What's a healthy engine sound like?

[pbyrne]

I've been reading with interest the thread on alternator belts and engine temp, and taking a look at my engine.  At 23 years old, but low hours (less than 900), it seems like it's in good shape, but I don't know what a diesel marine engine is supposed to sound like.  I have no reference, as compared to a car, which I know what is normal.

This may sound odd, but can I get some feedback on the way the engine 'sounds'?  There are 2 vids, one idiling and another with forward engaged at idle.  She's tied up at the dock still if that matters.

How does the old girl sound? Anything to look into?  Also, a couple of pics of the back of the engine, just in case!

Idle:
https://www.youtube.com/shorts/bQR5bexjS8Y

Idle Forward:
https://www.youtube.com/shorts/xhTce5ix298

[Ron Hill]

pby : Sounds like a normal diesel to me!!  Is there any vibration?

and when was the last time you checked the valve clearance??

A few thoughts

[pbyrne]

pby : Sounds like a normal diesel to me!!  Is there any vibration?

and when was the last time you checked the valve clearance??

A few thoughts

Well there's what I'd say is normal vibration from a running engine. The engine moves a bit on the mounts, meaning it's not rock solid, it shimmy's at idle more than a car engine if that helps.

The only thing I would say is that when I shift into reverse to decelerate, after pausing in neutral, there's a shrudder and then it settles down. There is a variprop 3 blade on her, so I assumed the shrudder is normal as the blades move into reverse pitch, but....?

Also, you can see in the video with the transmission engaged that the stuffing box and shaft move ever so slightly.  Not a vibration, more a swaying motion.  No idea if that's an issue...

I also seem to find a couple of cups of antifreeze in the bilge, and the overflow bottle is empty in the spring after the winter.  Engine is full of coolant, and I just top it up and it doesn't happen during summer months.  Can't figure this one out.  I've tightened all the hose clamps I can see.

No I don't think the valves have ever been checked for clearance. I know I haven't done it in 3 years.

Sorry, there's a number of points here!

[mregan]

Sounds just like mine, but a lot less rust.

[Ron Hill]

pby : I don't think you have a problem!!

A gasoline auto engine always will idle much smoother than a diesel.
i would say your shaft movement is normal.
On your coolant leak - have you placed a fuel diaper under the engine?  Annual Loss of all of the fluid in the coolant recovery bottle is NOT normal. You have a leak!
I always adjusted the valves myself (with a helper) every 1000 hrs. 

A few thoughts

[Kyle Ewing]

pby--I'll add video of mine running soon for additional reference.  Here's a video of the first start of the season to show ease of starting of a 30+ year engine.  https://youtu.be/eWyPu0EdxJA

[pbyrne]

pby : I don't think you have a problem!!

A gasoline auto engine always will idle much smoother than a diesel.
i would say your shaft movement is normal.
On your coolant leak - have you placed a fuel diaper under the engine?  Annual Loss of all of the fluid in the coolant recovery bottle is NOT normal. You have a leak!
I always adjusted the valves myself (with a helper) every 1000 hrs. 

A few thoughts

I agree.  I'm just not sure where the leak is.  I did notice a 1" diameter pool of coolant below the connection to the heat exchanger on the port side of the engine at the rear.  I'll have to get a photo.  I was installing an AIS system and noticed it with the boards in the aft cabin up.  Bascially if your looking at the rear of the engine approx. the point where the heat exchanger connection is, directly below it.

[pbyrne]

pby--I'll add video of mine running soon for additional reference.  Here's a video of the first start of the season to show ease of starting of a 30+ year engine.  https://youtu.be/eWyPu0EdxJA

Nice!  Is it a Westerbeke?  Mine does the same thing, just fires right up after sitting all winter.  Not more than a few cranks and away she goes.

[Breakin Away]

One thing that I noticed is that your belt is a little loose for my taste. I see some wobbling on the left and right sides. I don't like that and I try to have enough tension that it's taut all the way around when running. In my experience, that wobbling can be enough to create a little vibration. That's just me, it's possible that I over-tighten mine, but I like it that way. Replacement belts are $5, so they're cheap to replace if they wear faster.

Also, you can see in the video with the transmission engaged that the stuffing box and shaft move ever so slightly.  Not a vibration, more a swaying motion.  No idea if that's an issue...

That swaying could be a sign of a few different problems. You shaft could be slightly bent or wobbling (especially since it's bronze), your coupler might need re-facing to ensure it's perpendicular, and/or your engine could be out of alignment. The easiest thing to do first is to manually rotate the shaft by turning the coupler. When doing so, is the resistance uniform throughout all 360 degrees of rotation? If so, that's generally a good sign. Another option is to detach your coupler and verify its alignment with a feeler gauge (and also check its alignment through all 360 degrees of rotation). This is something that you should do with the boat in the water, since the boat can flex on the hard.

I notice you have that white insert between the transmission and coupler flange. I have no personal experience with those, so don't know if they're meant to flex and make perfect alignment less critical. But I know from my polymer science background that anything that's elastomeric also has resonant frequencies that might cause bad things to happen at certain RPMs, so they're not always an improvement.

More importantly, if that white insert was added without shortening the shaft to compensate, your prop has been pushed back another inch or two from the strut/cutlass bearing. I believe that the guideline is to have no more than one shaft diameter of distance (1" in your case) between the front of the prop and the back of the strut, otherwise you may be susceptible to shaft wobble (especially with a bronze shaft). I think Maine Sail has written a lot about these issues, so go search around https://marinehowto.com .

