commando engine - clearance piston to cylinder head

[robodhran]

Rebuilding my 67 273cui commando engine.

I am using RaceTec HiPo pistons with dome and have a commetic 3-layer metal head gasket with .040" thickness. Everything very good quality.

The fact sheet of the pistons says, that the RaceTec high compression pistons should have a minimum static clearance between piston and cylinder head of no less than .040".

The piston sticks out the block deck exactly .004" at the rim at T.D.C..
With the .040" gasket, that will make a clearance of only .036" (.004" less than minimum).

Does anyone have experience with these clearances? Will this work or will I have to consider to change to a thicker gasket? Any recommendations? Don't wont to work on the pistons.

Checked valve and spark plug clearance as well --> it's ok!

On the pics you see the piston sticking out the block deck (rim). The black spot you see is modelling clay that I first used without and the with the gasket. But this is no reference, since I did not tighten the gasket.

Robert

 

[robodhran]

...b.t.w. - we have 98-100 oktan roz fuel here in Switzerland...helps with high compression engines....

 

[perfacar]

hi, the original 235/273 had .011 down at edge, they had steel shim gasket, measured .016 , I've ran my 273 with this setup. gives you .027 total even with .020 gasket comes to .031 total. just food for thought. might consider a thicker gasket?

 

[RustyRatRod]

.036" between the piston and head is fine.

 

[famous bob]

.036" between the piston and head is fine.

agree w/ the last post. got .036-.039 om my 505. steel rods only tho!

 

[69 Cuda 440]

Piston-to-Cylinder Head Clearance

.035" is as close as you want to go, if you're intending to hit 7000 RPM's.

Race-Tec Pistons are excellent units.

With a 'Zero Deck', we use .041" Head Gaskets.

 

[nm9stheham]

.035" is a common minimum found around in various applications data.

What cylinder to bore clearance are you running?

 

[robodhran]

Cylinder to bore clearance is .008 mm --> 0.0031"

I decide to stay on the save side and will go for a .051" cometic MLS head gasket. This will provide a clearance of 0.047" (1.19 mm).

So maybe I'll put my .040" cometic MLS gasket on for sale on the "parts for sale threads", as soon as I receive the new gasket.

The .040 has not been compressed (just put on the block to see if it fits...). It has the exact bore diameter for (3.700" for 273 engines) and has 3 layers.

Robert

 

[mguner]

Safe is good.