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

[twarner4574]

Hi all. I am a new boater (since May) and have had some minor typical issues with my 1986 Wellcraft Nova 23. I've had to replace the U-joints, and immediately after my Binnacle shifter. After all that was done successfully, I took a nice enjoyable test ride to make sure all was well. When I came about to traverse the water back to my marina, a horrible engine knock appeared out of the blue. Would not happen at idle, only under load at about 2000 to 2500 rpm. I thought it might be a spark knock or something, However, the Marina mechanic has replaced my spark plugs and distributor cap, as well as adjusted the timing. He said at 6 degrees, it was "off". The thing runs horrible now, and is still knocking under load. When revving the engine at the dock, it's slow and rough before gaining rpm's, but no knock. Only under load. I found a youtube video of someone having the same issue, and they had posted that it ended up being their head gasket. ??? I am posting the link to my video from yesterday for viewing to aid in helping others help me possibly determine what the issue here really is. I've got about 4, maybe 5 weeks of boating season left guys. I can use all the help I can get.
Thanks.:facepalm:

Here's my vid: https://www.youtube.com/watch?v=6uoXGAmAQdI&feature=youtube_gdata_player

 

[Josh P]

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

Sounds like upper end noise. You may have rocker arm issues. check Compression on all cylinders then go from there.

 

[Bondo]

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

Hi all. I am a new boater (since May) and have had some minor typical issues with my 1986 Wellcraft Nova 23. I've had to replace the U-joints, and immediately after my Binnacle shifter. After all that was done successfully, I took a nice enjoyable test ride to make sure all was well. When I came about to traverse the water back to my marina, a horrible engine knock appeared out of the blue. Would not happen at idle, only under load at about 2000 to 2500 rpm. I thought it might be a spark knock or something, However, the Marina mechanic has replaced my spark plugs and distributor cap, as well as adjusted the timing. He said at 6 degrees, it was "off". The thing runs horrible now, and is still knocking under load. When revving the engine at the dock, it's slow and rough before gaining rpm's, but no knock. Only under load. I found a youtube video of someone having the same issue, and they had posted that it ended up being their head gasket. ??? I am posting the link to my video from yesterday for viewing to aid in helping others help me possibly determine what the issue here really is. I've got about 4, maybe 5 weeks of boating season left guys. I can use all the help I can get.
Thanks.:facepalm:

Here's my vid: https://www.youtube.com/watch?v=6uoXGAmAQdI&feature=youtube_gdata_player

Ayuh,... Welcome Aboard,.... Has this Mechanic seen it since the knock started,..??

A compression test will probably point out the problem area,...

Continuin' to run it will lead to needin' a new motor,...

 

[81 Checkmate]

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

Ditto^^^^^^^^^^^^^^ Sounds like top end noise!

Do not keep running it till you find the problem......or..your gona need a new motor!

 

[twarner4574]

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

Ayuh,... Welcome Aboard,.... Has this Mechanic seen it since the knock started,..??

A compression test will probably point out the problem area,...

Continuin' to run it will lead to needin' a new motor,...

Hey there! Compression test indicated all compression was within range. No water in oil pan, but white oily residue on valve cover oil cap which is on the opposite side of where the engine noise is. ??

 

[Silvertip]

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

What does the oil pressure gauge read at 2000 rpm under load. Gauges are there for a reason and the numbers help us since we can't see or hear your engine. Is the noise high in the engine or low in the engine. A metallic clicking, ticking, high on the engine would tend to point to a valve train issue. A deep metallic knock down low on the engine would indicate a crankshaft, rod or main bearing, or piston issue (broken or collapsed skirt, etc).

 

[twarner4574]

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

The oil pressure gauge reads about 30 to 40 psi. The noise is high in the engine on the top right rear. It's a hard knock under load. Watch the video here:https://www.youtube.com/watch?v=6uoX...e_gdata_player
A compression test revealed that all cylinders are within range. New Distributor cap and rotor as well as spark plugs were installed.
I was told that due to the rough running at idle, the thunderbolt ignition box might be bad as well. (heard they never worked well anyway)
Another boater posted on youtube that had the same issue. It sounds identical to mine. He said his problem ended up being a blown head gasket. My oil in the pan is clean as a whistle, but the oil cap on the opposite side of the motor had a milky coffee like looking residue on it. Check out this other guys video too. Sounds identical to my problem. https://www.youtube.com/watch?v=HRyOwnhQwgE
Let me know what you think. Thanks!

 

[FreeBeeTony]

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

Are you loosing a cylinder in this condition? You may have good compression but are loosing a cylinder at higher RPM's......try disconnecting a plug wire while knock is present........it may point you in the right direction.

