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Discussion Starter · #1 ·
I have to replace one of my head gaskets and was wondering if the lifter pre-load adjustment is different from a hydraulic flat tappet engine. I have the OEM roller lifter cam in my engine (GM crate motor).

In the past I have always used a 3/4 turn on GM small blocks with hydraulic flat tappet lifters. I just want to make sure that I get it right.

Thanks,

Hans
 

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Discussion Starter · #3 ·
It is a zz 454 HO GM crate engine with the optional GM aluminum heads with oval ports. I don't know if that would be a gen VI engine. It has the aluminum cast timing chain cover but also a mechanical fuel pump.

You say there may not be an adjustment......are the rocker arms shaft mounted like a mopar engine?
 

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According to the GMPP catalog, this block is a Mark IV/Gen VI hybrid. It should accept Mark IV AND Gen VI heads. It has the later timing chain cover & oil pan and the one piece rear seal. It also has the bolt bosses for the lifter spider plate.

The aluminum heads should have Mark IV style locking rocker arm nuts. Do you have a head part number?

As lifters between small blocks and big blocks are interchangeable (not aftermarket which have tie-bars), you could lash them the same. I'd go 3/4 of a turn after the pushrod stops spinning in your fingers.
 

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Discussion Starter · #5 ·
The P/N for the heads is 12363392. Oddly, the documentation that came with the engine addresses the cylinder head installation but there is no mention about the lifter pre-load adjustment procedure.
 

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Discussion Starter · #7 ·
Took my right head off today. According to Summit I will get all my gaskets tomorrow so I should get it back together hopefully this weekend. The P/N on the head is actually a little different from the one in the engine paperwork.

The good thing is that everything looks real clean and the hone pattern is still visible. If anything, the engine runs rich, judging by the color of the combustion chamber. That should be cured when I switch to EFI.

The only spec I need is the lifter pre-load. I think I'll go with a 3/4 turn unless somebody knows for sure that it is something different.
 

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Discussion Starter · #8 ·
I owe an apology for asking the question and must have my head up my......when I was reading through my paperwork for the engine. A friend of mine was looking at the paperwork today trying to figure out the deck height. Anyway he instantly seen the valve lash specs:

"Valve Lash ................................................................. 1/8 turn down from 0"

I am glad because I was going to use a 3/4 turn. Thanks again to everybody who chimed in trying to help.
 
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