268 piston for 372xp

[Nitris223]

Which piston would you guys use for a 372 xp. I'm doing a little experimenting with a AM cylinder before I use the new OEM cylinder I have.
These pistons came with the saw that was a xtorq now being converted to a 372xp OE.
The windowed piston on the left looks nicely made and the rings have a small HW on them, it was just in a small ziploc bag. Maybe hyway rings.
The slab side piston was in a Farmertec box. Slightly lighter piston also .
I know which ever one I use will need to be machined into a pop up depending on the squish clearance which I have a lathe for that.
I do have a couple Caber rings also.

Still waiting for my right angle hand piece to get here before I can do any port work.

I searched the forums quite a bit and I can't seem to get a solid answer if guys are still cutting down the cylinder wall flush with the base or not. It seems to be 50/50.

Also are the upper transfer ports and 2 different heights. Looks like the port closest to the intake is higher then the rear port. Maybe a degree or 2. Haven't checked with the timing wheel yet. I don't have my OEM cylinder yet to verify if they are the same. . Waiting for a buddy to pick it up for me in a couple weeks.

The AM cylinder I have I checked the timing a while ago and it is
IN 75
EX 102
TR 125
SQ .20 NBG.

My plan is to set the squish with a base gasket to the stock 2 rink piston then machine the 268 piston to work.

This way if I don't like it I can always go back to the stock piston and still have good compression.

 

[huskihl]

I would use a 372 piston in a 372

 

[Nitris223]

I would use a 372 piston in a 372

Why not use one of the 268 50mm single ring pistons vs the double ring 372 piston. Just curious on your reason.
From the what I have found to read about it, there doesn't seem to be anything detrimental about it.

Like I mentioned in my post , it will be set to work with the stock piston first then the pop up cut on the 268 piston to the same squish.
The saw is blown up and getting a complete rebuild so I figured while the pistons are there I would see what people's thoughts would be.

 

[huskihl]

Mostly, because pop-ups shoot the charge uphill where it can mix with spent exhaust and be carried out and be wasted. The bottom full skirt on the 372 piston also serves as a ledge to push the charge up through the transfers in my eyes. And on top of that they just work.

 

[RedneckChainsawRepair]

Why not use the early 1 ring 371 372 piston if worried about that.

I had a hot 372 with 372 piston if I recall right had windows put in it by porter.

 

[NSEric]

I'd use the piston out of the 268 open port cylinder.
It's solid on the sides like the 372 piston with no windows but has one ring and is taller just like the windowed 268 piston.
It's to go to 372 piston for guys who cant machine cylinders. You can grind it down until it fits and you have good squish/compression.

 

[RedneckChainsawRepair]

This old 372 race saw in a 52mm used a stihl windowed piston too. Back before you could just buy a wiseco to use like today.
Was one that was stroked 2mm too to fit the 81cc limit 5ci class too. Mine wasnt stroked.