Ran a compression test today on the 77 302. They were all great between 120-95 all except cylinder 4 and 8. 4 had no compression and 8 seemed to only have 75. Is the poor reading on 8 due to 4? I pulled the valve cover off and everything is in place but I did notice that one valve was much cleaner then the rest...on 4! So what can I do to check? Also is it looking like I’m boned on this engine or should I continue?

 

A collapsed lifter or bent push rod. Pull the rocker arm assemblies. Remove the heads and have them gone through including magnafluxed for cracks. Inspect the push rods by rolling them on a flat surface.

 

Has this been setting for a length of time? May just be a valve stuck in guide from varnish in gas. As Red road says may not hurt to pull heads and have them re done. Looks like you could use a different manifold also.

 

it was sitting since 2010. It rolls over seemingly smooth and nice. Will I need any special tools diving into it that far?

 

is there any way to tell if the block is gonna be any good without having to take parts in and pay for something that may be a waste, ya know what I mean?

 

I wouldn't worry about the block at this point. Lay a straight edge over the rocker studs, it looks like number 4 has pulled up. Maybe just the photo angle. Also don't know if that would make different readings but looks odd. Only backyard mechanic here.

 

Not Really, no imho. Not if youre thinking for a proper rebuild. unless you have the tools for measuring and inspecting for cracks, then no.

This is what Ive done a few times in the past. If its a stuck vavle, and its stuck in the closed position the push rod is already bent. From the looks of the picture, it doesnt look like it to me, but impossible to tell from a pic.

Id remove the rocker, the push rod, and 'Stake' the valve. what that means is to use a rubber mallet, or carefully with a brass hammer tap on the vavle stem to see if moves. if it does, it should be pulled right back up by the springs. If it doesnt, even a little, means its sticking open. It may still be sticking open slightly, even if it isnt stuck, carbon on the seat etc which will affect your compressions. But be careful, if its stuck, dont hit too hard and bend the stem. Dont use a steel hammer directly on the stem. Normally you would presurize it too to blow the junk outward, but dont sweat it if you cant.

If it were stuck in the closed position I would have expected to see it partially open, bent rods and the rocker off to the side if it were running like that. And it will run, just will be missing on that cylinder, or more if more vavles are stuck. If I can find them, Ill post up a pic of what that looks like. In my expereince rods will look like Z's if the vavles are stuck in the closed position. If they stick once open, just the rocker will float all around and the rod will bounce around making a racket... youd shut it down pretty quick. Think rod bouncing off of lifters and vavle covers..

If youre on a tight budget, or really tight on time as I have been in the past, this is what I have done. (See pic below - 366 Chevy - Equipment truck that just had to get back into service asap - no time for machine shop work) Remove the head. You will neeed a valve depressor, try every vavle to see if they all move. If they do, remove the keepers (get a Chilton/Haynes manual), there are probaly youtube videos now on 'How To' now. Remove every valve, use some scotchbrith and lacquer thinnier to clean them up best possible, same with the guides If they are stuck, you will have to use a penetrating oil (I like AeroKroil) to get them moving. Again, use the mallet or brass hammer tapping on them. might take a few hours or days soaking them now and then. make sure the valve has somewhere to go, ie dont drive the valve it self into the work bench and bend the valve - youre sunk at that point. once you have them freed up, clean up the deck and head best you can by hand, no metal or high rpm tools, reassemble vavles, and re install heads with new gaskets. Its cheap, and gets you back in business.

If you have the budget and the time, and they are stuck, or needs a vavle job take them to a machine shop to get O/H'd. Quick test for vavles is to set the head on the bench upside down, and use gas in the chamber, see if the vavles will hold the gas. if not,the vavles and seats are probably needing attention. Again, if it just slowly weeps, and you just want to get back in serivice going down the road, re isntall and carry on.

these are the only pics i could find - these ones werre stuck in the open poistion.

366 Valves stuck in the open position on start up after sitting for long period and someone running ATF through the gas... Rods did not bend, just the vavles stuck in the open position.



If youre into removing heads, timing chain etc isnt that much more. Probably worth doing. This is similar to what itll look like when you tear it down. This one i decidede to do the cam and timing on it.


Cheers, Hope this helps you out.


Edit: the clean retainer makes me think it’s already been worked on.

Ive also had good luck running Marvel mystery oil in the crank case to free up sticky lifters.

 

The condition of the motor is an unknown. Do we know how many miles are on it? What are your long term plans for the truck? A reputable machine shop will build a set of heads for you from your magnafluxed heads or from a set of their known good cores and take your cores after they've been tested in exchange. They can use any of your parts that are reuseable. The main thing is if you're going to put the money into rebuilding you want to make sure you're starting with known good cores. This is not the place to cut corners. Same goes with the block if you get into it that far. You could also try and locate a running motor with good compression and run it while you work on your present motor.