12 valve piston pertrusion

C

cumminslow

New member
i am finishing my spare engine and ran into a little problem .i have a 96 block that has been decked 7 thou ,i installed a set of marine pistons and my piston pertrusion is anywhere from 34 to 39 thousands i know i can get away with a 20 over gasket or get the pistons cut down to about 27 thousands,what have you guys done in the past or has anyone ran into this i would like to hear opinions thanks .:Cheer:
 
your best bet is to shave the pistons down your head gasket at 20 thou over in my eyes is a weak point but then again if it is not going to be a high hp build then you would be fine with the gasket. i like the stock size gaskets bc i know they work and its less to worry about for me!! hope that helps good luck!!!
 
First gen and industrial pistons have two different heights cyl 1+6 are higher than 2-3-4-5
 
I would machine the tops of them down to what you need. And run a standard gasket. This happens ever time i do a motor. Nothing out of the ordinary.
 
machining the top is 1 option , i also realised that the back of the piston is taller than the front by about 4 to 5 thou i dont know if this is the way mahle makes them or what ,also on commins pistons is the same way 3 to 4 thow front of the piston is lower than the back ,i took masurements from the top of the wrist pin so iknow that is not moving that much
 
How are you measuring this? Are you sure the skirt isnt casted different?
 
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Take the piston out, turn it around, and measure it again. Last one I had with that problem it turned out to be a bent rod.
 
dial indicator of the block i set the dial indicator on the block and check each piston front and back i did check a different block that has the head off and i have the same results front of the piston sits about 3 to 4 thou lower than the back i dont know if any of you guys ran into this issue maybe it supose to be these way ,maybe the piston runs hotter in the combustion camber wich is closer to front of piston and it gives room to expand just thinking what could it be
 
if i have a rod issue it means that all 6 are bent ,plus they were at the machine shop for new bushings ballancing stress relief and shot peen ,you figure they will catch a bent rod
 
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