My used 2 hole head gasket measures 0.068" so I'm assuming that the head gasket thicknesses in the Bentley are "compressed".
If the pistons stick out 0.057" (max) and the head gasket is 0.0673" that gives ~0.010" piston to head clearance vs 0.020-0.023 called out in the Bentley.
Valve Reliefs in the ALH pistons are 0.038" and 0.041" in the PD150's so there is 0.003" there - plus I can sink the valves as deep as I want in the head very easily at this point. They're currently 0.030" out.
Rods are within 0.0005" of each other (ALH vs Rosten's) so that's good.
Wristpin to Top of Piston is within 0.0005" between the ALH and PD150 pistons so that's good.
The block was decked "less than 0.010" (pictures of that to come later, but it's interesting) so that's probably the main cause of the issue.
Thermal expansion of the rod and block should be similar, but the piston will grow disproportionately more being aluminum - will it grow 0.010" in length over the operating temp of the piston? I doubt it since it's only ~1.5" from the wristpin to the top of the piston.
I'm trying to talk myself into using a 3 hole head gasket and sinking the valves to 0.010-0.015" protrusion and not having to alter the rods like Matt suggested. Does anyone know the reason for having a 20-23 thousandths piston to head clearance? Is it for valve to piston clearance (which I can fix by adjusting valve protrusion) or is it for something I'm not accounting for above which would allow the piston and head to touch?
I've been trying to rationalize being able to make the reduced pistion to head clearance work without having to do creative machine work (see bold above). Running the pistons very close to the head does not bother me in concept, but discussing it with a friend of mine I decided to run a quick calculation on how much the pistion grows due to temperature.
There is ~1.5" of aluminum between the top of the pistion and the wristpin. Aluminum has a thermal expansion coefficient of ~0.000013 length/length/F so some quick bar napkin math gives us 0.0000195 in/F
I found this on passenger car diesel pistion temperatures and am currently in the 50kW/L area. Per the chart on page 4 (below), assuming that the average piston temp is 300C (572F), gives a ~500F change in pistion temp from room temperature where the piston protrusion measurements were taken.
0.0000195 in/F x 500F = 0.00975" taller piston at operating temps. Given the ~0.0100" piston to head clearance on the one piston mentioned above, that leaves veeerrrryyyy little clearance once things get hot.
This is just ballpark estimations here, but enough to convince me that I really can't put it together and have any expectation that the pistons won't hit the head eventually.
So - this weekend, I'll pull the bottom end apart again, measure everything up to see why there is a ~0.010" difference between pistions.
1) Take Piston & Rod 1 (that measured ~0.046" protrusion) and move it to cylinders 2, 3 & 4 and see what protrusions I get
2) Take Pistion & Rod 4 (that measured ~0.056" protrusion) and move it to cylinders 3, 2 & 1 and see what protrusions I get
3) Depending on what the above measurements come in at, it will hopefully show if there is variability in the piston/rod assembly or the crank throw/deck distance.
4) If it's in the piston/rod assembly, I'll mix/match rods and pistions to determine what parts are short/long
5) If it's in the crank/block then I'll probably turn the crank around and see if it's the crack or the block
Depending on what parts end up varying will determine what I do to attempt to correct it. I'll jump off that bridge when I get there