 

[jthor3277]

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

Sounds like a loose rocker arm to me! That's the push rod with no lash. Find #1 TDC and adjust the intake and exhaust valve nuts on the applicable cylinders. I used to remember the sequence. Here's a youtube link of the procedure. http://www.youtube.com/watch?v=89o5rLpbCgI

 

[81 Checkmate]

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

twarner...here is what id do. You say it sounds like the its coming from the top port side.........Take that valve cover off and have a look.
Could be a loose rocker, bent pushrod, or a rocker stud backing off.

If it was a blown head gasket it would run like crap all the time.... Low compresion in that area....
If it was the ignition system it wouldn't rev or get on plane.....Check it with a timming light and see if it is advancing.

Or take it to the mechanic and have him look at it.

 

[twarner4574]

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

Well, I took it to the mechanic...the same one who did the compression tests, etc. As soon as he removed the oil cap and saw the heavy coffee tinted cream on the inside of the cap....he said.." Yup. Time to REPLACE the motor". Ugh! :facepalm:

 

[FreeBeeTony]

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

That's a pretty fast diagnosis wih a pretty $$$ repair........I wouldn't jump so fast.

 

[Bondo]

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

Well, I took it to the mechanic...the same one who did the compression tests, etc. As soon as he removed the oil cap and saw the heavy coffee tinted cream on the inside of the cap....he said.." Yup. Time to REPLACE the motor". Ugh! :facepalm:

Ayuh,... You need to find a Mechanic that can Diagnose the issue, rather than callin' it a Dead motor,....

Just because there's Condensation in the valve covers,...

 

[Bt Doctur]

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

possable loose rocker arm( pull the valve covers and watch the valve train) , severe detonation(check spark plug color), or a cracked flywheel dust cover(hand inspection if metal)

 

[twarner4574]

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

Hey Doc. I decided to spend a few bucks on having a different tech open up the motor and have a look inside (rockers,etc). I'd rather do that than replace the freakin' motor! I'll keep everyone posted on what he ends up finding. It's always good to share the wealth of knowledge. 8)

 

[3riverscapri]

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

Did you ever get any answers on this? We bought our '99 Capri 3 weeks ago and are having what seems like the exact same issue.

 

[Bondo]

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

Did you ever get any answers on this? We bought our '99 Capri 3 weeks ago and are having what seems like the exact same issue.

Ayuh,.... Welcome Aboard,.... So start a thread of yer own, 'n tell Us 'bout it,....

Don't forget the motor, 'n drive serial numbers,....

 

[twarner4574]

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

Hey there 3Rivers. The tech I had look at it performed a compression test of his own on all cylinders and all were within range. He wanted to rule out the other guys incompetence, and so he did. He then decided to run the motor with the outdrive/lower end off of the motor. When he did, he heard a hell of a clanking. What he found was that the engine coupler had given out. It's possible this happened due to the engine either being misaligned, or having somehow come out of alignment. At any rate, he just found the problem today. I went to get the part, and of course nobody has one. Slim chance that my boat will be ready for the Labor Day holiday. 8( I'm sorry to hear about the issue you are having with your 3 week old '99 Capri. From what I hear, not many parts stores carry these due to it being an expensive item for them to "sit on". Please keep me informed on the status of your problem. I'd be very interested to hear whether or not you had the same issue, or if it was something else. Good luck, and I hope you get sea-worthy soon! 8)

 

[Fun Times]

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

I went to get the part, and of course nobody has one.

Get the part number you need and google the number, you most likely will find one at a good price online and ship it wherever you want/need to. Even iboats should be able to get you one pretty quickly nowadays. Good luck.

 

[alldodge]

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

Hey there 3Rivers. The tech I had look at it performed a compression test of his own on all cylinders and all were within range. He wanted to rule out the other guys incompetence, and so he did. He then decided to run the motor with the outdrive/lower end off of the motor. When he did, he heard a hell of a clanking. What he found was that the engine coupler had given out. It's possible this happened due to the engine either being misaligned, or having somehow come out of alignment. At any rate, he just found the problem today. I went to get the part, and of course nobody has one. Slim chance that my boat will be ready for the Labor Day holiday. 8( I'm sorry to hear about the issue you are having with your 3 week old '99 Capri. From what I hear, not many parts stores carry these due to it being an expensive item for them to "sit on". Please keep me informed on the status of your problem. I'd be very interested to hear whether or not you had the same issue, or if it was something else. Good luck, and I hope you get sea-worthy soon! 8)

In my novice opinion "I don't think so"[/B]. 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.