Mercruiser 350 Mag MPI engine noise

[sfitr]

After waiting the whole winter, the boating season finally arrived ! I went out with my boat for the first time this season for a short trip, everything worked well, a couple of beers and headed back home. As I left I noticed a load clanking noise just above 2K RPM which seems it came from the rear part of the engine. I immediately thought it was a gear / drive problem. I pulled to neutral. Forward and reverse engaged perfectly and engine revved perfectly to over 4K RPM without any noise at all. Oil levels of both drive and engine where ok. I decided to drive home slowly with the engine revving 1.5K (10mph) no noise at all.

The following morning my mechanic came to inspect the boat and he said it could either be a weared U Joint from the Bravo 3 drive or also the engine coupler / damper. I pulled the boat out of the water, and he removed the drive. inspected the gymbal bearing and even the U Joints seemed ok and he said its the engine damper. In short, I bought a new and changed it, launched the boat again and guess what ? ! the same clanking noise over 2k RPM came again. Unfortunately I had to pull her up again, after spending around ?1k and the problem wasn't solved. He said that it might be an upper bearing from the Bravo 3, but when it was dismantled everything seemed as new ! What else could it be ? A lower part problem from the drive ?

The engine is a 2004 Mercruiser 350 Mag MPI Bravo 3 with less than 400 hours of pleasure cruising on a 2004 Crownline 270 CR cruiser.

 

[alldodge]

Sounds like you have some of the same kind of "mechanics" that we have over on our side of the pond. This guy likes to throw parts at the problem hoping he guesses correctly, and its not his money. Sure hope you kept your old parts, there worth something.

Sounds are hard to spell out on line, is their a way to record the sound and post?

I don't think its in the drive. Does the sound go away it rpms are increased or does it get louder?

 

[JonBrown]

With the drive off... And a hose/water running through the engine .. Bring it to 2000 RPM and see if the problem is the engine or component. Water pump/alternator etc.. Or even engine itself. After you eliminate the engine you can start from flywheel back. in 2 more stages. Lower unit removed and gearbox installed..etc. Do not run it long just a quick test with water flowing. A closed system you may not require a hose although recommended. My 2.5 cents worth.
jon

 

[sfitr]

Sounds like you have some of the same kind of "mechanics" that we have over on our side of the pond. This guy likes to throw parts at the problem hoping he guesses correctly, and its not his money. Sure hope you kept your old parts, there worth something.

Sounds are hard to spell out on line, is their a way to record the sound and post?

I don't think its in the drive. Does the sound go away it rpms are increased or does it get louder?

The sound does get a bit louder as the rpms are increased. I will try to record and post the sound, only if it also happens while the boat is ashore with hose connected, as I got a feeling that it only does it under load only.

 

[sfitr]

With the drive off... And a hose/water running through the engine .. Bring it to 2000 RPM and see if the problem is the engine or component. Water pump/alternator etc.. Or even engine itself. After you eliminate the engine you can start from flywheel back. in 2 more stages. Lower unit removed and gearbox installed..etc. Do not run it long just a quick test with water flowing. A closed system you may not require a hose although recommended. My 2.5 cents worth.
jon

Revving the engine on idle to over 4.5k rpms does not make any sound at all. I have a feeling that its only doing this under load. The upper and lower part of the drive were dismantled today... Everything seems perfect according to the mechanic, not even a single piece of glitter, oil as as new.

Someone told me it could be the crank pulley ? But my mind says that if its it, it should do the noise even when revving on idle.

 

[Fun Times]

Then be sure to grab the crank pulley and try pushing/pulling it to ensure it don't move.

Has he had a chance to inspect the engine coupler and alignment yet...Just in case you/he needs to thoroughly dig into the engine coupler area by pulling the engine, etc., here is the latest installation info he may not be fully aware of the, Coupler-installation change http://www.marinemechanic.com/merc/...d/New Folder/coupler-install-change_EN_11.pdf

 

[sfitr]

Then be sure to grab the crank pulley and try pushing/pulling it to ensure it don't move.

