Building a 372XP Big Bore With 272XP Piston

[nmurph]

So, what's your take on any of the AM BB 372 kits? Can they be made to run as well or better than OEM?

 

[Mastermind]

Oh yeah.......the one's I've seen have been very nice. But the damn pistons........I worry about them not holding up.

 

[Rudolf73]

This one time I made a piston out of a bit of hardwood, it worked, sort of...

 

[jd548esco]

i wonder if anybody has tried a slab piston in a saw that had a windowed piston??

i wonder how would that do??? -- LOL

 

[KG441c]

Here's a few pics......I'll be adding to this one.

Opened up the transfer inlets a bit since the 272XP piston is a windowed design.





Here we are test fitting to the case. The match is worse than you can see here.....



Here it is after being case matched.......



Like I said......I'll post more as I set the squish and port it.

Randy will the amount u took from the cylinder and crankcase matching affect crankcase compression much? Increse rpm ?

 

[KG441c]

Randy will the amount u took from the cylinder and crankcase matching affect crankcase compression much? Increse rpm ?

Sorry I saw your comment on the case compression after reading the whole thread

 

[Huskybill]

I seen a 2100 cylinder that was ported by a husky salesman I think he got his info from husky. He raised the exhaust port 1/8” in the center and arch it to the sides by 1/16”. He lowered the intake port by 1/8”. He opened up the transfer ports. He cut 1/8” off the bottom of the piston and I advanced the timing. The 2100 was a beast. We plugged the govenor.

I followed his lead on a 81/250cr husky motocross bike, I did more porting. And advanced the timing. This bike was unbeaten down the straights. She was an animal. With the cylinders that had ribs in the transfer ports I thinned them, lowered them and put a c shape in the middle to keep the flow centralized.

 

[MG porting]

Here's a few pics......I'll be adding to this one.

Opened up the transfer inlets a bit since the 272XP piston is a windowed design.





Here we are test fitting to the case. The match is worse than you can see here.....



Here it is after being case matched.......



Like I said......I'll post more as I set the squish and port it.

That 272 piston look right at home in that cylinder. Good work Mastermind.