I don't mean to make you nervous, everything is probably OK, but if you wanted some ideas I'm offering them. Feel free to ignore them if you prefer.

[pbyrne]

One thing that I noticed is that your belt is a little loose for my taste. I see some wobbling on the left and right sides. I don't like that and I try to have enough tension that it's taut all the way around when running. In my experience, that wobbling can be enough to create a little vibration. That's just me, it's possible that I over-tighten mine, but I like it that way. Replacement belts are $5, so they're cheap to replace if they wear faster.

Also, you can see in the video with the transmission engaged that the stuffing box and shaft move ever so slightly.  Not a vibration, more a swaying motion.  No idea if that's an issue...

That swaying could be a sign of a few different problems. You shaft could be slightly bent or wobbling (especially since it's bronze), your coupler might need re-facing to ensure it's perpendicular, and/or your engine could be out of alignment. The easiest thing to do first is to manually rotate the shaft by turning the coupler. When doing so, is the resistance uniform throughout all 360 degrees of rotation? If so, that's generally a good sign. Another option is to detach your coupler and verify its alignment with a feeler gauge (and also check its alignment through all 360 degrees of rotation). This is something that you should do with the boat in the water, since the boat can flex on the hard.

I notice you have that white insert between the transmission and coupler flange. I have no personal experience with those, so don't know if they're meant to flex and make perfect alignment less critical. But I know from my polymer science background that anything that's elastomeric also has resonant frequencies that might cause bad things to happen at certain RPMs, so they're not always an improvement.

More importantly, if that white insert was added without shortening the shaft to compensate, your prop has been pushed back another inch or two from the strut/cutlass bearing. I believe that the guideline is to have no more than one shaft diameter of distance (1" in your case) between the front of the prop and the back of the strut, otherwise you may be susceptible to shaft wobble (especially with a bronze shaft). I think Maine Sail has written a lot about these issues, so go search around https://marinehowto.com .

I don't mean to make you nervous, everything is probably OK, but if you wanted some ideas I'm offering them. Feel free to ignore them if you prefer.

Yeah, it's one of these.  https://www.pyiinc.com/flexible-shaft-couplings.html 

I will check the gap as you mentioned, and I think the PYI also has a spec for the same thing.  I was wondering about the space between P bracket and prop.  When I read about that the first time, the gap looked suspiciously the same as the coupler...  I check the cutlass bearing every year and there is no play.  But... the engine has low hours on it.

[Noah]

Your shaft may be a bit too long, as the prop could/should go closer to the strut. This is just a guess and I may be all wet! It may be a none-issue. 

[Breakin Away]

I agree with Noah, the gap between the prop and strut is a little larger than ideal, but may be a non-issue.

I will check the gap as you mentioned, and I think the PYI also has a spec for the same thing.  I was wondering about the space between P bracket and prop.  When I read about that the first time, the gap looked suspiciously the same as the coupler...  I check the cutlass bearing every year and there is no play.  But... the engine has low hours on it.

To clarify, the type of "wobble" I'm talking about could occur even with a well-aligned and unworn cutlass bearing. You will not detect it by manually moving the shaft - only under dynamic load while in gear. Our boats have the shaft constrained at only two points near the ends - at the strut and the packing gland - with a pretty long shaft run between them. That length can lead the shaft to dynamically flex at certain RPMs due to dynamic torsional loads, kind of like a guitar string vibrates between two frets. This problem is made worse when there is too much shaft between the strut and the prop. In such cases, the slightest balancing issue with your prop, or even a hydrodynamic interaction between your prop blades and the strut or little keel-skeg over the prop, can provide the vibrational driving force that causes dynamic shaft whip between the constrained ends of the shaft.

Maine Sail had written about this on a website somewhere, but I can't find it. I specifically remember him mentioning that Catalina's drive train design  was particularly susceptible to this (due to the long shaft length between the two constraints), and mentioning that bronze shafts were more susceptible than SS alloys like Aquamet (since bronze is softer).

This may be a total non-issue for you, so don't get overly concerned. Just keep it in mind if the problem gets worse.

[Breakin Away]

Regarding shaft whip, I just found this thread where Maine Sail posts a number of useful comments. The link goes to one of his comments, but you should read the entire thread if you have time. It describes what I was trying to say:

https://forums.sailboatowners.com/threads/prop-shaft-runout.103188/#post-581542:~:text=It%20is%20also%20important%20that%20the%20exposed%20space%20between%20the%20prop%20and%20strut%20does%20not%20exceed%20the%20diameter%20of%20the%20shaft%20it%27s%20self..

[Noah]

The fear of prop whip was one reason I replaced my original bronze shaft with an Aquamet 22 SS shaft, when I traded-up to my heavy 3-blade Flexofold folding prop. No issues after 6 years of use.

[Breakin Away]

Aquamet 22 + Flexofold 3-blade here too for the past 4 years. I love the combination, and the FF prop has allowed me to sail in light wind conditions when I used to have to motor. (Chesapeake summers) I've passed a lot of boats up to 45' in light air. I can often sail on genoa alone at 6-6.5 kts if the wind is 7 kts or higher. My hydrodynamic drag is dramatically reduced.