Help! Mercruiser 5.7L Engine knock! Marina mechanic baffled!

[achris]

Re: Help! Mercruiser 5.7L Engine knock! Marina mechanic baffled!

In my novice opinion "I don't think so". The coupler would not be knocking like that unless the bolts were comming loose out of the flywheel. You would not get "ANY" drive out of the prop if the coulper was that loose.

I completely agree. The way the boat accelerated would indicate the coupler was not doing anything wrong. I'm still with the rocker/valve train. I'm thinking broken valve spring...

You (OP) also said in one of your posts that the Mercruiser Thunderbolt system wasn't that good.... POPPYCOCK!!!! One of the very best, if not THE best, marine ignition systems out there. And no way is that an ignition system problem. It is mechanical.

Chris.....

 

[NHGuy]

Re: Help! Mercruiser 5.7L Engine knock! Marina mechanic baffled!

Get him to run the motor on the ground with no coupler, and check for that noise at starboard rear of the motor.

 

[achris]

Re: Help! Mercruiser 5.7L Engine knock! Marina mechanic baffled!

Get him to run the motor on the ground with no coupler, and check for that noise at starboard rear of the motor.

I know what you're looking for... Starter motor, right?

 

[twarner4574]

Re: Help! Mercruiser 5.7L Engine knock! Marina mechanic baffled!

Well, it turns out that the coupler was bad anyway...so now I have a new one. Tech said it was making a bit of a racket while running the engine with the drive off. He ran the engine without the coupler and it was quiet. After putting on the new one, it remained quiet.
However, we then put the muffs on the engine and pulled a couple of spark plugs out of the rear of the motor on the port side. After removing the ignition wire while cranking the engine....water was spitting out of the spark plug holes. So , it looks like the head gasket after all. When we pulled the plugs before cranking, water came out of the threaded stem of the plugs. Strangely, no water in the oil...but that's fine with me. I'll let everyone know how things go after the head gaskets are replaced.

 

[FreeBeeTony]

Re: Help! Mercruiser 5.7L Engine knock! Marina mechanic baffled!

Did he pull the engine to replace the coupler?.......
Just trying to determine if he actually did.......being he now found water in a few cylinders.

 

[alldodge]

Re: Help! Mercruiser 5.7L Engine knock! Marina mechanic baffled!

To late now but wonder if the bolts holding the coupler were just loose. Still don't believe the coupler

 

[achris]

Re: Help! Mercruiser 5.7L Engine knock! Marina mechanic baffled!

Make absolutely sure he re-aligned the engine after the coupler was replaced....

 

[twarner4574]

Re: Help! Mercruiser 5.7L Engine knock! Marina mechanic baffled!

He pulled the motor, but not completely out of the boat. Used a cherry-picker (not a boom hoist/pulley) to lift the motor and move it forward to replace the coupler. The shop performing the service is an auto shop with auto service equipment, though one of their techs ( the one servicing my boat) is experienced with marine engine repair.

 

[CharlieB]

Re: Help! Mercruiser 5.7L Engine knock! Marina mechanic baffled!

A crack in the coupler plate will make noise. But I don't think this is his problem.

Head gasket or more likely the exhaust manifold will put water in the cyls. But I don't think that makes his noise.

While the motor is out or has the heads and exhaust out. Take a look at the exhaust flappers. If you cannot find one.............. it has fallen down the pipe and is laying against the transome plate hole, unable to go any farther. It will lay there until the exhaust flow is fast enough to 'flip' it up and against the transome plate, making quite a racket, AND restricting exhaust flow and causing the poor performance.

Since the outdrive is off take a small flashlight and look. Use a long screwdriver and poke about a little and see the plate laying in there.

Careful manipulation of the remote fingers part picker-upper you can snag the flapper and pull it back up out of the pipe.

 

[twarner4574]

Re: Help! Mercruiser 5.7L Engine knock! Marina mechanic baffled!

He pulled the engine "forward" with a cherry picker to get to it. Work being performed at an auto shop, so no boom hoist or overhead pulley there. Port side head gasket was crap, but since he has to pull the manifold anyway, I'm having him do both the port and starboard sides.

 

[twarner4574]

Re: Help! Mercruiser 5.7L Engine knock! Marina mechanic baffled!

Thanks for the tip! I left a message for him a few min ago to check exactly those things at your suggestion. 8)

 

[twarner4574]

Re: Help! Mercruiser 5.7L Engine knock! Marina mechanic baffled!

unmounted it and pulled it forward with a cherry picker to get at it.

 

[81 Checkmate]

Re: Help! Mercruiser 5.7L Engine knock! Marina mechanic baffled!

twarner.....I think you are getting hooooosed by your mechanic!

For one, you first have to pull the risers/manifolds before removeing the head...... Like said before it could have been a bad riser gasket leaking water into cylinders.

Be sure they align the motor...or you will be replacing the coupler again soon.

Good Luck!

 

[achris]

Re: Help! Mercruiser 5.7L Engine knock! Marina mechanic baffled!

"Pulled the engine forward"... Did he remove the drive? MOST CRITICAL that the drive is removed....

 

[twarner4574]

Re: Help! Mercruiser 5.7L Engine knock! Marina mechanic baffled!

He did pull the risers and manifold first... then the heads. I just did not mention that in my last response. When he pulled the head off, it appeared that someone had tried to fix a problem here previously. There was some kind of goo/sealer under the head. The gaskets on each side were also different colors, indicating previous work. There was also a "chunk" out of the bottom of the port side head. So, I'm off to get a reman head.

 

[frantically relaxing]

Re: Help! Mercruiser 5.7L Engine knock! Marina mechanic baffled!

No water in the oil explains the goo in the oil cap, the water (or steam) was likely entering the valley, with the vapor finding its way under the valve covers via the push rod holes...And you guys who thought the coupler wasn't making the noise, how do you know the coupler-to-flywheel bolts weren't loose? I've had 2 torque converters on cars sound like the engine was trying to push a rod thru the block. In both cases one slightly loose flywheel bolt was the cause. Couplers aren't much different than TC's as far as mounting and function. Also, the coupler spline boss can get extremely worn due to misalignment, to the point the input shaft has plenty of room to rattle around, yet still have enough spline depth left to run the drive...

 

[Bt Doctur]

Re: Help! Mercruiser 5.7L Engine knock! Marina mechanic baffled!

This is useless WITHOUT PICTURES There was also a "chunk" out of the bottom of the port side head. So, I'm off to get a reman head.

 

[CharlieB]

Re: Help! Mercruiser 5.7L Engine knock! Marina mechanic baffled!

While the exhaust is off is a great time to check to be SURE those flappers are in position.

If a flapper has fallen down into the exhaust it will flip around at speed making quite a racket and restrict exhaust flow, reducing power and causing the engine to overheat.

 

[Scott Danforth]

Re: Help! Mercruiser 5.7L Engine knock! Marina mechanic baffled!

unmounted it and pulled it forward with a cherry picker to get at it.

thats all and great, however did he remove the drive first? or did he simply unbolt the engine from the flywheel housing?

in either way, once the engine is mated to flywheel housing, it MUST BE ALIGNED!

now on to your cylinder head issues, we need pics of "a chunk missing"

 

[Wave thumper]

Re: Help! Mercruiser 5.7L Engine knock! Marina mechanic baffled!

Were any of the pushrods bent from running the engine with water in the cylinder?

That engine really sounded like it had a problem with the valve train. Check everything thoroughly before reassembly.