mocking up tomos top end with puch piston.

Hopefully soon this will be my first attempt at top end modifications.

Squish: Piston was initially dead even, but I put a spacer in there and it measures just shy of 1mm squish. Figure this will be okay with a stock head.


After buying and breaking piston rings for a different airsal piston I just threw the puch piston in it. It seems to be a really good fit but might be a little loose in there. ...(I know what I did wrong with the rings. I forgot to file the gap a little. they were on there but couldn't get it into the jug. was impatient....)

At TDC you can also see the piston flaps stick out a little into the intake. Assuming I should cut that back. Any advice here?


At BDC it looks really good and have a good gap to widen the exhaust port. Transfer ports match up perfect.


I will probably just try to get it running first before I start drilling stuff out but still want to post this.

Questions/ concerns.

1.) Piston intake window.... Wouldn't air be pushed out the window during the compression cycle also? .. I guess that is what reeds are for? Basically, should I put a window? Any design recommendations?

2.) Anything else I should consider doing? I don't want to do anything crazy just yet but is there any other basic things I should think about when it comes to cylinder modification. Will this (puch piston, etc.) even work

Eventually I will get into the transfer ports

Re: mocking up tomos top end with puch piston.

theres good info on tomos porting in the wiki.

Re: mocking up tomos top end with puch piston.

EH 📣FCC of the QCB /

That looks to be one of the “faster” stock Tomos kits. Those intakes save a lot of porting time. Notch the piston skirt where it does not clear and cut a window in the piston and it should be good.

Re: mocking up tomos top end with puch piston.

that little bit of cover up on the top isn't going to make much difference but you definitely want to cut a big window or 2 windows into the piston

you'll get more mileage out of porting the intake hole further down towards the crankcase, but windows in the piston will make it a 360 deg intake no matter what

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