weird engine noise

[jr438234606]

The sound is not sustained. It only makes the sound when the engine is thrown into a heavy sudden load. For example, when coasting forward, and then suddenly throwing the engine into reverse at cruising RPMs. In this case, once the boat slows, and gradually starts moving backwards, the sound stops.

The way I discovered this was when I use reverse to slow the boat--like when coming into dock. I went and checked things out on my lunch break. it appears that I may have a little too much gear oil in the gear box. I'm going to verify this, but I wouldn't think this would cause the sound.

[timebandit]

First thing I would check is to be sure the mount bolts are still tight.

[SEMIJim]

Originally Posted by jr438234606

Here are some thoughts i had:

...

Shaft is bent slightly, and only gives a problem under heavy load.

A bent shaft would cause problems, particularly vibration, at all speeds and under all loads. You can check run-out with a dial indicator, but it's very tricky to do, because any attempt to grab and turn the shaft will tend to deflect it.

Shaft alignment is another story. It could be that. Was shaft alignment checked after the boat was splashed, following the re-powering?

Originally Posted by jr438234606

Prop is cavitating.

Prop cavitation doesn't sound like a "scaping" sound, to my ear. I don't know quite how to describe it. Besides: A cavitating prop usually results in a sudden increase in engine RPMs, as if part or all the load had suddenly been removed. Also: You don't experience the thrust you're attempting to apply.

Jim

[jr438234606]

Originally Posted by timebandit

First thing I would check is to be sure the mount bolts are still tight.

Mount bolts are all still very tight. No appreciable vibration coming from engine or shaft when in gear at different RPMs. Still seems to be aligned.

I did notice a little gear box oil getting past the seal on the dip stick and dripping down the side when at high RPMs. This is why I think there may be too much oil in the gear box.

[craigtoo]

Is there anyway to verify that the prop is properly seated and mounted to the shaft? Perhaps under loads a misalignment results in uneven loading of the shaft? (maybe you've already done this...)

Barring that, I come back to the tranny because problems they are something you can hear from the cockpit. Gear Oil Sample?

[chucklesR]

I'd go with cutlass bearing. Your repower put in a more powerful engine with more torque, from the prop / keel picture the rest is original to the old system.

Simplest solution usually works, check what changed and of those things that changed which can cause the symptoms.
If it made noise in neutral it would be the motor/belts etc..if it was the tranny the tranny would be making the noise, shredding and being obvious (screwed by now and unable to shift perhaps). Simple way to check is to take a sample with the dip stick, wipe it on a clean white cloth and look hard for metal bits.

Torque shifting friction to one side of the cutlass bearing; maybe.