Deck Height help needed

[GMBulley]

Howdy all--

I have a semi-stock Type 4 hydraulic motor in my 1982 Vanagon for which I need a little guidance setting the deck height. Here is what I know.

The motor has a stock dimension counter-weighted crank, stock (balanced) rods, stock heads (very slightly flycut during rebuild), and set of slip-in, flat-top 96mm NPR piston/cylinders. I built it a few years ago and have a few thousand miles on the motor; today it has developed a head-to cylinder 'chirp' under full-throttle, low-speed acceleration that indicates a compression leak. I have re-torqued the head studs.

I did not use in-head seals (not called for in the 1982) or barrel shims, but the deck height (eyeballed) was within .5 mm of the top of the cylinder. Between the flycut on the heads, and the flat-top pistons, it would appear the compression ratio is too high.

The initial compression test (within 2k miles of building) indicated about 160 psi all around. However, the compression test now everything has settled in, (about 9k) indicates the compression is way high, at 185 on two cylinders, and 170 on the others. I'm going to pull the motor replace the rings, hone and shim the barrels.

My books give no help on setting deck height on a modified motor. How does one set the compression/deck height accurately, considering the modifications to this motor?
Also, any leads to decent 96mm rings (not Grant) appreciated.

[tuna]

Check out the Type 4rum here. You're bound to get a lot of helpful comments there.

As for the deck height, you will need to know the combustion chamber volume, the deck height (not eyeballed), bore, and stroke. We know the bore (96mm) and the stroke (71mm), but with the engine assembled, the other two pieces of the puzzle are unknown.

Get the engine apart, find this measurements and you'll be able to adjust your compression ratio to something you need.

Tom