Engine transmission makes noise after about 1 hour of running

[Nicholasmiller]

I have had a recurring problem with our engine that I am unable to diagnose - so I am looking for help from the Afourian community!
After about one hour of running - although sometimes as long as seven hours, our engine starts to make a few minor grinding sounds, which then turn into a low pitched shriek. I have attached a sound file for your listening pleasure.
https://soundcloud.com/nicholas-mill...4-engine-noiseThe sound can be eliminated by varying the RPM up and down and occurs both in forward and if you shift into reverse after the sound has started. The sound goes away as soon as you shift into neutral. I originally thought this was clutch slip, but I am reasonably sure that this is not the case. The problem occurs at all RPMs - I normally run around 1,800, but have been running at 1,500 on this cruise. (I am posting this question in the middle of Georgia Straight in BC thanks to the miracles of LTE and WiFi.
Any help in diagnosing the problem - or even better, recommending a fix would be greatly appreciated.
Cheers,

Nick Miller

[JOHN COOKSON]

What is the drip rate on the stuffing box?
Put a finger on the pack nut. It should be near the temperature of the surrounding water. Careful around moving machinery. Do you know what type of packing you have? Dripless or whatever?
Try loosening or tightening the packing nut a bit and perhaps the sound will go away.

TRUE GRIT

[Nicholasmiller]

No stuffing box

Hi John,
I do not have a stuffing box, I use a PSS dripless shaft seal.
Thx,
Nick

[sastanley]

Nick, My boat had an alignment problem and the prop shaft wore a hole in the shaft log underneath the stuffing box hose. It was not visually detected until I pulled the stuffing box itself. It made a nice singing noise at lower RPMs, ~1,100 in my case. I am going to guess the shaft was constantly rubbing, but only that certain RPM produced the audible tone...it was exactly like rubbing your finger on a wine glass at the correct rate to make it sing.

Do you have feeler gauges on board that can allow you to check shaft/engine alignment?

Another trick is to obtain a mechanic's stethoscope, or even a long screwdriver and put the skinny end on whatever you think is making the noise and put your ear on the other end and move it around until you can pinpoint the location of the grinding/shriek.

[Nicholasmiller]

Thanks Shawn - I will try that.
Cheers,
Nick

[JOHN COOKSON]

I don't think it is the cause of the noise but while you are at it check the engine mounts to be sure they are snug.

TRUE GRIT

[ndutton]

When was the last time you burped the PSS bellows or does yours have the vent feature?

[Nicholasmiller]

PSS is burped. I am wondering if the thrust bearing is going.

[Nicholasmiller]

In my sound file you can hear the clattering that is a precursor starting at about 4 secs and the screech starts at about the 10 second mark. Then I reduce the power and throttle back up and the screech goes away. Later in the afternoon the engine ran for over 2 hours with no problems. The screech sounds really bad! Weird!
Nick

[ndutton]

As a test to indicate or eliminate the seal as the problem, next time compress the bellows - like burping except for a different reason - while it's squealing and see if it has an effect. You'll need a helmsman for this exercise and as cautioned by others, take care around moving parts. No long sleeves or jewelry.

[Mo]

Sounds drive line to me. It there any vibration in the helm when this happens? Engine movement on mounts was mentioned, I'd check that. Sure doesn't sound like the engine to me though at this point.

Listen closely to your sound video. 4 seconds in you hear a thump...then a short time later the noise, indicated by the graph. It is very possible you are picking up a piece of seaweed or something on the prop shaft and it throws it out of balance until it comes off again. The groan could be from the cutlass, stuffing box, or a combination of both...and goes away after the addition weight of the seaweed is thrown off.

That thump I mentioned...every time I pick up seaweed I hear it and I look off the back of the boat...most times you can see the culprit in the prop wash as it's ripped apart. Sometimes you can hit reverse, spinning the shaft the other way and it will come off if wrapped.

[sastanley]

Good thinking, Mo.

After a long day of motoring a couple weekends ago, and listening to the motor as not quite sounding 'normal', I had the opportunity to jump over the side and wipe the bottom down and clean the prop (no more sea nettles 'round these parts!) I figured the performance degradation was barnacles on the prop, which had a few, but it turns out I had quite a bit of weed wrapped around the prop/shaft/strut. The removal of all this plus the barnacles and she was a happy girl again.

No clunking in my case, but the all day accumulation slowly (& noticeably) degraded performance, and increased operating temps a few degrees too.

[Mo]

Yeah, just to motor 2 miles across the harbor I occasionally hit one of those strand seaweed things....the ones that are sort of like a soft tree branch with kelp or whatnot on the tip. I get the thump and look....I used to look to see if I hit a stick or something but usually seaweed off the back. Occassionaly I'll loose rpm if it's big enough then she'll either throw it or I hit reverse with the boat still with forward momentum and it will roll off the shaft and be visable off the stern. FWIW

[Nicholasmiller]

After the clattering starts (around 4 secs on my sound file), I can usually prevent or delay the onset of the screech by modulating the throttle. It is definitely not seaweed, although when it first started happening a few years ago I initially thought that this might be the case. I am sure that the problem is mechanical. The engine mounts are good and there is no vibration on the helm when the problem happens. I have readjusted the forward and reverse according to the instructions to get a good neutral as my neutral was hard to find, as I wondered if heat could be causing expansion and causing the transmission to try to be in forward and reverse at the same time. I have also checked the prop shaft for play and there is none.

Initially, I thought the noise was clutch slip, but I am fairly sure that it is not (I use 10/40 Castrol motorcycle oil).
If it was a bearing, I would have thought the problem would be evident right away rather than the engine operating OK for up to 7 hours (but usually 1 or 2 before the problem starts). Perhaps we can get the Maestro, Don to chime in with his thoughts.

If I have to pull the engine I am thinking of getting a new or refurbished short block from Don as the engine is over 40 years old and until 2 years ago has been sea water cooled. Other than the problem I have described she runs like a swiss watch, although I think I need a new manifold as I am losing coolant.

Puzzling?!?!

Thanks everyone for all your ideas and suggestions!
Cheers,

Nick

[BunnyPlanet169]

I have also checked the prop shaft for play and there is none in the vertical axis but there is some in the horizontal axis - anyone know if this is normal?

This is not normal, and would support the worn cutlass bearing theory.