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If the engine ran OK after you put the new injectors in them & the knock just suddenly appeared afterwards, it is possible something fouled an injector tip, effecting the spray pattern? The fact that the knock just "went away" may indicate a temporary problem with the fuel delivery system?

As Rich mentioned timing is critical and should be checked. You might want to pull the injectors and have them checked by a shop. I have read that water reaching the injector tips can cause damage to them. Perhaps check your water separator for any water accumulation?

I have heard diesels that knock somewhat when cold but as they warm up the knock subsides, but that is different than your description. Let us know what you find.

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Two kinds of knock, ignition & bearing. Ignition, kind of like a ping in a gas engine, short & sharp. Bearing, kind of low frequency, longer duration, awful sound. I think if it was a bearing it would be constant & not "go away"? Suggest you try the easiest things first. I don't know the specs for that engine, but 10 lbs at operating speed seems a bit on the low side?

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Got the manual, and know how to adjust the valves, but the timing marks are IMPOSSIBLE to check while the engine is in situ, unless I use an inspection camera... and I don't have one.:(

This also would not fit with the fact that it seems to have, at least temporarily, fixed itself...:confused:

Naw, the M25 rev range is from 1000 to 3200RPM. (my idle is around 800RPM).

But the point is valid, that I was pushing the motor shortly before this symptom manifested itself.

This is a diesel, so I think that I can rule out ignition problems.;) I agree that a bearing would not fix itself.

I think that the end of the season may be time to finally pull the motor (not a job that I look forward to). I also have a PSS shaft seal, which means that the boat will have to be hauled.

Yes the decreasing oil pressure has been a long running mystery. It starts out at 50 PSI, the gradually drops, but never so low as to sound the alarm. It has done this for the past 2 years, possibly longer.

My suspicion is that I may have an exhaust valve which either stuck open, or was opening prematurely (dirt?)...
I should have said "combustion", instead of "ignition".

Paul T
 

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As it "comes & goes" it may be a valve that is not closing all the way or debris/water lodging in an injector. Not much you can do if it is a valve except to take off the head & have a shop "service" it or replace bent/scored valves. Maybe after it is thoroughly heated up a bent/scored valve may hang up. A stretch, but maybe a bad or broken valve spring?

Injectors may also be effected by heat? Easier to have them checked by a shop, although until they are hot they may test OK?

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Thanks Paul,

I took her out today, although with the 10-15kt winds, I didn't need to motor very much. However, the engine sounded fine every time that I used it during the journey.

I think (and hope) that it was the valve adjustment.

I will keep you posted.
Well, that would be good. I wonder why one valve could be so far out of spec?
Has there been any work done before the problem surfaced?

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I installed new injectors last winter, replaced the valve cover gasket (not needed), and upgraded the heat exchanger from the 2" to the 3"... nothing that should have mussed up the timing though.
The more I think about the intermittent nature of the problem the more I think it may be an injector problem. When knocking and putting out excess smoke one of the injectors may not be producing a proper spray pattern, due to debris or water?

If it was fuel starvation I think you would just lose power. Kind of sounds like fuel may be puddling up? Are there any indications that excessive blow by vapors can be collecting in or near the intake tract?

Having the injectors checked by a shop would be easier than pulling the head?

James' comment about cetane additives would be an easy try. Or maybe a heavy duty "cleaner" additive? I used to use this in my VW diesels & never had any fuel related problems:

DIESEL KLEEN庐 +Cetane Boost庐: Max HP Formula ? use during non-winter months for the ultimate in performance.

I am sure there are lots of different additives that may be as good or better?

Paul T.

Edit: Just saw your picture, the tanlk has been around for a while.:D

I did some tests with the Power Service additive a long time ago. Put some diesel in a coffee can, added a little water to it, then added the additive & the water was no longer visible. A tank that old may very well have some water in it. However, a good filter/separator should catch it. Some units have a clear bowl on the unit allowing you to see water or debris.

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The more I think about the intermittent nature of the problem the more I think it may be an injector problem. When knocking and putting out excess smoke one of the injectors may not be producing a proper spray pattern, due to debris or water?

If it was fuel starvation I think you would just lose power. Kind of sounds like fuel may be puddling up? Are there any indications that excessive blow by vapors can be collecting in or near the intake tract?

Having the injectors checked by a shop would be easier than pulling the head?

James' comment about cetane additives would be an easy try. Or maybe a heavy duty "cleaner" additive? I used to use this in my VW diesels & never had any fuel related problems:

DIESEL KLEEN庐 +Cetane Boost庐: Max HP Formula ? use during non-winter months for the ultimate in performance.

I am sure there are lots of different additives that may be as good or better?

Paul T.

Edit: Just saw your picture, the tanlk has been around for a while.:D

I did some tests with the Power Service additive a long time ago. Put some diesel in a coffee can, added a little water to it, then added the additive & the water was no longer visible. A tank that old may very well have some water in it. However, a good filter/separator should catch it. Some units have a clear bowl on the unit allowing you to see water or debris.

Paul T
Thought maybe you might have missed the edit.

