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Old 03-18-2013, 06:24 PM   #1
shjeeper
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Head Bolts - Tighten a bit more?

I recently replace the head on my SPI motor.. New gasket, bolts and all that good stuff. I ran it for 1k miles and tested the compression..

Cyl 1: 175
Cyl 2: 180
Cyl 3: 182
Cyl 4: 180

Should/Can I attempt to tighten those first two bolts by the 1st cylinder just a tad bit? Or should I just be happy it's within 3% of the others?

Or.. should I first throw a tad bit of oil into that cylinder to make sure the rings are just wearing out?


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Old 03-18-2013, 07:33 PM   #2
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Please tell me this is a joke.
You are not serious are you?
If you are serious, you need to put any tools you have down immediately and step back from the car. Please call a professional.
The head bolts have nothing to do with your compression. Compression is a function of valve timing, ring wear and swept to clearance volume.
Your compression is fine.
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Old 03-18-2013, 08:11 PM   #3
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Quote:
Originally Posted by paulg127 View Post
Please tell me this is a joke.
You are not serious are you?
If you are serious, you need to put any tools you have down immediately and step back from the car. Please call a professional.
The head bolts have nothing to do with your compression. Compression is a function of valve timing, ring wear and swept to clearance volume.
Your compression is fine.
#1) This forum isn't just for professionals right? We both know the answer to that - which means that DIY people may discuss options here. So instead of implying that I have no idea what I'm talking about (and/or stupid), correct me where I'm wrong and keep your childish comments to yourself. We all begin with little/no knowledge on turning a wrench, and we learn by asking questions.

#2) Low compression can be caused via a blown head gasket.

So now lets step back and think about this, if the head bolts aren't tightened correct you could end up with a warped head.. or just a head that isn't tightened completely, resulting in the head gasket not sealing completely. So while the compression is within specs, I'm wondering about the possibility of tightening the two head bolts to the left of the 1st cylinder. Doing so would further compress the head gasket a bit more. I'm thinking only 1/10th of a turn, but I'd like some input on it.
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Old 03-18-2013, 08:19 PM   #4
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That is not low compression. 80 is low compression. 3% difference between cylinders is very good.
A blown head gasked also dumps coolant to oil, causes bubbling in the coolant, along with very low compression.
If you torqued the bolts to spec, with oil or whatever lubricant the hardware called for, then it you start to overtighten them the material will start to yeild, resulting in a loss of clamp load.

Sorry to give you the business, it's just that I have NEVER heard anyone ask that question before. I figured anyone that could change their own head gasket would know the answer to this question. Sorry about that.
Go and enjoy your successful gasket change!!
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Old 03-18-2013, 08:41 PM   #5
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Ford actually doesn't state a value or minimum for compression readings. Instead they only state that compression measured between cylinders should be within 25%. Unless that's been changed and published somewhere.
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Old 03-18-2013, 08:45 PM   #6
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Quote:
Originally Posted by paulg127 View Post
That is not low compression. 80 is low compression. 3% difference between cylinders is very good.
A blown head gasked also dumps coolant to oil, causes bubbling in the coolant, along with very low compression.
If you torqued the bolts to spec, with oil or whatever lubricant the hardware called for, then it you start to overtighten them the material will start to yeild, resulting in a loss of clamp load.

Sorry to give you the business, it's just that I have NEVER heard anyone ask that question before. I figured anyone that could change their own head gasket would know the answer to this question. Sorry about that.
Go and enjoy your successful gasket change!!
While I understand the idea/purpose of torque-to-yield, I wasn't sure if attempting to tighten a bit more would change anything. Thanks for explaining it though, I appreciate it!

And.. no hard feelings. :D
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Old 03-18-2013, 09:22 PM   #7
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My Cyl. 1 compression, before the timing belt blew up, were exactly the same as yours. Cyl 1 was in the 175ish mark and the rest were in the 180ish mark. A delta of 15 psi is acceptable.

...the timing belt had nothing to do with my compression. Well it does now while it's at 0 PSI.
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Old 03-18-2013, 10:05 PM   #8
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Quote:
Originally Posted by a_2000_se View Post
Ford actually doesn't state a value or minimum for compression readings. Instead they only state that compression measured between cylinders should be within 25%. Unless that's been changed and published somewhere.
I just purchased a couple days of the workshop manual - I didn't see anything different from the 25% you mentioned. Thanks everyone!
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Old 03-19-2013, 01:00 AM   #9
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For torque to yield bolts do not retighten them.
If you tightened them according to the bolt pattern and the series of steps required when initially tightening them, leave them be unless you want to remove them and replace them.
Do not 'fix' what is not broken.
Over doing things creates super messed up stuff.
So with your current readings all is fine.
Leave the bolts alone.
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Old 03-19-2013, 01:39 AM   #10
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negative comments aside, as others have said, don't touch them.

I know there's all kinds of numbers but if a cylinder is more than 20% off from any others, there's a problem. that looks pretty good.
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