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37LX 180HP Rattle Noise High RPM WOT

jims

New member
"I have a 3.7L Mercruiser engi

"I have a 3.7L Mercruiser engine in my boat that I have put much TLC into. I just took it out for the second time this year after replacing the water pump in the drive. Temp looks good, as well as oil press. with about 180 degrees F @ WOT (4,200RPM) 35mph. HOWEVER, not long after going full throttle the engine starts making a rattling noise. Any idea what this could be? I'm hoping its not a valve problem. Maybe timing chain? The guy I bought the engine from said the cyl-head was just rebuilt.

Also noticed after a high speed run my engine runs erratically at idle, but I know that the rochester carb is in desperate need of an overhaul.

Any help on this matter much appreciated. Thanks!

-Jim"
 
what prop are you running on t

what prop are you running on that motor. not sure if it has anything to do with the rattle but I have the same engine and mine runs at 4800 WOT...
 
It could be a loose magnet rat

It could be a loose magnet rattling in the stator on the front crank shaft damper. Does your volt meter fluctuate up and down when this occurs ?
 
"Great, thanks for the replies

"Great, thanks for the replies...

-Fuel's good I have a full tank full of fresh fuel.
-I have an alternator kit installed from Hunn Finn Co. off Ebay..works great, so I tore out the old crap, except for the magnets and stator are still intact, just capped off.
- As far as propping goes, I think it's possible that may have something to do with my problem. Right now I'm running a 21 pitch prop, if it is overloading the engine it's possible that could be the source of the rattling noise I'm experiencing.
- I'll also check out the timing, Last year I set it to the specs in the manual, but I may try playing with it a bit.

I'll try the prop thing out first since it's easiest, and get back.

Thanks everybody!
"
 
but I run the same pitch... I

but I run the same pitch... I run a 14.5 by 21 pitch with a cup...how big is your boat it looks alot like mine but can't tell from avatar. mine is an open bow 19.6 feet with an alpha 1 outdrive and it runns fine..
 
"My boat's a 1987 Thompson

"My boat's a 1987 Thompson Carrera 196 Cuddy. The boat's Net weight according to NADA is 2450lbs. With it loaded up a bit its probably closer to 3,000. The boat is 20ft in length with a 7'4" beam.

I believe I have the same 14.5 diameter as you John, I'm running the quicksilver aluminum Black Diamond series. Just curious what do you run flat out? Thanks!

P.S. I can't wait to get the carb right on this thing, I believe once I get a new or rebuilt one that's been bench tested it will really preform well."
 
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