1999 200HP Merc. OB knock

[rodbuzz]

Have a 99' 200HP Merc. outboard (not EFI). It's been well taken care of. Have a low knocking/grinding sound in the engine at idle (haven't taken it out since the sound). A few days before this I noticed an air leak in my oil tank cap and tightened it. It seemed more white smoke came out of the exhaust. But, the oil was being used because the tank was lower since i filled it and the reserve was full. No alarm went off at all. I had a mechanic come check it out. He did compression tests and they came out ok. He told me to start looking for a new powerhead. Would the compression be ok if it really were a knock or a broken rod or could it be something else (fuel/oil related??) Plugs have been changed already and he also ran the motor taking each spark plug wire off at a time. Not really sure what to do or have checked. Any suggestions would help. Thanks

 

[Kenny Bush]

Re: 1999 200HP Merc. OB knock

Rodbuzz, something doesn't sound right. If you did not get enough oil through the motor, the pistons would be the first thing failing, and a routine compression check would show this. Hmmmm, we need more data for the board to come to a solution. I have seen timing problems cause knocking sounds, but your mechanic(if he is competent) should be able to distinguish. Mercury has had problems with double firing and this usually leads to the piston melting away at the exhaust port. Maybe you have not scoured it enough to cause rings to stick and loose compression. I think you need another compression check and post the readings. Get us more information.....this does sound challenging.

 

[HowieDean]

Re: 1999 200HP Merc. OB knock

Most likely your oil pump is starting to go away... And it is what is making the noise... You most likely still have good oil flow and haven't hurt anything inside the motor... "yet" The other things it could be are either the top or bottom bearing starting to fail... I would take it to some-one good... and have them check it for you...<br />Try.. Marine Dynamics<br />511 North Britain Road - Irving, TX 75061 <br />(972) 438-8399 <br />I drag race with these guys and they are good people who really know there stuff....