350 MPI running very rough, will not idle, loud tap

[Puma]

Went down to take the boat out today and, after dropping it back in the water, the engine really didn't want to turn over (sounded like a dead battery). I switched to the other battery, and it turned over slowly and then started hard. Would not idle, but would run with the throttle advanced to about 1000 RPMs or so. Loud tapping sound out of one side of the engine. No overheat or anything like that (but only ran it for a min or so). Water was flowing through the engine correctly (I could see it on my flush system check valve).

Last time I ran the boat, it was fine. I ran it off a hose a few weeks ago and everything sounded great (using a Perko flush in the water intake line).

I checked the oil and it looked high to me, but that could just be my imagination.

My guess is that I somehow, when running it on the hose, forced water into the engine and partially hydrolocked it. Please don't let this guess prevent anyone from making suggestions though! Really weird thing is that this seemed to come totally from nowhere, the last time I ran the boat it was perfect (certainly didn't knock like it is now, and ran perfectly on the hose). Also, if this is a hydrolock (and likely something bent/broken in the engine, ugh..) what did I do wrong? Boat was out of the water running at about 700RPMs on the hose for 10-15 mins the last time I ran it (to flush it out). Also, the boat always sits on a lift, so it wasn't reversion while it was sitting or anything like that. Bilge is nice and clean (no oil, no water).

The tapping sound was related to RPMs. Seemed to be mostly on one side of the engines. The manifolds are good (recently checked).

Engine is a 2006 350 MPI, Serial Number OW370643 (If that helps).

Thanks for any help!

 

[HUMPH]

Did you pull the dipstick and check the color of the oil?

 

[dicor]

If the manifold/risers are original and you boat in salt water I would suspect they caused your problem. 6 years is about there life span in salt water from what I've seen. I changed mine last weekend and while inspecting the old ones I cannot see any possible way to measure the internal wall thickness in the manifold you could develop a hole and you would not ever know it I'll be changing them again in 2017.

 

[Puma]

Did you pull the dipstick and check the color of the oil?

I did. Looked like oil (not milky at all). The level did look high, but, again, I can't say 100% that it was (the oil was change <5 hours ago, so it's very very clean).

 

[Puma]

You think that the flush pushed some water through the manifold into the engine? That would make sense. And the noise I'm hearing now is a push rod/lifter/crank (hopefully not crank)?

I thought that the dry joint exhaust (which the 350 Mag has) pretty much fixed the issue of water intrusion through the exhaust system?

If the manifold/risers are original and you boat in salt water I would suspect they caused your problem. 6 years is about there life span in salt water from what I've seen. I changed mine last weekend and while inspecting the old ones I cannot see any possible way to measure the internal wall thickness in the manifold you could develop a hole and you would not ever know it I'll be changing them again in 2017.

 

[ardeprint]

If oil is higher than the last time you replaced your olil, water ingestion is suspect. Oil is not always milky on the dip stick. Try pumping some oil out using a oil extraction pump. If the oil coming out is like a Cappuccino then you have water. What happens is that water sits at the bottom and your dipstick may not reach the bottom of the oil pan. Trust me I learned this the hard way.

 

[BonBini]

You don’t need to run the engine any more to start some trouble shooting.

1)… pull the oil filter, cut it open for inspection. Got metal, got big problems. Looks good, then put on a new one and move on.
2)… pull the sp plugs out for inspection. Look for an odd ball.
3)… pull the suspect valve cover for inspection. Look for valve train out of place. Crank it over with the plugs out and watch things moving if nothing looks wrong right away.

As suggested above you most likely went through a hydro lock.

worse case scenario: hung open an exhaust valve, knocked a push rod off, snapped a piston skirt, now you hear the piston knocking on the bent exhaust valve.

 

[Puma]

Thanks for the help, that's exactly what the plan is for tomorrow.

What's "best case" for a sound like this? Just a bent push rod or damaged rocker arm? Trying to think positive here.

Also, more interestingly, why did this happen? I was flushing the engine as per the instructions (turn the water on a bit, start the engine, then turn the water on all the way). I shut the engine down and then, within 10 seconds, shut the water (on the flush hose) down. Is it really that sensitive? If so, are there any suggestions for a "safer" way to do this. If I wind up having done 1000s of dollars of damage to the engine to try to avoid a 1000 dollar repair (new exhaust manifolds/risers) this will be the last time I ever flush an engine!

If it was a hydrolock, is that usually top end or bottom end damage? I'm hoping for top end because most of that I can do without pulling the engine.

Also, finally, I assume, because the engine would run, that the water is now out of the cylinder(s)?

You don’t need to run the engine any more to start some trouble shooting.

1)… pull the oil filter, cut it open for inspection. Got metal, got big problems. Looks good, then put on a new one and move on.
2)… pull the sp plugs out for inspection. Look for an odd ball.
3)… pull the suspect valve cover for inspection. Look for valve train out of place. Crank it over with the plugs out and watch things moving if nothing looks wrong right away.

As suggested above you most likely went through a hydro lock.

worse case scenario: hung open an exhaust valve, knocked a push rod off, snapped a piston skirt, now you hear the piston knocking on the bent exhaust valve.

 

[dicor]

You think that the flush pushed some water through the manifold into the engine? That would make sense. And the noise I'm hearing now is a push rod/lifter/crank (hopefully not crank)?

