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I've got an 66mm Asso piston knocking around in the shed from a few years ago when I had a 200 rapido. Anyway rather than splashing out on a new piston to carry as a spare, any recommendations for someone to cut/alter this piston? Its to go in a GT200 big block kit so need it altering to suit a reed kit I am assuming this will fit as well crown height etc. I just want one spare "just in case". Appreciate your help

I fully understand your question & an expert will be along shortly, concerning the GT kit. I seem to recall Dimitrios posting on here some images...

However, if the piston is purely as a back-up, it will run anyway, regardless of cutouts, surely?

That way, if not put into use in the scenario you describe, it could serve elsewhere.

Just saying....

Aaah I see to be honest this is my first time with a reed kit , always been piston ported prior to this, iron barrels, and various rapido's, so wasn't sure if a "normal" piston would work.Basically its my back up piston for the Euro, so with a healthy sense of paranoia I'm trying to cover all bases. So it would work then as is without being cut?

It would run. You could perhaps try it to convince yourself prior to your trip for peace of mind...

I am aware that many tuners seek completely 360° inlet timing with reed valve inlet ports into the barrel, but that is a 'swings & roundabouts' scenario in which any ultimate power can be offset by the loss of reliability/increased wear due to lack of piston strength & exasperated 'rocking' of the piston in the bore.

My comments are only intended to help

The GT kit i believe uses a Yamaha piston so the crown height as well as the dome height is different to the Asso

Unread postby dscscotty » Tue Jan 10, 2017 6:10 pm

The GT kit i believe uses a Yamaha piston so the crown height as well as the dome height is different to the Asso

You are quite correct & I apologize for missing the obvious!

I think the ('central') compression height is 36 mm as opposed to 39 mm...

Warkton Tornado No.1 wrote:

Unread postby dscscotty » Tue Jan 10, 2017 6:10 pm

The GT kit i believe uses a Yamaha piston so the crown height as well as the dome height is different to the Asso

You are quite correct & I apologize for missing the obvious!

I think the ('central') compression height is 36 mm as opposed to 39 mm...

I concur.
You could of course carry a 3mm base packer with this Asso and hope you have sufficient adjustment to re-fit the exhaust and cowlings.
Change the piston back to a Yam one when you get home though cos those Asso's don't last.
Might just be easier to fork out the £50 or so for a spare Mitaka though?