New Head Gasket - now no compression..

Chuck Dempsey

Chuck Dempsey

Well-known member
I put a new head gasket on my 1930 engine, using Snyder's 'Premium Head Gasket'. I gradually tightened all of the head nuts to 55 f/p. When I turn the engine over 'by hand', it seems there is very little compression. I can hear air being pulled through the carb. I haven't tried to start the engine yet. Is this normal, or have I really hosed something up? Thanks
 
Did you check the head and block for flatness while the head was off?

This gasket style will not squish as much as a thicker multiple layer head gasket, to make up for the head or block not being perfectly flat.

I'd suggest you start and run it, per Snyder's instructions. Nothing to lose at this point.
 
To what John said - one time when I was reinstalling a head after gasket replacement I must have let the head down a bit too vigorously, bent a valve. It ran, but only on three cylinders. Obvious on compression test.
 
Did you clean the head and block with an acetone wipe as a final step? As Jim said in post #2, were the head and block flat? There should be less than 0.002 gap anywhere.

I have had very bad luck with the premium head gasket. The head gasket on my car now, and the one that works best for me, is the Best brand graphite gasket with a coating of the spray copper gasket sealer on both sides of the gasket.
 
nkaminar said:
Did you clean the head and block with an acetone wipe as a final step? As Jim said in post #2, were the head and block flat? There should be less than 0.002 gap anywhere.

I have had very bad luck with the premium head gasket. The head gasket on my car now, and the one that works best for me, is the Best brand graphite gasket with a coating of the spray copper gasket sealer on both sides of the gasket.
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My experience also, leaked even with a freshly decked head. Best 509G with copper spray is my go-to head gasket now.
 
I have the Burtz 6 + head and, yes, the 509G. By the way, after the wipe with the acetone, you can fill any divots with JB Weld, 24 hour cure. After it is cured you can sand it flat to the surface with some wet and dry sand paper wrapped around a flat file. 220 grit is OK.
 
It’s quite possible that some debris (carbon,gasket scrapings etc) got between the valve and the seat and that it will clear after running or cranking a lot.
Another method I have used to clear debris from valve seats is introducing air under pressure and cranking the engine over .
 
All, thanks for the replies and suggestions. I did have the head evened, but the block is still installed. The head seemed to go down the studs evenly, and slowly. I had to pound it a tad at the bottom to get it all the way down. A friend wondered if air might be escaping around the piston rings, since I had the head off for around three weeks. He suggested I pour a bit of oil into each cylinder and 'hand crank' it to see it that helps...
 
A person can tweek the studs a bit in order to allow the gasket to easily drop down on the deck prior to using the copper coat or aluminum pigment silver rattle can paint. I've had more success getting the head to also drop down easily that way.

I also turn the engine through to insure all eight valves open and close normally prior to head installation. Valves can get bent if it was necessarily to unstick some after the head was removed.

If the cylinders have been bored a good bit oversize then the distance between cylinders decreases as well. I believe it's the #8 stud where the electro lock clamp installs that can be hard to seal in that location with large bore sizes. Taking the nut loose there to install the ignition cable clamp can be problematic on some engines. It's best to put all the nuts on for keeps when installing and torquing the head.
 
Chuck Dempsey said:
A friend wondered if air might be escaping around the piston rings, since I had the head off for around three weeks. He suggested I pour a bit of oil into each cylinder and 'hand crank' it to see it that helps...
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I think that is an excellent suggestion. Not too much oil, and start the engine outside, because it will smoke like crazy at first.

Honestly, I would just start it and run it for a few minutes. It will seat itself. Re-torque when cold again.
 
Jim/GA said:
I think that is an excellent suggestion. Not too much oil, and start the engine outside, because it will smoke like crazy at first.

Honestly, I would just start it and run it for a few minutes. It will seat itself. Re-torque when cold again.
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Expanding on what Jim wrote, I would heat cycle and re-torque a few times before calling it a failure.
 
Crud can get down around the piston gaps during cleaning so that can fowl the top ring. If it's old carbon sticking the rings, I use Marvel Mystery Oil or even Hoppes #9 to soften the carbon. That and turning the engine may help enough to get compression for it to run. If it starts and runs then use the MMO in the fuel to free everything up. The heat will get things moving if it runs as has already been mentioned.

If the compression is still low then it could have a broken ring. Crud on the valve seats should blow off if it will start.
 
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