Cutting intake window in genuine Polaris Piston for 2PG

[JeffHWV]

I am re-rebuilding an 88 Marathon after losing a piston due to lean condition. I bought a genuine Polaris/Robin Piston and rings along with a NOS genuine Mikuni bv24 carb that hopefully prevents the lean issues caused by the Chinese Mokini junk carbs which I can never get the needle and seat to work dependably. The engine is a fairly low hour complete overhaul by me a couple years ago including 3 new SKF bearings. I am also replacing the cheap aftermarket crank seals with Victor Ford Contour cam seals. I have the two old pistons from the last overhaul and this time and they are both aftermarket. They have two different size and shaped windows. One is bigger and very square and the other is smaller and has rounder corners. Does anyone know what the original specs or measurements for the window should be or is there any way to optimize the window placement? Any insights on window size as far as charge flow amount versus velocity and what effect it has in overall power versus low end torque? I would think having sharp corners could lead to cracking. Thanks.

[cart around]

I was able to copy, but don't know how to post the link with my phone. There was a guy named restore49 that did the same thing. He put the port in the same place, but thought lowering 2 mm might help.

If I figure this out, I will post the link.

https://www.buggiesgonewild.com/showthread.php?t=119891

I will add one more thing. I'm an aircraft mechanic that does a lot of structural work. Sharp corners are bad. We round off any and all corners. I would look at matching the shape of the intake port.

[JeffHWV]

Thanks for the reply. I think that may be the thread where I originally got the idea. I couldn’t find it before but read a couple of similar ones. I’m thinking about putting it together dry and stuffing something in the port to mark the piston. That would give me the lateral boundary. Then I’d have to figure out the up and down.