350 Zero Compression #3 and #5

[pilotXC]

My truck all of a sudden starting pining really bad under load or acceleration about 3-4 weeks ago and I thought it was bad gas, so drained the tanks and started with new gas, didn't help. Checked the timing, it was fine. Checked plugs, looked good. Checked the cap and rotor, all contact points were terrible, so I replaced and no change. Finally thought it was a carb problem, so rebuild the carb and found the primary side very dirty so thought for sure it was leaning out under load and it would be fixed, no change. Did a compression test at a local shop, #3 and #5 have zero compression. Temp is normal on the gauge and seems normal under the hood, oil pressure is good on the gauge (same as it's always been). The shop said it's not a head gasket and that there is a crack in the block between the cylinders, but that would show in water in the exhaust or in the crank case, or something somewhere? Haven't done a leak down test, but just curious if anyone has had any similar issues. Would zero compression create a knocking noise?

[mongocanfly]

zero compression will cause all kinds of issues....you sure wont be able to do a leakdown test on 3&5...
if it has no compression sounds like the heads will be coming off at the least....could be bent valves or blown head gasket

[PGSigns]

Well if it were a crack I would expect it to be a big one to kill the 2 cylinders and you would have water. I could easily be a head gasket between the two cylinders. If it has been a while it could have scorched the deck and the head surface. Heads need to come off to see what has gone south and make a plan on what to do from there.
Jimmy

[Dead Parrot]

Possible the thermostat stuck shut or nearly so long enough to cause an overheat, the pinging and resulting loss of compression. Happened to my father many years ago on his way to work. Result was a cracked/blown head gasket between two cylinders. Didn't otherwise do much harm. Pulled the heads, had a valve job done since the heads were off anyway, replaced the gaskets and thermostat. Engine was good for many more years. It was long enough ago I don't remember what noises the motor was making before the repair.

If it did do a one time overheat, could have blown one of the exhaust gaskets in the process.

[sweetk30]

make sure both have closed valves . push air in 1 and see if it comes out the other plug hole . if so popped head gasket or cracked head .

[pilotXC]

Thanks everyone... At the very least, looks like I'm pulling the head, but will try to do a leak down to see if I can find where the compression is going first.

[PGSigns]

If you have zero on the two cylinders a leak down is not going to tell you much more than the compression gauge. Just pull the head.
Jimmy

[mattfranklin]

Sounds way more like a failed head gasket than a cracked block. Especially with the zero compression on adjacent cylinders.

Not sure how a shop could be so confident it was not a gasket issue given these obvious symptoms. Unless you have the lightweighted scalloped '624 heads and they are assuming the worst.

[pilotXC]

When I picked it up they said, maybe it's a head gasket that's causing the compression problem, but that wouldn't fix the pinging/knocking sound. Haven't had time to dig into it more yet and not looking forward to finding a broken piston skirt or something, so have been kind of delaying the inevitable...

[mattfranklin]

Originally Posted by pilotXC

When I picked it up they said, maybe it's a head gasket that's causing the compression problem, but that wouldn't fix the pinging/knocking sound. Haven't had time to dig into it more yet and not looking forward to finding a broken piston skirt or something, so have been kind of delaying the inevitable...

Good luck with it and let us know what you guy find.

[pilotXC]

Thanks... I confirmed air between the 3 and 5 cylinders this afternoon. Just a matter of if it's a gasket issue, head issue, or block issue. Going to start by pulling the head and seeing what I can figure out from the top of the engine and go from there...

[geezer#99]

When you pull the head off could you take a pic of it. Just the valve side will do.

[sweetk30]

seen a few with popped gaskets between the cylinders . cleaned up surfaces and made sure all was good and smacked on new gasket SET since your all the way in there do both and they were good after the new gasket .

[HO455]

Originally Posted by pilotXC

Thanks... I confirmed air between the 3 and 5 cylinders this afternoon. Just a matter of if it's a gasket issue, head issue, or block issue. Going to start by pulling the head and seeing what I can figure out from the top of the engine and go from there...

Good luck! Hoping for a bad gasket.

[pilotXC]

Finally pulled the head today and sure enough, the gasket was gone between 3 and 5. Anyone have any thoughts on if this would cause a ping/knock under load?

[mongocanfly]

Wow...you found it...I'd get the head checked for warpage while you got it off....

[pilotXC]

Originally Posted by mongocanfly

Wow...you found it...I'd get the head checked for warpage while you got it off....

Suffice to say, I'm happy that's what it was... I haven't pulled the other head yet. Need to do some calling around for machine work/valve job and see if anyone will tell me if the head is indeed not warped, just to be sure as you said. I put a square up to it, and from what I can see with that, looks pretty straight, but I'm sure a machine shop can say for certain.

Also, from the top side, no sign of scoring or anything on the cylinder walls. Been told the noise was likely a broken piston skirt, cracked piston skirt, or wrist pin. Not sure if that would show from the top, I turned the engine over 2 rotations after taking the head off to check the walls. I know I'm trying to make this easier than it might be, but it seems like fuel being pushed back and forth from cylinders would create some havoc and noise of pre-detonation, exhaust pushed back and forth, compression being pushed into the intake? I'm just not sure what part of the stroke 5 is in when 3 is on compression and vice versa and what results that would have on the other cylinder?

[mongocanfly]

Only way to know for sure about pistons is pull the oil pan...

[cadillac_al]

The stock steel shim gasket wouldn't do that. I don't know why people buy those thick gaskets unless they know the heads are warped.

[vince1]

After getting the head checked for straightness I'd just put a gasket in and carry on. Probably the noise you heard was from air across the cylinders.

It looks like you have some ridge on the cylinder walls so a rebuild could be in its not too distant future.

[truck-kid]

Hard to tell from pictures for sure but appears that gasket bore is to small for your bore size .Looks like it was hanging into the bore when compressed.

[Dead Parrot]

#3 is two before #5 in the firing order. Possible the fire from #3 was lighting #5 near enough to the start of the compression stroke on #5 that it was trying to compress a burning charge. If so, that would probably make interesting noises even with the lack of compression seal.

You are going to be doing an oil change anyway. Screen the oil for metal debris. Cut apart the filter and do the same. If that looks good, verify the heads are in good shape, install new gaskets and fire it up.

[pilotXC]

Thanks for everyone's comments and help...

I was overly optimistic when I pulled the head and saw the gasket popped between the cylinders. I sent a picture to a friend and saw him the next day, he said, "did you look at these pictures?" Yes, of course. "Did you see this crack?" F$%&!!!!!

If you look closely behind the water mark on the picture of the block, there is a hairline crack between the 3 and 5 cylinder. Block is fubarred. Most likely that's why the head gasket went. I have not over-heated the engine, but I did have to get the radiator rebuilt about a year ago so it could have ran super hot from the previous owner at some point, or the low fluid for who knows how long before I had it could have over time just caused the crack? No idea. Needless to say, I'm very discouraged and disappointed and not sure what I'm going to do at this point.

Considering just throwing a head gasket on and put it back together and drive it until I can find the funds for something else. The block is screwed anyway, unless someone would be willing to sleeve it I suppose? But maybe the gasket will go immediately again and it will all be for not? I don't "need" the truck right away, so might just leave it and figure out what to do? Pretty big let down to say the least.

[sweetk30]

now you say it i see the crack . but it was skimmed over as thats right were STUPID photo bucket put there hosted watermark thing .

[mongocanfly]

That sucks...!!....your friend must have good eyes...I couldn't see it on the small screen...put it up on big screen and zoomed in ...now I see it....