Hi from Germany!
Maybe someone can help me out.
I have a Gen6 502 MPI wich is fully apart on my bench right now.
The piston skirts are scratched a little bit, so i decided to measure all the cylinders and the pistons.
I have found that the cylinder walls look super clean and have measured them at 4.4615. Due to inspection error i think they have the original 4.466.
Out of round is between 0 and 0.001.
I have decided to just hone them and get a set of pistons. The pistons i have, are (i i have no errors in measurement) at 4.4150 what would be a piston to wall clearence at 0.051 !
I Think the service piston to wall clearence is max at 0.0065 !
I don`t know whats wrong with that pistons but the cylinders are super nice!
What kind of pistons do i need to just refresh with the original bore?

Thanks in advance!
Philipp

You need to re-measure everything again, probably miss reading the mic but That’s not something you want to guess at.

JE and SRP both have standard pistons that are 4.470" bore for 502's. They just need a good hone of about .003 and are ready to go. That is pretty much the standard for a stock rebuild on a 502 and typically jumps up to 4.500" from there

Is it normal for the pistons that the skirt is much bigger than the top of the piston?

I Re-Measure and check it again.

You need to re-measure everything again, probably miss reading the mic but That’s not something you want to guess at.

The JE/SRP route is the way to go because you'll be able to use more commonly available rings - the Gen VI ring pack is hard to find and is very expensive.

Bite the bullet and bore the block to 4.500 and finish hone to JE's recommended piston to wall clearance. Make sure to balance the rotating assembly - you'll be surprised with how smooth it runs after. The factory balance is so/so.

Yes. Crown gets much hotter than the skirt and they serve different functions.

Did you measure at the spot the piston manufacturer tells you to ? You need to. Pistons aren’t round and not same size top to bottom.

No i did just measure at the middle of the skirt. Where should i measure with original pistons?

Usually je are measured 1/2" up the skirt from the bottom

I saw the same, but Def call
JE as you want to be in exact spot designed for it.
Call: (714) 898-9763
They are in California.


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