Merc 5.7EFI Issues

Strecker25

Well-Known Member
SILVER Sponsor
Nov 20, 2014
4,905
Rochester, NY
Boat Info
2002 410DA
Engines
Caterpillar 350HP 3126
Well this is a follow up to my other thread thinking it was a spun prop hub. It's not. I know you can't diagnose this over a keyboard either, just looking for thoughts.

The history is I took the boat on the first ride of the year, all was fine cruising at 3k RPM when I heard a very fast ratcheting/ticking/clicking sound. I backed off immediately, motors never stalled. It only happens when powering up or on plane.

Put the new prop hub in today and went out. The starboard motor starts normal and idles ok, but has more vibration than the port. When is start to power up it makes what I'd consider a ticking or clicking sound, more pronounced under load.

If it wasn't for the original noise I'd think maybe down a cylinder or bad plug/wires/cap but given that pretty loud initial noise I have to assume something worse. Dropped a valve? I would think if it was in the bottom end it would be a noticeable sound even at idle.

Another symptom were some air bubbles on the oil on the dipstick. Normal oil level and pressure, not milky at all.

Not even sure where to start honestly. Might pull the plugs and take a look and even replace plugs/cap/rotor/wires but Im not hopeful
 
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Drives off every year, alignment checked and good. Gimbal 4 years old but checked yearly. Coupler greased twice a year.

I hear noises from the area of 2/4/6 Cylinders.

I’m going to check compression as a starting point tomorrow, maybe that will tell a story
 
It may have been mentioned before, but don’t forget the basics.

I had an issue 2 years ago, wouldn’t hit WOT rpm, loss of power on the higher rpms, and a rapid metallic-like tapping/banging sound.

The higher the load, the more likely for it to happen.

I replaced the cap and rotor and it resolved the problem. (It was the original cap with 10 years and 300 hours on it)
 
Oil filters are cheap. It may not be a bad idea to open it up to look for an indication of an internal failure. It could prevent further damage from running if that is the case.
You could also remove the valve cover on that side of the engine and check for unusual amount of clearance in the valve train. You will want to check that in several positions over 2 revolutions of the crankshaft.
If all checks out and since the noise is more apparent toward the front of the engine, you could try running with the belt(s) off to see if that changes anything.
 
Thanks all. I took a breath and thought of what I can do troubleshoot. Pulled the plugs cap and rotor today. Cylinder 4 is clearly down, take a look at this plug. It’s on the right, cylinder 2 is on the left. There is black oil/sludge on the bad plug.

Compression check and borescope is next.

F9A15283-1C0A-439B-AEB1-D412FBBB990A.jpeg
 
Well, she’s out to get the motor pulled. That cylinder is dead. I have to assume i tuliped the valve and that was the awful tapping noise I heard initially.

Well know more in a couple days when they tear into it.
 
749

interestingly enough, that engine always reports slightly higher iron in the annual oil analysis. With any luck its a top end job but the motor is coming out anyways so we'll see. I may just rebuild them both
 
Verdict is in, blown head gasket. They think it may have overheated at some point, but No major physical damage to any rotating or moving parts. Bad news is the deck is pretty well scored. The shop owner and head builder is looking at it tomorrow and I’ll also swing by to get a look. We’ll make a decision on whether to deck it or just get a new block. Everything will get dipped and reassembled, put on the dyno, and dropped back in the boat hopefully soon

I was going to tear down the other motor and freshen it up at the same time but I think we’ll put that project off until the winter now. I am going to go to the yard to really clean that side of the bilge though.
 
Went today to look at the old block and head. Big hole between 4&6, he wasn’t kidding about pencil sized.

The question now is what the hell caused this. He suggested we drain the rest of the tank (30 gallons) and start with fresh fuel.

The manifolds and risers are only a couple years old and there are no signs of any water leakage causing it.

Something wonky in the ignition system causing pre-detonation?

I hadn’t changed the fuel filters yet, lean condition?
 
Went today to look at the old block and head. Big hole between 4&6, he wasn’t kidding about pencil sized.

The question now is what the hell caused this. He suggested we drain the rest of the tank (30 gallons) and start with fresh fuel.

The manifolds and risers are only a couple years old and there are no signs of any water leakage causing it.

Something wonky in the ignition system causing pre-detonation?

I hadn’t changed the fuel filters yet, lean condition?
Who is doing the engine work? Tim Mangus did mine and it was Dynoed at Ontario Offshore Performance
 
Martin engine machine in Webster, it’ll be dyno’d At offshore as well.
 
on the dyno now, timing was not advancing which is probably what killed the motor. Putting a new distributor in it to get it tuned and tested now.
 
New distributor, cap rotor, wires, and coil and she’s all sorted out. Should go back in the boat next week.

 
Here’s the final product. Having an issue with idle random stalls and not iac but we’ll chase that down. Purrs right along now

 

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