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1G Decking a Block. Piston Protrusion

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SasaniFab

Proven Member
2,433
782
Dec 1, 2013
Mexico, Connecticut
Ok ...so many of you guys have decked your block. This is the first time ive experienced this issue. After assembling the shortblock I noticed at Tdc the pistons protruding a thousand of two out of the bore. I placed a used oem mls headgasket on the deck and the piston sits a few thousands below the top surface of the headgasket. We are using bc 270 cams with stock cam gears. At what point is the block junk
 
I'd venture to guess the block is too far gone at this point but it all depends on what pistons your running. Do you know how far the block has been decked total. Service limit on the head is .008 usually the most you can get away with before running into issues is .020

To know for sure you'd have to do a clay test or better yet do a dynamic valve clearance test. You should have I believe .100 thousandths clearance to be safe. If your not too far off you could fly cut the pistons so you could still use the block
 
Just measure the ptv clearance and piston to head. Our engines have horrible quench anyways so it won't hurt anything as long as theres adequate clearance.
 
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Yeah, 2nd piston to valve measurement. Gotta get an accurate measurement of protrusion and check PTV. Worse comes to worse you fly cut the pistons. And yeah, also measure your piston to cylinder head. But a thou or two shouldn't be awful. Fly cut the Pistons and possibly a thicker head gasket. I don't think the blocks junk by any stretch.
 
You need to measure the piston to head and valve to piston clearance and get a headgasket to get the proper clearance.

Many engines are built that way stock with the pistons above the deck.

As mentioned above, if it’s an issue getting another gasket you can just cut the tops of the pistons down.
 
Well he gave me a hks 1.2mm head gasket, I told him to exchange it for a 1.6mm or 0.062, should give us some better clearance
 
Yes JE mirrors the combustion chamber, and 8.5:1. I think that's about right for my application. I have to much exhaust pressure to get a gain in ve from lower compression. Regardless of the quench doing anything it does reduce the chamber area for a given compression, and improves the heat release rate. I think I'm still in the area where I don't need to slow it down to keep peak cylinder pressure down. It's living with pretty close to mbt timing on a $25 felpro and 40+psi.
 
Yeah people don’t know about the ve thing.

When you’re “sucking” air swept volume is displacement. When you’re blowing it in, with higher intake pressure than exhaust, the dish and head chamber displacement is filled too.
 
I've been shooting for 0.030 piston to head clearance lately. Helps quench.
Very interesting!
I’ve always been curious about achieving optimum quench.
Can I ask you a couple questions?
1) What compressed head gasket thickness do you typically run?
2) How many thou negative deck clearance do you typically shoot for on your engine builds?
 
I have the head and deck cut for MLS. I also use vigrin heads and try not to cut them much. Old heads get soft and flex. I use old old standard ARP torqued to 105ft*lbs. The timing is close to mbt, but probably 2-3 soft.

Now it's not fool proof, over a season it starts to push a little coolant. But if there's a problem it knocks the gasket out and it tells me something is wrong, where a MLS let's it keep on till you torch the head or kick a rod out.

I'll get backlash, but a MLS does not seal, better. They are just stronger and stay in place better. Less of a fuse.
 
The mls will seal higher combustion pressures, but the composite is fine for most.

I have a block out there that seals up 60+ psi and a 150 shot. We went back to mls from a composite and dual o rings. The next setup will be copper gasket and o ring/receiver.
 
How many of you guys are running the hks, this has been my go 2 gasket for all of my motors lately. Ive had 0 issues since I started using them. My current setup sees 40+ psi on e85. Im aware that 40 psi isnt anything magical.
 
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