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Leak Down Results on MHG before start up
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mic
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PostPosted: Sun Nov 11, 2012 1:15 pm    Post subject: Leak Down Results on MHG before start up Reply with quote

Still learning here. Should my leak down results be erratic before start up with new MHG? Are heat cycles necessary for proper gasket seal? I'm trying not to complete assembly before deciding whether to deck the block again or do composite gasket. Head was tested, machined .008, new stem seals. Compression was good before dis-assembly. Thanks for sharing your experience.
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10sec.et
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PostPosted: Sun Nov 11, 2012 6:51 pm    Post subject: Reply with quote

is this a completely new build or did you just change head gaskets ? are you doing leak-down or compression test ? you mention both. perhaps a bit more detailed info on exactly what you are doing would yield a better response Confused .
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af2
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PostPosted: Sun Nov 11, 2012 10:42 pm    Post subject: Reply with quote

10sec.et wrote:
is this a completely new build or did you just change head gaskets ? are you doing leak-down or compression test ? you mention both. perhaps a bit more detailed info on exactly what you are doing would yield a better response Confused .


Not only what was said but????? What is erratic and what is MHG??

See 10sec's sig first though. Laughing
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Big Dave
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PostPosted: Mon Nov 12, 2012 12:46 pm    Post subject: Reply with quote

The Composite Metal Head Gasket should seal completely once torqued . It doesn't require a heat cycle to seal.

If you are getting erratic readings (not sure what you are saying but I assume variation outside of 5% of the average pressure after throwing out the highest and the lowest reading) then your cylinders are not sealing. It could be a warped head or block out of square, or it could be the valves, or a cracked head (or block). If everything has been checked for cracks first you can eliminate that. If you have a new valve job that was done correctly then that can be eliminated leaving heat warped castings.

Big Dave
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Paul P
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PostPosted: Mon Nov 12, 2012 1:53 pm    Post subject: Reply with quote

Maybe there is shmeg in the gauge or air line causing fluctuation?
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PostPosted: Mon Nov 12, 2012 2:14 pm    Post subject: Reply with quote

Paul P wrote:
shmeg

New technical term?

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Paul P
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PostPosted: Mon Nov 12, 2012 3:20 pm    Post subject: Reply with quote

SMOKEmUP wrote:
Paul P wrote:
shmeg

New technical term?


I guess I should have said gurgling schmeg for technical clarity. Idea

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1971 - Chevelle 408 SBC N/A
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Big Dave
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PostPosted: Mon Nov 12, 2012 8:36 pm    Post subject: Reply with quote

I think his finger slipped off the "T" key and hit the "G" key just under it. My hands are old and arthritic and I use that excuse all the time when typing on my manual typewriter. May have to go back to smoke signals if I get any older.

Big Dave
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squeeezer
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PostPosted: Tue Nov 13, 2012 2:00 am    Post subject: Reply with quote

First q id have is why do you feel you need a leakdown or compression test???
What are you trying to diagnose???

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mic
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PostPosted: Tue Nov 13, 2012 10:02 am    Post subject: Reply with quote

Yes, I changed head gasket only and was wondering what other peoples leak down test results were before start up on their MLS or composite gaskets.

In my very limited experience it appears a system leak down test, before start up, with a new head gasket and less than perfect block deck may not be a good indicator of gasket seal. I assume that heat activates the cold sealers and some movement help the gasket to seal. Does anyone check a new gaskets seal before proceeding with assembly to avoid tearing it down again?

PS I try to ensure the rings have oil and rock cylinder away from and then back to TDC so compression ring will have some load when I LD test. Thanks
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Paul P
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PostPosted: Tue Nov 13, 2012 11:55 am    Post subject: Reply with quote

Leakdown tests should be done when the engine is hot. You should expect less than perfect results when cold but they should be consistent cylinder to cylinder. If the rings are gurgling oil because of the large end gap when cold that could also give you strange results.
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1971 - Chevelle 408 SBC N/A
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mic
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PostPosted: Tue Nov 13, 2012 2:53 pm    Post subject: Reply with quote

Thanks to everyone for the pointers.
I've now tried 3 different HG's (1 used, 2 new) and the pressure leakage as Dave described is well beyond the 5% on all of them. Maybe the deck is warped more than my carpenters square or piece of flat bar steel is showing me. (Anybody know of a cheap decent machinist level to buy or have a better method?) Yet each cylinder showed different results on each gasket. Anyway, I'm going with the composite gasket I'll let you know how it turns out. I'll be trying to stay out my own way so I don't shmeg things up!
I've seen people whose new weeping HG's made them wanna cry. Trying to avoid all that drama of having to dismantle everything again. Hopefully, more torque and less boost, for a while.
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af2
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PostPosted: Tue Nov 13, 2012 7:07 pm    Post subject: Reply with quote

mic wrote:
Thanks to everyone for the pointers.
I've now tried 3 different HG's (1 used, 2 new) and the pressure leakage as Dave described is well beyond the 5% on all of them. Maybe the deck is warped more than my carpenters square or piece of flat bar steel is showing me. (Anybody know of a cheap decent machinist level to buy or have a better method?) Yet each cylinder showed different results on each gasket. Anyway, I'm going with the composite gasket I'll let you know how it turns out. I'll be trying to stay out my own way so I don't shmeg things up!
I've seen people whose new weeping HG's made them wanna cry. Trying to avoid all that drama of having to dismantle everything again. Hopefully, more torque and less boost, for a while.


I have never leaked an engine cold.
I have never leaked an engine with new head gaskets cold.
I will never leaked an engine with 100,000 miles cold on it because the effort will always be the same.

So the question was weeeeping head gaskets? I don't think so.

I run MLS gaskets and have had them off 4 times to date to clearance the dome from hitting and closing the plug gap.. Same gaskets by the way.
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10sec.et
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PostPosted: Tue Nov 13, 2012 11:44 pm    Post subject: Reply with quote

what he said ^^^^^^

spray on a bit of copper coat and torque em down. if you have leak down/compression issues, it wont be the head gaskets.

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Paul P
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PostPosted: Wed Nov 14, 2012 10:30 am    Post subject: Reply with quote

Big Dave wrote:
I think his finger slipped off the "T" key and hit the "G" key just under it. My hands are old and arthritic and I use that excuse all the time when typing on my manual typewriter. May have to go back to smoke signals if I get any older.

Big Dave


Schmeg is short for Smegma. Spell check just would not get it right. Rolling Eyes

_________________
2001 Focus 2.0 Zetec
stock cams, bolt-ons and tune
15.63@87 MPH 1/4mi

1971 - Chevelle 408 SBC N/A
6.86@102.5 MPH 1/8mi
10.78@122 MPH 1/4mi
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