Thread: 5.7 Heads replaced now low compression-Help !

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Hello Everyone,
So I have a 2002 5.7, replaced both of my heads since they were cracked (as per machine shop). Heads are new aftermarket heads. After adjusting rocker arms with a technique that had me spinning the motor sever times. The engine wouldnt start and noticed I had no compression.

I Loosened all rockers and tried another valve lash adjusting technique. My compression reading went up but most under 100. I backed off the rocker nut all the way loose on the rocker arm so there would be no pressure on the valves. cylinder compression are 110,120,90,100,70,40,30,80. This is still extremely low. The engine pistons and rings look fine when I removed the heads.

What is going on wrong. Please help/advise
Sincerely,
Fred

Welcome to the site.. and your very first question is a doozy! I'm just going to shoot from the hip and toss out ideas. the biggest is because you don't say who's heads.. only aftermarket.
Edelbrocks I'd probably trust right out of the box and a few others.. if you got these from ebay or similar, I'd say send them to a shop that does valve work and have them inspect before even installing.

And your results so far warrant that imho. Also, are you certain the head gaskets were installed correctly? They should've been marked to show top front or some such. If you are correct and the cylinders looked good, then the valves or gaskets are not sealing...

Welcome, Fred. I think Mike/34_40 is on the right track, but your post raised questions for me. Has your 20 year old engine been rebuilt, or just new heads? How did you assess the pistons & rings being "fine"?

I posted a link about adjusting rockers a few days ago, and I believe it's a foolproof method, for what it's worth - Big block rockers

Thanks for your inputs. The heads were puchased from a cylinder head company out of Florida that specializes in aftermarket Heads. The engine is actually on my boat. It had been rebuilt just a year and a half ago. Unfortunately there was a fire on the boat and the harbor fire extinguished flames with a fire hose. Most likely why I got water in my engine oil.

Thats why I ended up changing the heads.

I just spoke to a marine mechanic and he said it maybe possible the rings are stuck. Due to having water in the engine from it being extinguished by a fire hose. Then I was not allowed to touch the boat what so ever for all investigations to be conducted including sheriff and insurance. That took almost 1 year! I was informed to put motor oil in cylinders. Any other thought or advise is greatly appreciated.
Fred

Originally Posted by fgil

I just spoke to a marine mechanic and he said it maybe possible the rings are stuck....
Fred

What did your marine mechanic advise? If you're confident that your heads are good and the head gaskets are right you might try getting a quart of Marvel Mystery Oil and putting a few ounces in each cylinder and let it soak overnight, then crank it over with the plugs out so you don't hydraulic the engine. Then I'd set the rockers using the zero lash method, bring it to #1 TDC and be sure your distributor is in right. Even with some cylinders at low compression it should fire if you're getting air, fuel and spark. If you get it to fire set your timing, then bring it up to temp and cycle the rpm's without getting crazy and see if it improves. Then check your compression again.

Thanks and great advise. Forgot about Marvel Mystery oil.

I added Marvells Mystery oil and the compression went up. Some cylinders were still under 100 but most over. Im letting the low cylinders soak a little longer and check in a few days. Just sharing my results, crossing my fingers the compression stays up.

So heres the latest. All cylinders are over 120 but three remain below 70. Any suggestions before I decide to yank the motor out and replace it?
Thanks
Fred

Pull the heads and inspect the gaskets.

Originally Posted by fgil

So heres the latest. All cylinders are over 120 but three remain below 70. Any suggestions before I decide to yank the motor out and replace it?
Thanks
Fred

Did you start it and bring it up to temp, or just crank it for the compression test after the oil soak. I expect Mike's right on checking gaskets, but it'll start with 5 of 8 above 120#, and if anything's gonna free up the rings on the other three it's running it and getting it hot.

Another thought, since this happened from a fire, perhaps due to the method used to extinguish the fire, will insurance pay for replacing the engine?

Never started the engine. Just turned it over to check compression.