Engine or Drive Knock...

BoomerangII

BoomerangII

New Member
May 20, 2010
56
New York
Boat Info
245 Weekender
Engines
5.0 Mercruiser w/Bravo III
Here we go...

2001 5.0, Bravo III. Just summarized and started today. Engine Starts, temps good, oil pressure good, idles smooth. BUT, when engine is brought out of idle, I hear a knocking noise. Sounds like the rear of engine near transom. Somewhat worse when drive is in tow mode (up).

There is no white smoke in exhaust and oil looks good. Gimbal bearing was replaced three seasons ago and drive has never been serviced since (please be gentle) :smt021

I have probably just answered my own question and have searched a plethora of past post on U joints and various engine knocks, but, I am still wondering if this sounds like a universal joint issue or other. Will be bringing into shop for service and would like to have somewhat of a clue before I walk in there...
 
Set the drive level to kill as much universal influence as possible. Use a long screw driver and listen to.different points on the running engine. It should help pin point the knock.
 
I was considering that. ER is very tight though, will have to see what I can do tomorrow. I hate to run the engine if it is a rod or bearing, don't want to make it worse. Calling service in the am.

mwph: just shy of trailer high. I did level the drive as much as possible w/out bottoming out on the driveway and noise was still there when throttling just above idle (less than 1000 rpm) and gets louder as you increase throttle.
 
Could also be the coupler - which means the engine needs to be pulled. Get your drive serviced soon.
 
If it gets louder above idle with the engine level don't bother starting it. It's going to need
more than you can fix in the drive way. Let us know how you make out.
Good luck.
 
BoomerangII said:
I was considering that. ER is very tight though, will have to see what I can do tomorrow. I hate to run the engine if it is a rod or bearing, don't want to make it worse. Calling service in the am.

mwph: just shy of trailer high. I did level the drive as much as possible w/out bottoming out on the driveway and noise was still there when throttling just above idle (less than 1000 rpm) and gets louder as you increase throttle.
Click to expand...

You should not be running the drive in gear with the drives trimmed anywhere near trailer level. The u-joints are really angled at that trim setting and that knocking is bad news. Never run it in gear trimmed higher than it goes with the regular trim switch. If it does not knock in the normal trim range then it is probably OK.

The drive should be lubricated and serviced at least once a year.
 
The shaft is turning whether it's in gear or not. Your knock/noise gets worse as you raise the drive so I'd vote for u-joints. Does the knock change when you turn the steering wheel L or R?
 
Creekwood - Never in gear, this is when the drive is not engaged and I'm just running engine.
Mystic - Thats my thought as well. It's going to the shop...freaking bummer.

I'm more pissed at myself than anything, lack of service. I'm "hoping" its something with the drive and not engine, at this point i"m not 100% sure.

Thanks again guys, I'll keep ya posted...
 
BoomerangII said:
Creekwood - Never in gear, this is when the drive is not engaged and I'm just running engine.
Mystic - Thats my thought as well. It's going to the shop...freaking bummer.

I'm more pissed at myself than anything, lack of service. I'm "hoping" its something with the drive and not engine, at this point i"m not 100% sure.

Thanks again guys, I'll keep ya posted...
Click to expand...

The limited listed symptom does sound consistent with a failing universal joint in its early stage of failure, not the worst thing in the word.

TABMAN, just for your own reference, the universal joint is spinning anytime the engine is running, it does not matter if you have the drive in forward, neutral or reverse.

The cone clutch is inside the Bravo III drive past the universal joints.

Also, the noise is dramatically worse out of the water then in. I was not with you to hear your knock. It’s possible you have no issue.

The solution is to have the drive pulled & serviced. This includes getting various parts lubricated, gimbal torqued, parts inspected for water intrusion, rot & wear, various items inspected, alignment check, coupler check, universal joints checked, new O-rings then have it reinstalled.

Have you been changing the drive fluid each year? If not, also have them do this.

Tell them your concerns & observations. They will pay close attention to the universal joints and give you their recommendations.

I’m still hoping the answer you will get is your only issue is a lack of service.

Please let us know what you find out. I’ll keep my fingers crossed for you.
 
Last edited:
Well, just dropped off to a "new to me" mechanic. Keeping my fingers crossed...:smt089
 
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