Piston ID for measuring deck height?

[Gaugster]

Can anyone identify a piston and/or provide a solid technique for measuring its compression height? I would like to document the deck height of a D3TE block by doing a partial reassembly of the old rotating assembly. Also has anyone figured out a good way to measure deck height of a bare block?

The markings on the 30 over piston are a "1139-89", "12-22" and either a "W" or and "M". I seem to be having trouble uploading pictures currently but will try again later.

[winr1]

On the piston, you can get close by using calipers from the top of the pin bore to the top of the piston

Measure on the other side of the direction notch

Add half of the pin diameter

Silvolite makes a 1139 piston with a comp height of 1.66



Ricky.

[frnkeore]

The way I do it, is to put it on a surface plate and measure to the top of the WP and subtract 1/2 of that. That will get you accuracy of .0005.

Calipers, will get about .002 accuracy.

You can get close, if you accurately measure the stroke, C/C length of the rod and piston compression height. Then install them (that one assembly), in each cylinder and measure the deck clearance. The clearance in each item, will make it impossible to get exact figures but, you should be able to come within .003/.004. You can't assume anything when measuring things. The temperature, will also effect your measurements. The standard is 20C or 68F. I always had to do my close tolerance measurements, in a temp controlled room.

For examples, 390 and up rod, is 6.488 +/- .002. My Speed Pro pistons are suppose to be 1.660 and they are 1.6575

[Gaugster]

Thanks for the information all. The pointer to Silvolite looks spot on as they look identical to what I pulled out. The 1.66" will be a good reference.

[My427stang]

If you expect great things or a good profit off the block, I'd likely just have it cleaned and measured on a fixture.

A 12 inch caliper on 4 corners subtracting half the main bore can give you a educated WAG, but hard to do both well and repeatable

Measuring the rotating assembly adds variables in stroke, bearing and pin clearance, rod length etc, plus takes a while

Not that it's quick for a machinist, but with a fixture you'll know the real number

[Gaugster]

If you expect great things or a good profit off the block, I'd likely just have it cleaned and measured on a fixture.

A 12 inch caliper on 4 corners subtracting half the main bore can give you a educated WAG, but hard to do both well and repeatable

Measuring the rotating assembly adds variables in stroke, bearing and pin clearance, rod length etc, plus takes a while

Not that it's quick for a machinist, but with a fixture you'll know the real number

I only have an 8 inch Mitutoyo caliper but you touched on my concern of finding a way to remove some of the stack ups associated with using the rotating parts. My goal is to understand if the decks have been cut previously so I can start the process of ordering custom pistons before the cost goes up.

I just measured from the top of the pin to the top of the piston. A total of eight measurements of four pistons. Also measured the diameter of the pins. Eight measurements also. Taking an average etc... I was able to calculate  1.6652" for compression height for the used parts. My garage is temperature control to some extent but nothing like a laboratory. So the 1.66" data seems legitimate.

[Gaugster]

Based on a bunch a measurements I have concluded that my 390 D4TE block has the factory deck height. My straight edge shows some variation but I plan to have it decked anyway.

As I am using old parts I moched up cylinders 1,5,4 & 8 with its own piston rod assembly.  With a deck bridge I measured an average piston depth of 0.1241". So 3.785/2 + 6.488 + 1.6652 + .1241" = 10.1698"

Dam close to the 10.17" OEM specification.