Determining deck height questions

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Dave Whittick
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Determining deck height questions

#1 Post by Dave Whittick »

I've just got my heads back from Competition Engineering and I'm trying to figure out my deck height so that I can complete the assembly of my long block. I tried the method of using a piece of solder on the piston as per CE advice and I didn't get any crush even with no barrel shims. This suggests that the deck height is greater than the thickness of the solder or 1.6mm.

I checked the distance between the flycut surface of the head and the bottom of the chamber around the outside and it varies from 10.2mm down to 9.3mm which I thought was strange.

I checked the top of my AA 86mm barrels and the top flange is 11.2mm.

Does this mean that I should have the barrels turned down?

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Ron LaDow
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Re: Determining deck height questions

#2 Post by Ron LaDow »

Sounds that way to me, but try reading this:
https://precisionmatters.biz/pdf/compression-ratio.pdf
Ron LaDow
www.precisionmatters.biz

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Harlan Halsey
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Re: Determining deck height questions

#3 Post by Harlan Halsey »

Before cutting anything I would first determine what the situation is. If .060 solder tells you nothing why not try modeling clay?
My rule of thumb is that I want .050 minimum piston to head clearance, a compression ratio of 9.5 to one, and at least .020 clearance between the bottom of the head and the top fin.
How one achieves these depends on the condition of the parts you start with. I would be concerned if the depth of the cylinder seating surface was not the same around all cylinders and among all cylinders. The head volume can vary as the valves are ground and the seats resurfaced. Head volumes should be within 1cc.

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