Head Gasket between cylinders Knocking?

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sbump

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Good Evening. I was driving home a few days ago and had a sudden loss of power and a rattle/ knock noise with engine load. After a compression check I found cylinder 3&5 at 0psi. I pulled the head and found a blown head gasket between 3&5. Unfortunately both heads are cracked. My question is for someone who has failed a head gasket between cylinders. Did your engine make a knock/ rattle noise? My concern is now that I am into it if I could have had a rod bearing knock or something’s else causing that noise. I am not familiar enough with it to know if a failed gasket between cylinders can make a knock noise or if I should investigate further. The engine has 150,000 on it. I never had low oil pressure. I drained the oil and it did not appear to have water or noticeable wear metals. I mainly trying to add up if the noise matches my findings before investing in new heads.

thanks
 

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GoToGuy

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The most likely scenario is when you feed in throttle with blown gasket between mating cylinders the compression, ignition, exhaust cycle is all screwed up and that power imbalance caused a knocking sound.
You pulled both heads ? Both heads have cracks?
 

sbump

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The most likely scenario is when you feed in throttle with blown gasket between mating cylinders the compression, ignition, exhaust cycle is all screwed up and that power imbalance caused a knocking sound.
You pulled both heads ? Both heads have cracks?
Yes Both heads were almost identical. The gasket was on its way out between 4&6. Both had cracks on center most head stud location and few valve seat cracks. It has been down in power for a little while but is mostly used as a ranch truck. I hauled it home the other day for an oil change and basic maintenance. I took it for a drive to work the other day just to test it before hauling back out to the ranch and had my issue. I have never gotten it hot but I can’t say for the 125,000 miles before I owned it.
 

dave s

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That's a tough call. If it's a ranch truck I'd do a good visual on the cylinder walls and if what you can see of the pistons look to be good shape I would probably put a set of heads on it, reassemble everything and run it. It reads like you are doing the job. Might be cheapest way out.
If money is no object, drop a fresh GM crate motor in there!
 

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Ok since you got the heads off. Turn the engine over until the pistons reach TDC on the cylinders in question. After the piston starts to go down a bit, stop and then push down on that piston. If it goes down more, the upper rod bearing is toast. For the lower bearing the piston must be going up, stop, then reverse crank rotation back down some, again push down on piston.

Still not entirely a perfect method to check since the bearing needs to be pretty toast, if I got it right LOL the up/down always gets me mixed up.
 
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sbump

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Ok since you got the heads off. Turn the engine over until the pistons reach TDC on the cylinders in question. After the piston starts to go down a bit, stop and then push down on that piston. If it goes down more, the upper rod beating is toast. For the lower bearing the piston must be going up, stop, then reverse crank rotation back down some, again push down on piston.

Still not entirely a perfect method to check since the bearing needs to be pretty toast, if I got it right LOL the up/down always gets me mixed up.
Thank you. I did do this check yesterday and did not find anything that stood out. Based on similar noise feedback above I feel good about replacing heads.
 

Schurkey

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I put a Service Replacement L05 Caprice engine in my K1500 back around 1998-1999, something like that. The L05 passenger-car engine has a roller cam, flat-top pistons but is otherwise similar to the L05 truck engine.

About 18 years, and ~80,000 miles later, the thing sounds like it has a rod-knock when I'm going to get Subway for supper. Very throttle-dependent. At light throttle, the knock went away (at first.) Loud as hell when accelerating.

By the time I got back from Subway, the knock was constant and constantly loud. No power. Wasn't sure I'd get home until I pulled into the driveway.

Head gasket blown between 3 and 5; the blowtorch effect of the combustion gasses gouged the block and the head. I might be able to salvage the block; but it'll take quite a cut on the milling machine to do so. There's no hope for that head. It's bolted to the back of my riding lawnmower to counterbalance the snow-blower attachment during the winter.
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I rebuilt a Vortec 5.7L short-block and put aftermarket cylinder heads on it.




1--8--4--3--6--5--7--2
Each cylinder is 90 degrees away from it's neighbor in the firing order.
#3 and #5 are 180 degrees apart.

Keep in mind that when #3 fires, #5 is getting toward the end of the intake stroke. #5 has nearly a full charge of fuel/air. The #5 cylinder is ignited by the #3 flame crossing the opening where the head gasket has failed. The #5 piston is near the bottom of it's stroke. Not only does the pressure spike on #5 try to turn the crank backwards while #3 is turning it the correct direction, it's very likely to ignite the fuel/air in the intake manifold too, because the #5 intake valve hasn't closed yet. If the intake manifold fuel/air ignites, #7 and #2 could get a contaminated air/fuel charge.

Yeah, the engine will have no power.
 
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