Mercruiser 3.7L Engine Noise

[altcoak]

I have twin 3.7 Mercs On starting the port engine there is a noise that sounds like a "moan".<br />The "moan" goes away after the engine warms up. The problem doesn't show up on starting the starboard engine. Oil pressure and water temp are in the correct operating ranges on both engines. The Merc mechanic at the marina has no idea of what the problem is. Any thoughts?

 

[Walt T]

Re: Mercruiser 3.7L Engine Noise

Can you isolate it? front? rear? side? Disconnect the alternator belt, then any other belts, see if that makes it go away. Could be a gimbal.

 

[altcoak]

Re: Mercruiser 3.7L Engine Noise

All belts are off. As best I can tell the noise is coming from the front of the engine. Additional info, the engines are 1989, 165 HP,<br />3.7L.

 

[Walt T]

Re: Mercruiser 3.7L Engine Noise

Does this still have the alternator mounted to the crank up front?

 

[altcoak]

Re: Mercruiser 3.7L Engine Noise

Yes, the alternator is mounted around the crank.

 

[flashback]

Re: Mercruiser 3.7L Engine Noise

Well if all the belts are off and your still getting the noise it must be in the engine, although sounds sometimes telegraph from one area to another and can mislead you. good luck......one place it could be is a worn timeing chain and gears if the sound is truly in the front of the engine.......

 

[chiefmike58]

Re: Mercruiser 3.7L Engine Noise

altcoak, I also have twin 3.7s and get a moaning noise such as you described. I changed starter, gimbal bearing, pulled front pulley to check out stator, etc., and found nothing. Warms up and there's no noise and doesn't do it all the time either. Anyway I've noticed it for 3 seasons now and all is well. I'm thinking that it might be the alternator creating drag when first starting charging battery, although I have no evidence of this. Mike

 

[Trevor]

Re: Mercruiser 3.7L Engine Noise

hey I have twin 3.7lxs I am repowering the one engine that has probubly the same moan as you descride chech your compression I had one low and was told that this was the problem. also the alighment was out on the gimbal bearing but the main problem was the compression. the motor made the noise with the drive off as well. I have a posting here about the motors. Good luck Trev.

 

[altcoak]

Re: Mercruiser 3.7L Engine Noise

Thanx for the tip, will check the compression.<br />have a Merry Christmas.

 

[altcoak]

Re: Mercruiser 3.7L Engine Noise

Sorry I didn't back to you sooner. Every time I tried to log on I received a "site not available msg". Will look into the alternator for problems.

 

[Peter3708]

Re: Mercruiser 3.7L Engine Noise

I have a 3.7L and have the same condition. After things get warm the moan goes away. I really think that the noise is either the gimble bearing or the shaft/gimble alignment. I am religious about greasing the gimble bearing.

 

[Blue Thunder]

Re: Mercruiser 3.7L Engine Noise

To see if it is the gimbal bearing, start the engine, and while the moan is happening, pump grease into the bearing. If the noise changes you know its the bearing. If not, keep searching.<br /><br />BT