Has he had a chance to inspect the engine coupler and alignment yet...Just in case you/he needs to thoroughly dig into the engine coupler area by pulling the engine, etc., here is the latest installation info he may not be fully aware of the, Coupler-installation change http://www.marinemechanic.com/merc/...d/New Folder/coupler-install-change_EN_11.pdf

Coupler was replaced with a new one as the "mechanic" thought that it was the culprit ! But he was so wrong ! The clanking noise is still there. I will tell him to inspect the crank pulley, though I heard its very uncommon to break on a pleasure cruiser.

 

[JonBrown]

As Alldodge had said earlier. Most mechanics will start throwing parts at it. So you need to be a bit involved with the mechanic to be sure he has a open mind on the problem. If it is doing this under load , does it do it in reverse as well? I am sure you will not do 2000 rpm in reverse although you have to eliminate engine and or out-drive. Very few things on a engine would have a sound under load except for the flex plate or flywheel. And alignment is crucial. Then followed to the universal and of course the bearing . Since you are hunting a ghost problem being creative to locate the area shouldn't have anything to do with buying parts. I am always afraid I will make another problem by guessing at the first problem. Something that has happened in my younger days...

 

[Bob79]

A check of the timing and a compression test maybe worth a try. Quick and easy to rule out and major engine problems.

 

[sfitr]

A check of the timing and a compression test maybe worth a try. Quick and easy to rule out and major engine problems.

This is going to be tested next Monday. But I really have my doubts on this as the engine fires up perfectly, idles like new and revs up to over 4.5k without any abnormal noises at all Anyone can suggest anything else to check ?

 

[alldodge]

Would sure like to hear what your hearing

 

[sfitr]

Things got a bit clear yesterday, a compression test yielded cylinder 2 with very little to none compression ! Plug of the same cylinder was soaked with petrol. Mechanic is now putting the blame on a blown head gasket. Heads are going to be dismantled today. If it's a blown head gasket I now have to determine the reason behind it ! The boat never overheated since I owned it for 4 years and I also don't remember revving it hard either.

 

[Fun Times]

Sorry to hear that! Hope it's not to severe of a problem for you.

Just some thoughts to start off with,
Was the two low cylinders right next to each other?
Probably to late to check now but was engine timing checked to ensure it was right on specifications. And be sure those two cylinder plug wires are firing since they were wet with fuel.
Did it seems to be running rich at all.
What brand/part number spark plugs where installed.

 

[sfitr]

An update following my previous post. Head gasket was blown on one head and on the other was almost blown. Mechanic is saying that it seems that the engine once was overheated. Maybe it did overheat while it belonged to it's previous owner, as for the 3 years I owned it, it never did. Timing was never messed with either.
So now both heads where re surfaced and new head gaskets were installed, mounted them and started the engine. After running for around 10 mins at low rpms with hose attached to outdrive, temperature went up to over 180 and alarm sounded. Water was also coming really hot from the exhaust from out drive.
Mechanic tried to remove thermostat to help water circulation but it didn't help at all. We tried to rev the engine to 2k rpm also didn't help either.
So why is my engine overheating? Mechanic told me that the block might needed re surfacing also, and head gasket blew again! Is this possible?

 

[alldodge]

That word "mechanic" sure gets used a lot and there appear to not be that many of them around. Someone removes the heads, finds they need to be resurfaced and does not check flatness on the block. This is not done before they put the heads back on or even before any work is started on the heads.

Now to add insult to the issue, the motor over heats and the thermostat is removed to try and clear. The thermostat is needed to keep the block full of water, without it, there can be air pockets. I wonder if he ever tried to remove hoses and back flush the cooler, or anything before even looking at the thermostat.

The head gasket can blow again "IF" the block is warped, if the head was warped and not resurfaced, and if the head was not torqued correctly, and if someone used anything but the head gasket, no head gasket sealer is allowed.