Deck height measurements driving me crazy, Need advice Options

[stugray]

Ok, so I bought the deck height measurement tools from the group buy.
But I cannot figure out exactly how the OP intended to use the middle plate.

I have been trying to measure my deck height accurately for weeks now and I either am not doing it right, or I have a problem.

I have the EMW AA cylinders & KB Hypereutectic pistons - brand new.
I am measuring with no shims under the cyls.
I bolt the holddown tool on two cyls with pistons installed and torque to spec (24 ft-lbs)

I set TDC on the cyl I am about to measure with a mag base & dial indicator using the middle of the piston as reference.

I then set a VERY straight edge across both cylinders and clamp it down.
I then measure the top of the cylinder mating surface down to the very edge of the piston using a dial indicator/depth gauge.
I repeat the measurement at least 5 times and average the results.

I am getting measurements that vary from .022 to .032 and they can vary by up to .0067 across a single piston (front to rear). (IMG:style_emoticons/default/WTF.gif)
(measurements at the same spot are repeateable within less than .001)

When we are trying to get these deck heights to match to within a few thousandths, I cannot see how that can be done when the piston can be off by more than 5 thousandths front to rear.

Does this mean I have bent rods or misaligned wrist pin bushings?

I had the entire rotating assembly balanced, so I would hope they would have caught something bent.


I guess my next steps will be to shuffle the pistons around and see if the measurements follow the pistons.
If they dont, I might need to move rods.
Can all 4 rods be removed & replaced without splitting the case again?

Stu

[VaccaRabite]

When I did mine I measured from the exact center of the piston to minimize the rocking, and did it w/o any rings on the pistons.

What is your target compression ratio?

Deck height is important because that is one of the variables in your compression ratio. Shims make a difference because that is how you get your deck height the same between all the cylinders. Measuring w/o shims is kind of pointless.

You start with the target deck height to need to get to the ideal compression ratio. Add shims to get that deck height on all 4 corners.

If the .022 to .032 delta is between cylinder of opposite banks, you are probably fine. Once you shim the bases of the cylinders they will be the same. If the .022 to .032 delta is on the same bank (IE - the 1,2 bank or the 3,4 bank) you may have head sealing issues on that side. The cause will be the case registers, which should have been checked while the case was at your machinist. Its one of those things that many machinists don't know to do unless we ask them. The registers on my case had to come down quite a bit to get them even, and were the cause of a head leak which made me tear down the engine for rebuilding in the first place.

Zach