Im doing the preassembly of a 91 350ci .060 over, KB193, without the piston rings. https://www.thirdgen.org/forums/atta...7896.306ko.jpg

Piston to deck is .003 to .005, on the sides over the wrist pin.

At the same time by rocking the piston back and forth, the combustion chamber side never gets over the deck, but it can exceed up to .008 over deck on the squish side of some pistons.

I know operation themperatures will reduce the clearence, but how does .008 over the cold block deck sound? I plan to use the FP 0.041 head gasket.

Thanks.

 

Ill give you a example Im doing a 406 for mine and the block has been race preped. the block is 30 over but the pistons are set to be without the rings 4.15075 +/- 0.00025 inches (thats on a 4.155 bore on the block) put the rings in and check it again. You should be good once you install the rings but check it after to make sure.

 

Sure, will mesure with the rings too.

How much do your pistons rock up and down at the squish side on the "edge/outer side of the piston" ?

 

Nobody ever mesured piston rock during pre-assembly?

 

Nope

Piston to cylinder wall gap is measured with a very long feeler gauge down to the skirts. If you have the proper feeler gauges and the clearance calls for .006", the feeler gauge will go down the length of the piston, past the rocking point of the wrist pin. With the feeler gauge above and below the pivot point, the piston won't rock.

Once the rings are installed, the piston won't rock and you can't check the cylinder wall clearance. The piston to cylinder wall gap depends on what the pistons require. Cast, forged and hypereutectic all require different clearances. Forged pistons are sloppy compared to cast because of how much they expand when they get hot.

 

Thanks alot for the information.

Unfortunately I only have standard feeler gauges.

The bores are .060 overbore, I did check them, all are out of round, #4 .0016", #1 .0008" and the rest of them .0012 in. (giving .060 + .001X out of round, across the bigger oval diameter)
Service manual, Engine specifications list, production out of round .001" and service .002".

I did not mesure the piston skirt diameter, I supposed they are machined to have the proper clearence to match the selected overbore.

KB193 hypereutectic, street & towing Suggested Piston To Wall Clearance is .0015" - .0020".

I will mesure the pistons and look for a long feeler gauge.

 

Turns out piston to bore clearence is correct within specs.

It still sticks up 0.008"-0.010" over the deck on the squish side outer edge by pressing down the piston at the combustion chamber side, with the rings installed.

I plan to use the FP-1003 0.041" head gaskets.

Quench distance over the wrist pins is 0.003"-0.006" under the deck.

Should I go ahead or look for a thicker head gasket?

 

to be extra sure use some molding clay or playdoh to check it with the heads on but I think you should be okay.

 

I did use molding clay to verify piston to valves clearence.
It had around 0.055"-0.060" thick clay on the quench side, thoug the head bolts were only torqued to 45 lb.ft.

Maybe I am getting too carried away with the piston rock, it could already be included in the "nominal" safe 0.040in piston to head clearece mesured over the wrist pin.