Engine noise

[Speakrdude]

Hey All, Long time, no see!

Well my first LARGE project boat is finally at her new home at the dock now. Finally after almost 3 years of work (Thanks Don S. )

http://rides.webshots.com/album/110268993cbtppY?start=56

Anyway, After cruising for a while this weekend, The engine has started making a slight knocking noise at idle to 900ish RPMS.
The noise is there now regardless of engine temp. It appears to be coming from the rear or even the bell housing area.
No noise after 900~1000 rpm's and no noise at hole shot or under a load. (as far as I can hear anyway)

Oil PSI is 45 at cold idle and 55~60 at 3800 RPM's. When everything gets warm, idle psi is 10ish and anything over 1000 rpm's is 45ish.
Engine runs real nice and smooth with plenty of power. Comfortable cruising speed is 26~28 MPH @36~3800 RPMS.
The noise doesn't appear to be coming from the drive as I have tried the side to side method of the drive to hear a change.
Something that did happen right before then, while I was accelerating pretty fast once Sunday to get on plane, the boat seemed to "blow-out" or slip trying to get on plane. I immediatley brought back down to idle then accellerated more slowly, no problem since then.

Any thoughts?
Jim

 

[Speakrdude]

Re: Engine noise

Lets try this link..

http://rides.webshots.com/album/110268993cbtppY?start=56

 

[FreeBeeTony]

Re: Engine noise

All I can say is WOW........the boat looks like new!!

What does it weigh? Is that a 350 SBC?

 

[Speakrdude]

Re: Engine noise

Thanks, The boat weighs 3 tons! Yes the engine is actually a 1970 model GM 350.

 

[searay3]

Re: Engine noise

Don't know which drive/engine you have, but since you describe a blow out, engine revving and little or no motion?....pull the drive and have a look at the coupler and prop. I would start there....

 

[Speakrdude]

Re: Engine noise

Engine is GM 5.7L w/Volvo 280 completely refurbed.

 

[Don S]

Re: Engine noise

That boat has come a long way from the first picture I seen of it. Light blue hull, green growy stuff all over it, sitting on the trailer backwards! ! ! !
Are you sure the noise is the engine, and not coming from the bearings in the bellhousing? Does it sound like a lifter rattling? Might make sure the oil level isn't too high, that could cause areated oil which would allow lifters to collapse a little.
Now, on to your slippage. Are you sure the shift linkage is moving all the way to forward when the engine is running?
Pull the prop and the back cover off the drive. Start the engine and have someone shift to fwd. Then see if you can turn the mechanism any further by hand. It's possible it could slip under a real heavy load, but not under normal starts. Water in the gear lube could cause that also.

 

[Speakrdude]

Re: Engine noise

Thanks Don, I will research all of your suggestions.

Jim

 

[Speakrdude]

Re: Engine noise

Well, I did some research and the noise seems to be coming from the transom shield area, not the engine.

You cannot hear it coming from the drive on the outside, only from the drive area on the inside of the bilge.

Maybe I damaged a U-Joint or shaft bearing some how when I "blew-out" that time. All the bearings, U-joints and related are new with only 44 hours total on them now.

 

[Don S]

Re: Engine noise

If you can't hear it from the drive side, my guess would be either the intermediate bearings in the bellhousing or the flex plate that attaches to the flywheel.
If the springs in that flex plate fail, they can cause some knocking noise.
Your only choice is to pull the upper gear box and check the ujoints. If they are ok, then it's an engine pull to check the intermediate bearings and flex plate.