Sounds like an air leak... how about sealant?

[ZombiePotatoSalad]

So I replaced the valves in my engine. Put the head back on with a new gasket. When I crank it, I hear a "pss-pss-pss" sound. A compression tester showed lower compression (around 70). I put one of these metal-looking gaskets on, but the original one was... fabric? Cloth? Whatever it's made of. Did I put the wrong gasket on?

And what about putting red gasket sealant around the perimeter of the mating surfaces of the cylinder head and block? Is that safe to do?

[Agemax]

Did you torque the head down properly, to the correct torque setting?

[ZombiePotatoSalad]

Did you torque the head down properly, to the correct torque setting?

Yes I did. I made sure of it.

[Agemax]

Are you 100% sure the camshaft timing is set correctly, and you have checked and adjusted the valve shims to the correct clearance spec.?

[1978GS750E]

And what about putting red gasket sealant around the perimeter of the mating surfaces of the cylinder head and block? Is that safe to do?[/QUOTE]

No sealant! Most of the newer head gaskets are a multi-layered metal type. Do you have the service manual? Have you followed the manuals' directions on installing the head? Where is the "air leak" coming from, carbs or exhaust?

Did you have the valves ground or lapped before installation? You can test the valve closure, by turning the head upside down with the spark plugs installed, and filling the combustion area with gas. If gas leaks out of the intake or exhaust port, your valve surfaces need work!

[ZombiePotatoSalad]

Yes, I checked the timing according to the manual. I counted the number of chain pins 3 times, just to make sure I got it right. When I did the valves, I both shone a light under them, and filled them with water. Nothing came through. I did lap them (that tool was annoying to use). It sounds like it's coming from the left side of the block.

[Burque73]

What a bummer. That's a lot of work, sorry to hear you'll have to tear into it again.

To isolate the leak, maybe spray some soapy water around the area and look for bubbles. Won't fix it obviously, but find the spot at least.

[1978GS750E]

Yank the valve cover off and make sure the #1 arrow is indeed in-line with the front gasket surface, (not above) and the ignition is lined up with the "T" when #1 piston is at top dead center. It's easy to have the timing off by 1 tooth if the exhaust cam is not positioned properly. (ask me how I know!) It's an easy check that doesn't take a lot of time.

[Agemax]

As you have replaced the valves, have you checked the valve clearances, and shimmed them to the correct service limit? If the clearances are too tight you will lose compression.

[ZombiePotatoSalad]

What a bummer. That's a lot of work, sorry to hear you'll have to tear into it again.

To isolate the leak, maybe spray some soapy water around the area and look for bubbles. Won't fix it obviously, but find the spot at least.

That's my next step. I tried cranking it earlier, but the battery didn't have much of a charge. I charged the battery and I'm going to try it again. I'm going to see if I can hear the air leak now when it's 20 degrees, and then in a couple days when it's 50. I think the cold might have caused the metal to contract enough to seal any leaks, but I'm not sure... SCIENCE!

[GS1150Pilot]

Uh, that sounds contrary to science, actually.

[ZombiePotatoSalad]

It's a joke. I'm doing what I can, with what limited resources I have. I don't even have a garage to work in, or money to go to a shop to get it properly fixed.
I had to sell my last vehicle, which had too many problems for me to fix. So now I have to get my bike running so I can sell or trade it for a vehicle, as I just started a job and we have a baby on the way.

[fastbysuzuki]

As been already said when you installed new valves (are they new or used) did you check the valve clearances? I would go back and check the valve timing.
did you check the condition of the head surface and for flatness as mls gaskets are not as forgiving as the old ones one other thing is have you used the cam tunnel oring as it should not be installed with the mls gasket.