3.7 engine noise @ rev-up only.

[heebe]

I have a Mercruiser 3.7 engine. I rebuilt the top part of the engine and it ran very good for about 10 hours. Now the engine idles fine but when I acclelerate it has a rapping sound. It sounds very nice at idle but raps like hell when reving it up. Any troubleshooting tips would be appreciated. Thanks, heebe.

 

[tashasdaddy]

Re: 3.7 engine noise @ rev-up only.

check valve adjustment. and timing.

 

[heebe]

Re: 3.7 engine noise @ rev-up only.

mechanic say's valves are not adjustable only tighten down and we checked them. If the timing were out the idle would not be good like it is.

 

[Bondo]

Re: 3.7 engine noise @ rev-up only.

Originally posted by heebe:<br /> mechanic say's valves are not adjustable only tighten down and we checked them.

Well,.......<br />If it's Not the Top-end of the Motor,..........<br /><br />It's Got to be the Lower-end.........Bad Piston,.?? Bad Bearings,.?? Bad Rod,.??

 

[KaGee]

Re: 3.7 engine noise @ rev-up only.

Not to mention something may have came loose or bad push rod or lifter?<br /><br />Like Bondo said... isolate where the noise is coming from.

 

[DHPMARINE]

Re: 3.7 engine noise @ rev-up only.

When it's rapping,pull one plug wire at a time.This may at least indicate which cylinder to focus on.I don't recall what years,but some of those 224's had issues with the water resevoir to manifold gasket.I think water got into cylinder 3 or 4 and caused the wrist pin to seize ?<br /><br />DHP

 

[Mischief Managed]

Re: 3.7 engine noise @ rev-up only.

Spark plug wire tip is excellent. You may wish to take the belts off to isolate the engine from the belt driven accessories. Sometimes it's something you would not expect to make such a noise like the circulating water pump or the power steering pump.<br /><br />Could also be the U joints...

 

[Reel Poor]

Re: 3.7 engine noise @ rev-up only.

Could be fuel pump.

 

[Rod Holder]

Re: 3.7 engine noise @ rev-up only.

Hey heebe,<br />Did the rapping start all of a sudden while cruising or was it progressive ? Reason I ask is that (before rebuilding) mine had some piston slap and eventually #3 piston skirt gave way at cruising speed and really started wobbeling back and forth causing a horrible (as in poodles jumping into the arms of rather spiffy looking dockside onlookers) rapping sound. Very loud.<br /><br />If you do a search on "rapping sound" you will see my experience (which I hope will not be yours) johnkc hit the nail on the head on that one as others have also on this post.<br /><br />Definetly do as suggested by these guys and try and isolate if/which cylinder it is.<br /><br />Wish ya luck......RH

 

[dnsellers]

Re: 3.7 engine noise @ rev-up only.

I had a similar situation w/ a 3.0 merc...turned out to be a spun bearing It seemed to make little or no noticable noise @ idle, but when powered up it was an very noticable and loud rackett. I sure hope its nothing serious bud, mine required a new engine. A lot of what everyone else it discussing (not to question anyones knowledge in ANY way) would be noise heard constantly...both @ idle and giving it gas. Valves, etc.. Bearings are tricy sons of b's.