So you run zero deck....

c.ruber · Posted: Thu Sep 11, 2014 4:15 pm Post subject: So you run zero deck....

So I'm having a bit of a dilemma. When I first built my engine I set the pistons and cylinders up for zero deck. I had to tear down the top end of my engine to correct a cylinder with low compression. I had all the cylinders honed for new rings and the pistons cleaned up. I'm mocking everything up and I have a problem with #3. I've swapped around pistons and cylinders and cylinders and pistons....still have the piston sticking out of the cylinder. Not much at all, but enough to feel when rolling the crank over to check the deck with a deck plate. Maybe at the most it's .002" I'm running a set of .045" copper head gaskets to get the compression ratio I want. I don't want to risk the piston smacking into anything...So what to do?? Should I take the piston to a known flat surface with some wet dry paper and gently remove enough of the face to make the clearance right (also considering the balance of the piston if it would be enough of a change to effect the balance)? Or should I find a machine shop to machine the face of the piston and rebalance the other pistons to match? Thanks for the input...
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[email protected] · Posted: Thu Sep 11, 2014 4:18 pm Post subject: Re: So you run zero deck....

List the #s of all 4 cylinders; the deviation is what you are looking for.
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modok · Posted: Thu Sep 11, 2014 4:24 pm Post subject:

Could also swap to .050 gaskets on that side, or replace rod bushing to have the rod shortened a few thou.

Or just run it. .040 won't hit if it's really .040

c.ruber · Posted: Thu Sep 11, 2014 4:33 pm Post subject:

I'm a little concerned about expansion at running temp with the piston sticking out of the cylinder even that small amount... Am I crazy?
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[email protected] · Posted: Thu Sep 11, 2014 4:36 pm Post subject:

It doesn't matter if the head gasket is bigger than the piston on the ID. I have run .028" clearance to 8k RPM.

Alternatively you can run a .060" gasket and move forward.
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c.ruber · Posted: Thu Sep 11, 2014 4:36 pm Post subject:

I'm not sure I'm following what you are trying to tell me John... I've swapped the pistons and cylinders all around and am still having the same issue on that particular cylinder spigot on the case. I'm thinking the case has given way a little since I first assembled the engine some time ago due to wear.
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[email protected] · Posted: Thu Sep 11, 2014 4:37 pm Post subject:

Did you check the case spigot deck prior to assy?
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mcmscott · Posted: Thu Sep 11, 2014 4:38 pm Post subject:

Image may have been reduced in size. Click image to view fullscreen.

On my performance engines I get the deck within .001" of each other, then rebalance. Sometimes you have to get creative
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c.ruber · Posted: Thu Sep 11, 2014 4:41 pm Post subject:

John, I had the case decked when I had all the machine work done prior to initial assembly. The case has a few years of weekend beating on it. I'm not sure how to check the cylinder spigot at this time...
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modok · Posted: Thu Sep 11, 2014 4:44 pm Post subject:

[email protected] · Posted: Thu Sep 11, 2014 5:02 pm Post subject:

re-check the case deck NOW. Sure it was close a few years ago, but that's not doing you much good now. Check it!

Once you know, these guys here will give you several solutions to fix it right, quickly. Samba guys are sharp!
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c.ruber · Posted: Thu Sep 11, 2014 5:18 pm Post subject:

OK John... How do I check the case?
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mcmscott · Posted: Thu Sep 11, 2014 5:35 pm Post subject:

c.ruber · Posted: Fri Sep 12, 2014 8:51 am Post subject:

If I opt to remove some material from the face of the piston, how much of a difference in weight would require me to rebalance the pistons?
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mark tucker · Posted: Fri Sep 12, 2014 9:10 am Post subject:

what john is saying he has run .028 with no issues. I run .033 with no issues. some people run .08o" with issues...... you may try another set of shims as there may be a varriance of .002 or more between brands/batches.

Max Welton · Posted: Fri Sep 12, 2014 9:59 am Post subject:

Bashr52 · Posted: Fri Sep 12, 2014 10:12 am Post subject:

c.ruber · Posted: Fri Sep 12, 2014 11:26 am Post subject:

That works for me.... I'll recheck that. Thanks.
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Max Welton · Posted: Fri Sep 12, 2014 12:51 pm Post subject:

mark tucker · Posted: Sat Sep 13, 2014 9:27 am Post subject:

be sure the cylinders are down good and not on bent shim,stud thread,casesavor etc. you should still have some way to hold them down to check this.also be sure there isant any burr or interfearance in any way that might hold one up.


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