Tips and advice appreciated...

[briarpatch]

I recently replaced the in/ex manifolds on the '70 C10 w/ 250 L6. It runs better and I have eliminated the pesky exhaust leaks that it previously had.

An ace mechanic friend of mine ran a compression test on the cylinders and found two adjacent ones running at low compression (25 and 40 psi, other 4 were right on at 130psi). He recommended replacing the head gasket as it is likely to be blown between the two low compression cylinders.

I would appreciate any tips and advice in replacing the head gasket. I have never replaced one and others have told me it will be "easy" to do. I'd just be more comfortable hearing from some of you experts before I dive in!

I have the gasket and am ready to go...Thanks.

[64fleetside]

Easy job on the six, just remove headbolts, head, clean surface, re-install. Be careful with the front two head bolts they are thru to water jacket in a thin area, most recommend going easier on the torque there. Use a shop crane or hoist as head will be heavy, you can leave the manifolds attached. You will have to remove pushrods & adjust the rockers when finished. Brian

[Fred T]

Cleanliness is next to Godliness, and you want to be as clean as possible. Since you had the manifolds off, the job will be easier. I don't remove the manifolds from the exhaust unless I need to for cleaning. A piece of lumber and some tie wire to hold the manifolds up after they are unbolted from the head.

After the head is off, I fill the cylinders with rags and start cleaning the block deck. I usually scrape off all the gunk and as much gasket as I can, then I use a wire cup brush in my angle grinder or drill motor to finish cleaning. Use the same method on the head. Carefully remove the rags and vacuum all the crud I can out of the cylinders, followed by wiping down the walls. If there is much carbon build-up on the pistons, this is a good time for scraping the piston tops. Take a tap and clean out all bolt holes. I then take my air gun and blow out the cylinders. More wiping down, followed by a final wipe on the cylinder walls with an oil rage. Clean all surfaces that mate to gaskets with lacquer thinner. I also use only Fel-Pro gaskets, no Asian imports. New head bolts, while not a requirement, are a good idea. 35 years of abuse takes it's toll.

When assembling I use Permatex teflon thread paste on the head bolts. It will stay soft and pliable for retorquing later. Follow the torque pattern (in the shop manual) and torque in 3 steps. Don't forget the right front bolt has a lesser torque value, to keep from cracking the head.

On the manifolds, I usually use a thin layer of ultra-copper RTV on the gaskets, it helps a lot if there are any exhaust leaks. Be sure it cures for 12 hours before starting the engine.

Valve cover gaskets are another leak problem. I use a cork gsket with 3M weatherstrip adhesive. Be sure to straighten the valve cover first.

[pjmoreland]

I had two adjacent cylinders with low compression on a V8. When I took the head off, I discovered that the two exhaust valves were cracked, and that the cam shaft was so worn out that it wasn't lifting these two valves at all. The head gasket looked fine. I would recommend removing the valve rocker cover and crank the engine over by hand a few times to make sure you can see all of the valve rockers moving up and down as they should. Make sure to inspect your valves once you get the head off.

[chevydog66]

Did you mean header gasket or head gasket?

[68C15]

pjmoreland is on to something IMO. I suspect you have either bad valves or flat cam lobes/mushroomed lifters. this is why I ended up swapping to a V8. follow his advice

[briarpatch]

Originally Posted by chevydog66

Did you mean header gasket or head gasket?

chevydog66 -- It's the cylinder head gasget.