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Head Milling / Timing

 
Old 02-03-2019, 06:39 AM
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Default Head Milling / Timing

I have read through many threads on this topic but can't seem to find a definitive answer, so starting a new one here.
My MY04 was down on power and idling rough, so I did a leak down test and discovered the head gasket was leaking between cylinders 1&2, and 2&3.
Pulled the head and put a straight edge on it. There's definitely some warpage, but less than .008"
If I have the head machined flat and they take off less than the .008" max (per the Honda service manual), do I have to worry about making any timing adjustments?
The Honda manual doesn't address this.
I plan to use the OEM head gasket.
For reference, the car is bone stock with the exception of a Billman GenX TCT.

Appreciate any feedback I can get, thanks
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Old 02-03-2019, 07:05 AM
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You can actually mill the head a lot more than .008" and not have valve clearance issues. The timing will be thrown off a little bit milling the head, but not really enough for you to notice a power difference. If you are concerned you can get adjustable cam gears.
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Old 02-04-2019, 04:18 AM
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Thanks for the reply Charper732. By my measurements, the head warpage is only about .003"-.004", so I don't think the shop will need to mill more than that hopefully.
I'll update once I have everything back together.
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Old 02-04-2019, 04:44 AM
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Any head mill more than .004 will skew the chain geometry, and accelerate wear of the chain and sprockets. A head gasket with comparable thickness added will put it back in range.

The limit it the manual does not account for the ongoing timing chain issue, where the current chain geo is near the limit.

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Old 02-04-2019, 06:48 AM
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Originally Posted by Billman250 View Post
Any head mill more than .004 will skew the chain geometry, and accelerate wear of the chain and sprockets. A head gasket with comparable thickness added will put it back in range.

The limit it the manual does not account for the ongoing timing chain issue, where the current chain geo is near the limit.

Thanks, again for injecting your experience in these matters. So for any head or block, measuring warped; needing 0.004" milling or greater --- prolly best to look for another undamaged head or block?
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Old 02-04-2019, 08:00 AM
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A used part has its own risks. It maybe flat, but have other damage that is not immediately obvious.

Billman just said its ok to mill so long as you add back what was milled with that much thicker head gasket. If your only.issue is warped head, and you know the history of the motor otherwise (or at least have enough history to know there are no other significant issues with it), I would think it wiser to fimd out how much needs to be milled, then find what head gaskets are available, then mill motor to the gasket you'll use (mill it so with that gasket, its back to stock geometry).
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Old 02-06-2019, 07:57 AM
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Thanks everyone for the great input. I received the head back and the shop milled .012".
The OEM head gasket is .030".
So, following Billman's advice, I should run a slightly thicker head gasket in the .040" range?

Does .012" (12 thousandths) make that much of a difference? I'm not questioning the experts here, just want to make sure that I have my decimals right.

thanks again

Last edited by DhaughnS2K; 02-06-2019 at 02:07 PM. Reason: correction to measurement
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Old 02-07-2019, 05:34 PM
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Any thoughts on my last post? I’m ready to order the Cometic 87.5mm 0.04” gasket but want to make sure I’m doing the right thing here. Thanks again everyone who contributed information to this thread
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Old 02-07-2019, 05:43 PM
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.012 is a lot to remove as far as the chain is concerned.

If they took off .012, and you are adding .010 with the new gasket, that is the right move.
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Old 02-08-2019, 07:24 AM
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Increasing the thickness of the HG increases the squish area in the combustion chamber, so I wouldn't go too thick. Increasing the squish area too much leads to combustion instability.

http://www.nrhsperformance.com/tech_squish.shtml

Therefore one must consider both chain geometry, and effects on combustion from a thicker head gasket and arrive at a compromise.
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