Guys,
I’m finally getting around to final assembly and I was measuring deck heights today of my rebuilt short block. What I found is the passenger side is all about .016-.017 out of the hole (block was decked) but the driver side appears somewhat off. I’m measuring .018, .019, 020 and .022 from the front to the back with an average of .020 across that side. It just seems that this deck was cut at an angle .

Should I be a bit upset with my machinist or is this reasonable??

With the variance side to side (avg .004),, should I adjust gagket thickness?

Thanks!

 

Yeah I would wonder about that one. It's not to hard to get them within .001" on all 4 corners.

Bret

 

Decking a block is actually one of the easiest things to machine.
It should right on.

 

Do they not have a Block-tru fixture?

 

Im no machinist, but I would be showing the machine shop my pimp hand.

Either that or you are measuring it wrong, using a chickity china tool.

 

I use a Block Pro CNC vertical mill to deck my LS blocks. The reference is off the crankshaft centerline. I find that almost all of the blocks are ~.004" lower in the front vs. the rear.

 

That's damn interesting. Is that difference enough to cause a CR ratio difference that could account for the abundance of blown #7 pistons we always here about?

 

Howard is right about all used blocks being shorter at the front. The decks are always twisted as well. They will be about .005" lower on the exhaust side of cylinder 1 but less on the intake side. Also, most all blocks I have checked are higher for some reason on the right bank. Same front to rear deck height variance.

New blocks I check are pretty close front to rear but not left bank to right. It is not clear why the blocks tend to sag at the front. Motor mounts may have something to do with this.

In any event, if your block was decked off the mains, it should be a lot closer side to side and front to back than what you have. Use the same piston and rod to check all four corners of the block. Wrap masking tape evenly around the ring land area of the piston until it just fits in the bore. Measure at several points around the piston and average your readings.

Steve

 

From thermal loading?

 

Excellent points. You could be measuring a difference in the rod/pin/piston
assembly, and/or the piston has rocked in the bore.