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Help to identify 5.7 noise

Bt Doctur said:
A cracked piston should also have a dead cylinder, I detect to mis-fire or shaking
Click to expand...

If piston is slightly cracked near pin, that play in pin area could make noise, but not loose compression. That's what last mechanic told. ?
I'm going to the boat today to investigate deeper Your mentioned possibilities. Any ideas how to check these, You mentioned?
Thanks
 
Step 1. Remove valve covers, inspect rocker arms and see if any are extremely loose as compared to the rest or broken or not sitting on the valve or push rod. If they all look ok then see if ALL rocker arms are moving and are moving about the exact same amount with engine idling. There will be oil running down so have a lot of rags and KEEP YOUR HANDS OUT OF/AWAY FROM THE MOVING PARTS
If any are not then that will be your issue.

If all looks good on the rocker arm assembly then the issue may be within the engine deeper then there is no way to tell exactly without removal and disassembly.

Everything else is just a guess.

You are looking for an answer to a YOUTUBE video from the internet vs being there and listening to it first hand with a stethoscope to try to pinpoint the sound.

Also what is the history on this engine?

Has it ever overheated?
Is it original or a rebuilt?
WHat other issues if any have you had that were mechanical in nature?

Trying to pinpoint a possible cracked piston from a video and the sound is 1000% impossible.

You could have spun a bearing on a connection rod, you could simply have a failed piston slapping the cylinder walls, or a number of other issues.......


Only way to tell once the valve train has been eliminated it to pull it out of boat and pull it apart........
 
While the engine is running and making the noise, disconnect one plug wire at a time to see if the noise stops. If it doesn't, reconnect the wire and repeat for the next cylinder. A cracked piston or bearing noise should be much louder when the cylinder is firing. A valve train noise should be the same whether the cylinder is firing or not.
 
bobbyc said:
While the engine is running and making the noise, disconnect one plug wire at a time to see if the noise stops. If it doesn't, reconnect the wire and repeat for the next cylinder. A cracked piston or bearing noise should be much louder when the cylinder is firing. A valve train noise should be the same whether the cylinder is firing or not.
Click to expand...

If he does this he will get hit with 30,000 volts....................

There are better ways to short out a spark plug wire so not to fire the spark plug..........
 
bobbyc said:
While the engine is running and making the noise, disconnect one plug wire at a time to see if the noise stops. If it doesn't, reconnect the wire and repeat for the next cylinder. A cracked piston or bearing noise should be much louder when the cylinder is firing. A valve train noise should be the same whether the cylinder is firing or not.
Click to expand...


Tried that today, no change in noise when disconnecting wires.
 
kghost said:
Step 1. Remove valve covers, inspect rocker arms and see if any are extremely loose as compared to the rest or broken or not sitting on the valve or push rod. If they all look ok then see if ALL rocker arms are moving and are moving about the exact same amount with engine idling. There will be oil running down so have a lot of rags and KEEP YOUR HANDS OUT OF/AWAY FROM THE MOVING PARTS
If any are not then that will be your issue.

If all looks good on the rocker arm assembly then the issue may be within the engine deeper then there is no way to tell exactly without removal and disassembly.

Everything else is just a guess.

You are looking for an answer to a YOUTUBE video from the internet vs being there and listening to it first hand with a stethoscope to try to pinpoint the sound.

Also what is the history on this engine?

Has it ever overheated?
Is it original or a rebuilt?
WHat other issues if any have you had that were mechanical in nature?

Trying to pinpoint a possible cracked piston from a video and the sound is 1000% impossible.

You could have spun a bearing on a connection rod, you could simply have a failed piston slapping the cylinder walls, or a number of other issues.......

Only way to tell once the valve train has been eliminated it to pull it out of boat and pull it apart........
Click to expand...

