Hello All,
Need some advice from the engine gurus.
Am moving along on my 270 rebuild project. This is for my GMC CCKW 2 1/2 ton truck. Stock engine configuration, no hop-ups. Engine was just bored 0.030" over (up from an arsenal rebuild of 0.020") to clean up the cyl. walls.
Provided my machinist with the pistons that I plan I using. They are NOS, but I am unsure of the brand as I purchased them second hand. They are definitely cast, not the heavy Zollner forged like ones that the military uses. Full skirt, three 1/8" rings, and one 3/16" oil control ring.
Machinist said that pistons were uniform in diameter, so he sized all bores with 0.002" clearance.
I double checked all measurements and found that there is almost 0.001" variation among the pistons (as measured at the bottom of the skirt - perpendicular to the wrist pin axis). There is also about 0.0005" variation in cylinder diameters.
So theoretically, I could end up with a cylinder with just under 0.001" piston to wall clearance.
Army TM specifies min. 0.0035", and even provides a separate warning about never going below this value.
I realize I am not running the OEM forged pistons, but 0.001" - 0.002" seems a little tight to me. Am thinking about taking the block back, and having him open up the bores another 0.0015 to 0.0020"
What do you guys think?
What piston to wall clearance do you typically run on these engines?
Thx in advance for any help that you can provide!
