Rattling diesel, again.

[Gaia]

We have a mystery rattle in our 3YM30 Yanmar that has slowly worsened during a four month visit of the Bahamas. I want to stress that this is a new noise. One we have not heard before. We are quite aware that diesel engines are noisy beasts. During this visit to the Bahamas we motored about 35 hrs and then added another 24 on the passage from West Palm Beach to Port LaBelle using the ICW and the Okeechobee waterway. We were only able to sail about six hours on this homeward bound passage.

The rattle occurs on startup only, after sitting for 20 hrs or more and lasts about four minutes now. It is now quite loud and can be heard on top. It tapers off after two minutes and over the next two minutes seems to cycle with a period of about a second. A second or so louder and then a second or a little less more softly, another increase until disappearing after about another two minutes. The motor is at idle.

In a 2012 post on this forum with similar symptoms but an only 4 sec duration the cause was found to be in the alternator. Our 'noise duration' is much longer. One suggestion on that post was big end bearings which of course worries me. And I can imagine that disappearing in a short time after start up as oil reaches the bearing. What I do not understand is why big end? Why not other bearings? And how does one know? Someone else suggested fresh water pump bearings but I would think that the sound would not disappear in that case. I have used a stethoscope particularly around the valve cover but have not been able to trace the source. My next step will be to check the tappet clearances but in the meantime I wonder if anyone else has experience with this slowly disappearing clattering sound. I should add when I start the engine immediately after shutting it down there is no sound. If I start it say four hours after shutting down, which i just did to check, there is little and perhaps no sound. The next day however the sound returns.The oil pressure seems normal running around 40 psi at 1600 rpm when hot and maybe 20 or 25 idling. Engine starts well, on the first stroke, runs at normal temps and could even be described as 'purring' (-:. There is no smoke but after a longer run especially at somewhat higher revs of way 1800 rpm (we baby the engine, some say excessively) there is slight 'sooting' of the hull.

If the valve clearances check out, as I assume they will since I last checked and adjusted them in January, my next step I fear will be to overhaul the engine, something I would rather not have to do 🤔. Unless someone else can suggest another course or action. ?

The engine used no oil in the Bahamas but used a little on the homeward run when I drove it a little harder. It is about ten years old but has only about 1500 hrs mostly from anchoring or arriving and departing during a slow circumnavigation. I should add that the engine comes up to temperature normally during anchoring and departing as we are conservative sailors. It was bought in New Zealand.

An expert opinion would be much appreciated.

Jim

[a64pilot]

Big end bearings almost always are a hollow knock, and they don’t do it until the motor is hot, it’s not a rattle at all. It’s a slow, steady hollow knock, it’s not a rattling knock at all, like I think you have. Your sound is more of a clatter than a knock right?

I’m going to bet lunch that you have dirty injectors, it’s very common, the fine spray isn’t a fine spray anymore and that changes the timing of ignition, and makes it knock like a cold Diesel.

Your injectors need cleaning, what used to be done many years ago was add automatic transmission fluid to the fuel, it’s high detergent oil and can help clean varnished injectors somewhat.
Try to get some seafoam or auto transmission fluid, don’t get synthetic auto tranny fluid, I’m not sure how well that would work.

There are NAPA stores in the Bahamas, Rock Sound I know has a good one.

When you get home pull the injectors and have them cleaned, you should every 500 or so hours anyway.

I’m betting that there is nothing wrong with your motor.
If your worried about bearings, don’t waste your money and time on an oil analysis as people will tell you to do, but do pull your oil filter and inspect the media, there are videos that will show you how to.
If you have a spun bearing, which I don’t think you do at all, with that oil pressure, there will be considerable metal in the oil filter.

[Gaia]

Many thanks for that encouraging comment. I will pull them and have them cleaned.

A very knowledgeable friend keeps saying that he suspects the lifters and I will check the valve clearances at the same time.

I am keeping my fingers crossed as I am willing to tackle rings etc but not crankshaft removal in my cockpit (-:

TX again

Jim

[a64pilot]

Dirty injectors do sound very similar to what is often called valve rattle.
Remember the cars of the 70’s how they would rattle pulling a hill?
Well it’s called valve rattle, but it has nothing at all to do with the valve train.
It was actually pre-ignition, which is similar to what I believe you have.
It was not detonation as that is different and extremely damaging.

However a few autos will suffer from what amounts to sludge building up and blocking off the flow of oil to hydraulic lifters, and they will tick when cold, the 90 to 97 Mazda Miata’s were famous for this, but that is a light tick, tick, which isn’t want you have if I’m correct.

This is a really bad example of a hydraulic lifter “tick” on a Miata
https://youtu.be/MD9Qu19SWt0

Oh, and by all means THE time to adjust valves is when the injectors are out, cause there is no compression and the engine is easy to turn over.

[Gaia]

And a ps a64pilot: yes, it is very much more clatter like than a knock.Quite a high frequency, tinny 8 would say. Interesting how hard it is to describe a sound. More a rattle than a knock as well although I must admit I have not heard an engine knock since my youth, 60 yrs ago (-:

Jim

[a64pilot]

By the way, I’m pretty sure we don’t have hydraulic lifters, and are pretty much immune to lifter tick unless they are adjusted way too loose, which about the only way that is happening is if you forgot to lock down the jam nut last time you adjusted them.

Hydraulic lifters self adjust and should never need adjusting, vast majority of older US cars are hydraulic, and that is why nobody adjusts the valves on their Buick.

We have to adjust ours, which is why I believe they are solid lifters.

[Gaia]

Yes, this engine has solid lifters. I was reminded that if clearances are required the lifters are solid.

Will do the check tomorrow and get back on this thread

Jim