Thanks for taking Your time.
Took out valve covers, all assembly seems ok, didn't run the engine, because exhaust elbow was already removed.
The only thing I didn't like is that white/grey mess, which indicates water. I've noticed that earlier, and thought it's condensate, cause oil on the dipstick, stays where it was. (a bit too much, but stable). Now I've noticed, that water canal on the head is a quite heavily rusty, and possibly gasket doesn't hold there well. I don't know if some water gets into cylinders via intake, could that be related to noise?
History of the engine is not bright. I've bought it as rebuild, but as later figured out- poorly.
The problems I had with it was constantly braking valve springs, and of course bending valves. So I changed all springs recently (old springs had deep rust), did valve job.
I'm planning to tear this engine till last screw and rebuild it with care this winter, but now I have one more month to enjoy.
 
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""The only thing I didn't like is that white/grey mess, which indicates water. I've noticed that earlier, and thought it's condensate, cause oil on the dipstick, stays where it was. (a bit too much, but stable). Now I've noticed, that water canal on the head is a quite heavily rusty, and possibly gasket doesn't hold there well. I don't know if some water gets into cylinders via intake, could that be related to noise?""


""History of the engine is not bright. I've bought it as rebuild, but as later figured out- poorly.
The problems I had with it was constantly braking valve springs, and of course bending valves. So I changed all springs recently (old springs had deep rust), did valve job.""

Just looking at the valve train is not good enough. The engine has to be running so you can hear and SEE what is going on.......

Water does not just happen to get into the head area around the springs and rockers arms......Some moisture is present after sitting for a while but typically evaporates when under use.

If there has been water running thru the engine on a regular basis most likely there is some kind of rod or crank bearing issue. Especially if this is in a salt water environment. Unless you run engine and watch and listen with valve covers off, first.
 
kghost said:
Just looking at the valve train is not good enough. The engine has to be running so you can hear and SEE what is going on.......

Water does not just happen to get into the head area around the springs and rockers arms......Some moisture is present after sitting for a while but typically evaporates when under use.

If there has been water running thru the engine on a regular basis most likely there is some kind of rod or crank bearing issue. Especially if this is in a salt water environment. Unless you run engine and watch and listen with valve covers off, first.
Click to expand...

Water was this season only, since I've noticed I ran engine totally of 4 hours usually at idle and one hour at 1200rpm. Fresh water. Shouldn't be lots of damage because of that. BUT, sound was the same last season, when no water was present.
Ok, so now I will disassemble and clean lifters, assemble everything back, except valve covers, and start the engine.


P.S.: Maybe You know magic way how to put valve cover on, while elbow is on already?
 
You have a water leak somewhere

could be a cracked head.

did one two summers ago, center head bolt on one head the casting under the bolt, head was cracked (inside head casting) and water was a slow drip into valve spring/rocker arm area..............purchased used heads and had a quick cleaning and some minor work and all was good......

Unfortunately no way around loosening manifold and getting valve cover off. You dont have to remove, only loosen.

Also make some cardboard pieces and stick them into heads very near manifolds to try to keep oil in head area to minimize clean up.
 
Hello again,
update after some time. Only now had time to disassemble engine. Sent to workshop and they found that block is cracked inside cylinder. They told they could fix it. I don't know if that could be related with sound.
Other than that, everything looks very clean on the engine. Bearings in good shape, can't see any cracks on pistons.

Now I'm thinking to fix the block and reassemble engine.

Here comes the question: what is the difference between 5.7 and 6.2 engines?
Prehistory is that I've bought boat with frost damaged 5.7 engine. Than bought 6.2 used engine, and put it in the boat. (I've noticed, that on the block it says 5.7 also, but checked serial number and it tells, that it's 6.2) I would like to use heads from the old engine (because they are redone in machine shop), they look identical visually, do they have any technical differences?
 
...."I have reverted it back from MPI to carburetor. "


Smart move! A 6.2 is a 350 with a longer stroke. Hot rodders love them and so would you.

Good luck!

Jeff
 
Throw all of the iron in the dumpster and get a reman long block from Merc while they are still available. Repairing a block is never a good Idea.
After you repair and rebuild your damaged block, would you feel comfortable running it down the bay at WOT for 10 miles?

The GM Based 6.2 was not a very good boat engine.
 
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