Piston Cut for reed valve

[DaveTomo]

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

[Warkton Tornado No.1]

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....

[DaveTomo]

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?

[Warkton Tornado No.1]

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

[dscscotty]

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

[Warkton Tornado No.1]

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...

[Fast n Furious]

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?