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Molecules of water going thru the injector tip tear helll out of the tiny holes Bad spray pattern can blow holes in the piston top. Sounds like knocking until the serious blowby starts. Some fuel additives can carry the water to places it's not meant to be .Catch it early.
I have read about but never had the water/injector problem, that I know of. If there is water in the tank It would be good to get it out before it goes into/thru your filter/separator. From the picture it looks like there is a port cover/cap that may be able to remove on the left side. If so, maybe put a piece of hose into the forward left corner & use a pump to pull it out. Suggest you not try to siphon it by mouth. I swallowed a LARGE mouthful of gasoline doing that.

Perhaps you could weight the boat so that the forward left corner of the tank the lowest. I think most pick up tubes are not right on the bottom of the tank. So if you are picking up water, there may be a fair amount of water in the tank. After removing the tank cap, you may be able to see any water rolling around in there?

A good filter/separator should catch any water or debris? "Should" is the key word. :D

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It's probably not as much of a mystery as you would think.

IMHO it is probably nothing more than a failing oil pressure sender unit. This is quite common - I have had it on my own boat and recently had exactly the same thing on the wife's car. On the boat it went on for a few years getting gradually worse. On the car it went from normal to "no pressure" in about a month.

As the engine warms up the resistance in the sender changes and indicates lower and lower pressure but never sets off the buzzer. That's because the buzzer has its own sender and doesn't use the signal from the gauge sender so is sensing the "real" pressure which is probably normal.

For the cost of a new sender unit, the peace of mind is worth it.
Also, a mechanical gauge should be fairly reliable.

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Yes it would but that's a whole new project . . . . where would I put one on my boat? Don't actually know.
I have installed a steel "T" fitting in the original sender hole, one side for the electrical sending unit, the other side for the small, what appeared to be plastic or nylon, hose that went to the mechanical gauge.

Or, one could just temporarily hook up the mechanical gauge to verify the accuracy of the electric gauge.

IIRC, I think I have read about mechanical & electric gauges operating on one sender.

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Hey Paul, without wanting to pull the ring out of this, it's not about the connections to the engine, that's the easy part.

It's about where to put the gauge. It's not going to fit the original panel - or let's say it certainly won't on a Yanmar panel, maybe it will on a Universal's panel.
Ah, understood, space. One thing always seems to lead to another, turning into a big project. :)

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I actually think that the solution on my boat is better. There is a hydraulic high pressure hose screwed into where the oil pressure switch would normally go, and this is run to a bulkhead in the engine room. There is a "T" fitting on the other end of the hose, on the bulkhead, and an oil pressure switch, and oil pressure sender on the T. This reduces the mass connected to the vibrating engine by a pressurized T fitting, and isolates the switches from the effect of vibration.

Here is an OLD picture, in which you can see the hose, pressure switch, "T", and sender to the right of the OLD Sea Ranger battery charger (now gone);
Interesting setup, however one more "link" in the puzzle? I can't see how the supply hose is secured to the T or the engine, but it would be good to inspect it often. I worked on 2 VW diesels, installing gauges in both of them using steel T's, which I checked often for signs of fatigue. After 3 or so years of use they were sound, even after taking a wrench to them.

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I went down to the boat today to prepare for my upcoming 4 day cruise (leaving Saturday). I checked a bunch of stuff on board, and assembled and inflated the RIB. Upon returning home, I found that FedEx delivered the new sender while I was away...:mad:

I sure hope that the old one is 1/8" NPT.
IIRC,I think they make metric to NPT adaptors, if needed? A shop specializing in hydraulics might stock them?

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It's been a month, and TWO senders later, everything is fine. The first sender was a generic JEGS sender that looked right, but was the wrong resistance. The needle on the gauge never rose above 0, so I immediately swapped the old one back and left for my cruise. And, the oil pressure reading gradually dropped, as it had before, but never below 10 PSI. I then ordered a Westerbeake 024132 = Sierra / Teleflex 235880 sender, and installed it. Voilla - 60 PSI all the time! There is a slight drop in pressure when I throttle back to idle, but the engine is running fine.

BTW - The fitting IS 1/8" NPT.
Life is good!! Proves that something I always say, but don't always do,

"Try the easy things first", can work. Good to hear, thanks for the feedback.

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I installed a new Westerbeake 024132 Sender ($70) and it failed after about a day of use. I returned it and bought a Sierra OP24301 Sender ($30) and it has been fine ever since. Pressure runs above 25 PSI, although I suspect that it is actually higher.

The sender is a 100 PSI, 240-33 OHM sender. Again, the catalog jockies at auto parts stores are NO help.
Don't know what the pressure specs are for your engine, but 25 lbs may be a bit on the low side? A mechanical gauge, even just used on a temporary basis, should be fairly accurate.

Engine Oil Pressure Test Kit

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I have always installed after market gauges since they replaced them with warning lights.

I used mechanical oil pressure gauges. The only possible risk is for the hose connections to come loose. A temporary test gauge would give you a base line to compare the electric gauge to the mechanical gauge.

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