24 stud crankshaft in a 21 stud engine

[Russ/40]

Originally Posted by flatheadmurre

Have you testfitted them in the block yet ?
Hopefully you don´t even need to machine the full 1/16...
Any shop with a CNC Lathe around ?...then you can machine the pistons...maybe easier then machining the heads.

First: I am currently half way through another build, so although I have the block and rotating assembly for the build ( less the rods ) we are discussing, I havent even cleaned the block yet. I am in the theoretical stage as to the pop-up motor.

I know cutting the pistons would be the easy way to go, but i'm thinking there could be some performance gain with the pop-up approach although it probably be minimal. I can sculpt the combustion chamber for good squish, and maybe better flow. Certainly this has been done before. I think Navarro had heads for this. Which tells me there had to be a reason for doing it.

Gary, the pistons I have that are .125" over are Egge's EP-1091 which spec the CH as 1.625" thus the interest in a pop-up piston configuration. Also, the deck has never been cut, and I usually don't unless absolutely necessary. I have 21A rods, but they all need to be worked, and I know their lengths are all over the place as they are.

Thinking out loud, as this is the one engine I have wanted to do, have never attempted before, and will probably never do again, if I do it. Clearly i need the benefit of experienced advice. I appreciate all the help thus far.