestions as to how to find a compatible piston for this bike will be greatly appreciated.

Thank you.

Dale

[pinkscoot]

Try seeing if the seller will measure it for you.

[190mech]

There is a Derbi Senda listed in this piston dimension chart;
www.mitaka.co.uk/CATALOGUE/PISTON_DIMS_ALL.htm

[ThomasTPFL]

Where are you? Every chance it is the same engine as I know in scooters at least Derbi used Morini engines for a while.

If you're in the US I'd suggest shooting an email to Dos Cycles in Atlanta. Their website is devoted mainly to mopeds but the guys that run the place are equally knowledgeable on small shifties.

[ThaiGyro]

My additional question...if I'm not mistaken your piston pin is a 12mm? If so, there are many parts I have seen in the past based on Morini cylinders. Mostly verticals from my world. Many Honda and Peugeot bottom ends were 40mm stroked, with 12mm pins.