MTFCA Forum

Brand-new first-time T owner, but long time Flathead ('53) truck owner. Compression check on my 1924 engine with a Z head shows only 25 PSI in the front two cylinders and 62 PSI in the rear. Engine was rebuilt recently by the previous owner so I assume my problem is a blown head gasket. The other problem is no one seems to have any copper head gaskets in stock. Will a steel gasket work OK with the aluminum head? Do you spray copper sealant on a steel gasket?

Before pulling the head I would check the valve gap. While it could be blown gasket, it could also be the gaps are not correct or miss adjusted and valves are not fully closing. How much has it been run and has the head been retorqued several times after running and cooling down? Do one step at a time, easy ones. First check head nut torque cold(45-50 FPs) then valves gaps before pulling the head. I would stick with the copper head gasket, they are out there and will take a little more searching. If you want to go with the composite type, stay away from the ones with the silicon beads, most folks have not had good luck with them.

All four cylinders should read about 100 psi with a Z head.

That engine must be too tired for the extra compression.

My rebuilt engine read 75 psi with just domed pistons.

I'm really wondering about the 100 psi expected with a Z head. I would expect more like 60-65 even on a fresh motor with the test being done at starter cranking speed on a warm motor with the throttle wide open and no extra oil added to the cylinder. Or.....(Maybe I need a new compression gauge).

Bruce Compton wrote: ↑

Sun Sep 13, 2020 10:30 pm

I'm really wondering about the 100 psi expected with a Z head. I would expect more like 60-65 even on a fresh motor with the test being done at starter cranking speed on a warm motor with the throttle wide open and no extra oil added to the cylinder. Or.....(Maybe I need a new compression gauge).

Agree Bruce. Atmospheric pressure at sea level is about 14.5. The Z head claims 6 to 1 compression so maximum would be 87 psi. On my engine with a Z head I get 75 psi on all 4. Also the gasket that Adam sells should work if yours has failed. https://mtfca.com/phpBB3/viewtopic.php?t=14933

Thanks for all the information. Well, finished the tear-down this morning and found the engine does have a blown (piece missing) copper head gasket between cylinders one and two and also looks like traces of a water jacket leak at the forward passage. Torque was low on several bolts. The pistons are .060 over, domed type. Engine was recently rebuilt by the previous owner as there was hardly had any carbon build up yet. The pistons in two cylinders that have been running cold even appear clean and shiny. Valves look great, very tight, clearances still at .015. Sent Adam an email hoping to find suitable gasket so I can see how it runs on all four cylinders!

I had a very similar problem with blowing head gaskets with a Z head. There is really not much material between the cylinders in a few places and even less material in the casting of the Z head in the same places ( less that 3/32"), and that's where the gasket lets go. After replacing three head gaskets, a race engine builder friend came up with a way to deal with the problem. He suggested I apply regular solder (using a soldering iron, not a torch) along the folded over edge of the fire ring on the copper head gasket, just enough to seal the gap (not a big lump) and explained that it would crush as the head was torqued down to provide a more secure seal between the cylinders. That was three years ago and I've had no problems since. Hope this helps.

Doug

Your engine should be just fine now with a new head gasket. My '27 is .060 and ran a Z head, no issues, but got a Prus head and put that on, with a new gasket and runs super.

Just a note on gasket install, all the other postings are correct on having the bolt holes clean, etc. Use Copper Coat or equiv. heavy metallic content Alum spray paint and coat the gasket. Fit the gasket with #4 and #1 @ TDC, to be sure the gasket is aligned.

Then run down the head bolts. Finally do the torque sequence shown, very important to torque first all the center bolts, as that is where the cylinder walls and the gasket is thinnest. Doing the squish there first is necessary, then go outboard and finish at the ends of the cylinder head.


Between the cylinders in the center is where most times the gasket goes.