Leak Down Results on MHG before start up

[mic]

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.

[10sec.et]

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 .

[af2]

[Big Dave]

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

[Paul P]

Maybe there is shmeg in the gauge or air line causing fluctuation?

[SMOKEmUP]

[Paul P]

[Big Dave]

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

[squeeezer]

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

[mic]

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

[Paul P]

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.

[mic]

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.

[af2]

[10sec.et]

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.

[Paul P]