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> Deck Height Question
clarkcou
post Nov 28 2020, 09:16 PM
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Building a 1.7, 90 mm piston/cylinder. With no base gasket, deck height is .013in. Shouldn’t the head gasket/ shim be included in the deck height.

Barrel shim, not yet installed, is .21mm. Head gasket is .068.

Seems to me that deck height would be.082 without barrel shim. I.e. .013 plus .068.

Thoughts on this please?

Randy
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Montreal914
post Nov 28 2020, 09:48 PM
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I am sure others will chime in but per Porsche bulletin many years ago, head gasket are not recommended. 0.040" is the "standard" deck height you are looking for. Shims should go under the barrels. I had a custom thickness one machined for me on my rebuild. Not sure multiple stacked ones are recommended, I doubt it.

That being said, head chamber volume, and deck height should all be considered to calculate your compression ratio, assuming you have flat pistons.

Good luck with the rebuild.

Edit: Sorry, to answer your question, yes under barrel shims should be considered in the deck height measurement and cylinders should be held down on the block with head torque value simulating assembly.
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Robarabian
post Nov 28 2020, 10:10 PM
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They sell a kit to help with it... a deck height measurement kit. No head gaskets / shims. Put the base shim and assemble the cylinder. Using the kit, it will bolt down under pressure (torque spec not necessary but likely used) and measure the deck height. You want .040 to .060.. somewhere in that range. Do the math and calculate the base shim you will need to meet the deck height. Make sure you take the CC of the heads into consideration for compression ratio calculations...

Have fun!


QUOTE(clarkcou @ Nov 28 2020, 07:16 PM) *

Building a 1.7, 90 mm piston/cylinder. With no base gasket, deck height is .013in. Shouldn’t the head gasket/ shim be included in the deck height.

Barrel shim, not yet installed, is .21mm. Head gasket is .068.

Seems to me that deck height would be.082 without barrel shim. I.e. .013 plus .068.

Thoughts on this please?

Randy

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VaccaRabite
post Dec 1 2020, 11:59 AM
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QUOTE(Robarabian @ Nov 28 2020, 11:10 PM) *

They sell a kit to help with it... a deck height measurement kit. No head gaskets / shims. Put the base shim and assemble the cylinder. Using the kit, it will bolt down under pressure (torque spec not necessary but likely used) and measure the deck height. You want .040 to .060.. somewhere in that range. Do the math and calculate the base shim you will need to meet the deck height. Make sure you take the CC of the heads into consideration for compression ratio calculations...

Have fun!

The old school way to do this is not to use a kit, but to use 2 sockets that fit over the stud and use them to bolt down the cylinder to measure deck height.

Also DON"T JUST PICK A DECK HEIGHT!

Deck height is only a part of your Compression Ratio calculation. You want to pick a CR, and then use Deck Height to get to it. Don't just build to the smallest deck height and hope for the best. I've done it. And I've torn the engine down a few months later too.

.040 is the minimum safe deck height in terms of valves not hitting pistons. You can build an engine with too little deck, which equals too much CR, and be constantly battling overheating heads. Being forced to drive around in 4th all the time or watch head temps hop over 400 degrees SUCKS.

Zach
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