periodic knock in OMC

[cbcsr]

Let me start by saying thanks to all of you who give so much help to us new boaters. Your patience and kindness are truly appreciated. This is my first post but I have been following this board for about 4 months. I bought my first boat(1989 Bayliner 1950 Capri 3.0 L I/O OMC) about a month after I started reading this board. I bought the boat anyway.LOL I promise to listen more closely from now on. I do like the boat but it has developed a periodic knock or clunk that seems to be coming from the lower unit at 20 to 40 second intervals depending upon RPMs(2000 to 4400). Thanks in advance for any light you can shed on this problem.

 

[wau1252992]

Re: periodic knock in OMC

Hi CBCSR,<br /> My bet is that you need to check the U-joints for slack or play. You must remove the lower unit to do this, but it is not a tough job, although I have never worked on a OMC. I guess I had better let the OMC gurus advise you.<br /> Bood Boating to you! Bill

 

[clanton]

Re: periodic knock in OMC

Check gear oil for metal, shift cable from engine to outdrive must be red. Red is updated shift cable.

 

[cbcsr]

Re: periodic knock in OMC

Bill,<br />Thanks for the help. I decided to start with<br />clanton's less invasive methods first. I am not real mechanical but given enough advice I might be able to remove the lower unit.<br />Clanton, <br />I checked the gear oil, did not find any metal filings. It did seem rather dark like it may not have been changed in a while. Also checked the level and it was fine.<br />I do have the red shift cable from the motor to the outdrive. What should I check next?<br />Thanks for the quick response. I love all the activity on this board.<br />cbcsr

 

[cbcsr]

Re: periodic knock in OMC

Clanton,<br />Glad to see you back on board. Hope you were fishing and had good luck. <br />I may have misspoken when I said lower unit.<br />the clunk seems to be coming from the outdrive. Anymore suggestions? Thanks in advance.<br />cbcsr

 

[clanton]

Re: periodic knock in OMC

Lower the outdrive, remove 4 screws on top of drive remove top plate, then you can see the top gear set, check gear teeth. Plate has o-ring, so gears ok just reinstall plate, plate also has dip stick to check gear oil.

 

[Beernutz]

Re: periodic knock in OMC

Does the intensity of the knocking change when you turn the steering thru it's range or adjust the trim? If so, I'm going with the u-joints.

 

[Beernutz]

Re: periodic knock in OMC

Oh, yeah, shot motor mounts can make 'em knock, too. Just a thought.

 

[cbcsr]

Re: periodic knock in OMC

Clanton,<br />I took the top plate off and sure enough, found the top gear set. I drained enough gear oil off to see the whole set. At first I wasn't sure what I was looking for so I looked pretty close and did not see anything that looked odd. The teeth seemed sharp(not rounded off) with no play at all between them. <br />I did notice that when I put it in gear(motor off) the propellar will rotate 1/6 of a revolution. Is this normal? As long as I'm at it, 1 more dumb question. Why is the fill<br />hole lower than the dip stick, and is it ok to fill from the top as long as you get the correct level in the gear case? Two questions for the price of one. <br />If I get home from work in time tommorrow nite I'll check the frequency while turning and trimming.<br />Could I be doing more damage to something if I run it like this? Thanks for your patience and help!<br />cbcsr

 

[clanton]

Re: periodic knock in OMC

Fill from bottom to expel air. The prop has to move to align the clutch dog. Check oil level after running engine for a while with dip stick. Gimble bearing and u-joints get louder when steering turning to lock both sides, like Beernutz said.