I thought that the dry joint exhaust (which the 350 Mag has) pretty much fixed the issue of water intrusion through the exhaust system?

The dry joint system is a big improvement however the way I understand it is that it will help to protect the motor from a failed riser/elbow but not a failed exhaust manifold. Someone correct me if I'm wrong.

 

[ardeprint]

The dry joint system is a big improvement however the way I understand it is that it will help to protect the motor from a failed riser/elbow but not a failed exhaust manifold. Someone correct me if I'm wrong.

This is correct. The exhaust does not fail only at the joints. Yes joints are a weak point, but rust can weaken the metal allowing water to break through the inside of manifolds and elbows through pin holes or cracks.

 

[ardeprint]

My guess is that I somehow, when running it on the hose, forced water into the engine and partially hydrolocked it.

It sounds like you didn't cause the problem. Things like this are usually not the direct result of the actions you mention. Take it step by step. First, change your oil to rule out water in the oil. Look for metal shavings, etc... Check compression!!!!!!
My engine runs rough and makes a thumpy sound when one cylinder is not firing. So, check all your cables, cap and rotor. MAKE SURE YOUR EXHAUST is not leaking water.

 

[BonBini]

Best case scenario: engine cranked slow due to low batt voltage or bad starter. Engine noise due to collapsed lifter from lay-up. But that would be coincidence or just bad luck.


some times to change your luck: walk aroung with your left rear pocked turned inside-out!

 

[Puma]

Best case scenario: engine cranked slow due to low batt voltage or bad starter. Engine noise due to collapsed lifter from lay-up. But that would be coincidence or just bad luck.


some times to change your luck: walk aroung with your left rear pocked turned inside-out!

Mystery solved.

Water in 5&7. Knocked the lifters/rockers out of position and was causing a knock.

Compression is low on these 2 cylinders (110lbs or so), but my mechanic thinks that it's because the valves aren't seating correctly and suggested sending the heads to a machine shop. He's pretty confident that the bottom end is OK. This sound normal (IE, like it's the right course of action to take)? Also, of course, we need to figure out where the water came from and fix that as well, but, does this sound like the right course of action for the engine damage caused by the water entering?

Thanks!

 

[ardeprint]

Mystery solved.

This sound normal (IE, like it's the right course of action to take)? Also, of course, we need to figure out where the water came from and fix that as well, but, does this sound like the right course of action for the engine damage caused by the water entering?

Thanks!

Absolutely...

Regarding the water, when they take the heads out have them check for water jacket leaks. There are a few tests that can be done, am sure someone here with better knowledge can tell you in more detail. IMHO I think your exhaust is where you have the failure. Usually is...

 

[Bucit]

I agree. I can't see how flushing your motor (the way you desribed) would have "pushed" water up into the cylinders. I think you have a different problem that caused this.

 

[Puma]

Yup, it appears the 2 things are just coincidental; the riser just happened to fail when I was flushing the motor.

Does the resolution to the problem seem reasonable? Change the manifolds/risers, and head to a machine shop (to resolve the low compression issue)? Or should I tear the motor all the way down to look for bottom end damage? The mechanic seems pretty confident that the damage is located only in the top end, I just want to make sure that sounds reasonable.

I agree. I can't see how flushing your motor (the way you desribed) would have "pushed" water up into the cylinders. I think you have a different problem that caused this.

 

[Puma]

Also, interestingly..

The mechanic was surprised to find water in the intake manifold. He guessed it was probably from the water that was in the cylinder, it pushed into the intake manifold when the valves let go. Seems logical, I just wondered if anyone had ever seen that before.

 

[mainstream]

I found this thread about flushing engines with muffs I don't know if this pertains to you but found it interesting http://forums.iboats.com/showthread.php?t=44372

 

[BonBini]

Good chance you may have made piston/valve contact (the water rusted up the stem to guide and hung them open). You stated when it was running it had a noise! From the days I worked on gas Truck engines, the exhaust valves were sodium filled. Very brittle and could not take much of a hit. Right now you could have a bent valve or two. With rockers off, laying a straight edged across the top of the valve tappets will show a low one (not coming up all the way closed). I would definatly pull the head and have the valves reworked. Do not re-use any that have been hit.

 

[Puma]

That's exactly what the mechanic suggested (and what I'm doing). The heads are on their way to a machine shop for a full valve job.

I'm more concerned with possible lower end damage (bent connecting rod, etc). My mechanic seems pretty confident it's only upper end damage, and we got the heads off <2 days after this happened, so the pistons look pretty good (a little rust, but nothing at all severe), so he thinks we can get away with just the heads/valves and exhaust. I'm still a little concerned with the lower end, but he told me it's pretty unusual for water intrusion to actually grenade a rod or crank; the valves are much weaker and usually give way long before those components.

That sound reasonable?

Good chance you may have made piston/valve contact (the water rusted up the stem to guide and hung them open). You stated when it was running it had a noise! From the days I worked on gas Truck engines, the exhaust valves were sodium filled. Very brittle and could not take much of a hit. Right now you could have a bent valve or two. With rockers off, laying a straight edged across the top of the valve tappets will show a low one (not coming up all the way closed). I would definatly pull the head and have the valves reworked. Do not re-use any that have been hit.