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Discussion Starter · #1 ·
OK Diesel engine gurus, I have a puzzle...

I have a 1987 Universal M25 with unknown hours, but the hour meter was installed about 395 hours ago. When I bought the boat, four years ago, it showed 175 hrs. The engine has a tendency to drop oil pressure when warm (drops from 45 to 10 PSI after several hours of running), but never overheats, and oil pressure never goes low enough to set off the alarm.:)

I recently installed three new injectors, and all seemed well until yesterday.

Yesterday, there was little wind on Narragansett Bay, so we motored for about 4 hours down the West Passage to Wickford. We had a nice lunch, then motored out, and raised the sails, as the wind had piped up... After making our way back up the East Passage, and passing Bristol Harbor inlet, the wind died again, so I fired up the engine again.

We ran the engine for about an hour at 2700 RPM, when suddenly it started knocking. I quickly throttled down, and the knock changed frequency. All the gauges looked normal (Oil @20 PSI, Water temp @180, Voltage @14+) I popped it into neutral, and the knock persisted. I looked over the transom, and noticed smoke (white - possibly grey) out the exhaust. I went below, and opened the engine compartment, but could not locate the source of the knock, so I shut it down.

I checked the oil - warm but the level was OK, looked for leaks - none, looked at the coolant overflow - OK. There was some oil that had escaped from the breather tube, but not a lot, and it really isn't that unusual. Because I could find nothing amiss, I started the engine again, and the knock was gone! We safely motored back to the pumpout, and then the slip (about another hour) without a problem.

What happened?:confused: What should I look out for? :confused:
 

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Discussion Starter · #8 ·
Get a copy of your engines Repair and Maintenance Manual (aka - "Shop Manual') and verify your injection pump timing.

Grey 'smoke' coming out the exhaust is usually a sign of either 'over-fueling' / unburnt fuel and mostly is caused by incorrect engine timing; but, can be caused by low compression.

If the timing is found to be correct, then look for broken / sticking piston rings or an exhaust valve that is cracked or not making a complete seal with its valve seat ... or is simply 'hanging up' (not making its full 'stroke' ... such can be caused by a pin hole water leak inside the exhaust manifold, etc. 'back draining' into a combustion chamber when the engine is shut down), etc. etc.
Then I would suggest that you do an 'air pressure leak down test' of the combustion chambers (instead of or in addition to a compression test). With the injectors removed, High pressure air is put into each combustion chamber with each piston in turn at bottom dead center, and you look for 'where' the air is leaking out of: - crankcase breather (broken/sticking piston rings), exhaust system (ex. valve problem), air intake ( intake valve problem), into the cooling water (blown head gasket), out of an adjacent combustion chamber (blown head gasket), etc. etc.
Verify your injection timing FIRST, as on most small diesel engines the injection timing should be checked about every 500-750 engine hours as a routine 'maintenance item'.

hope this helps.
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:

E, isn't 2700 rpm too high for that engine?
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.

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?
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?)...
 

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Discussion Starter · #10 ·
Good guess Denise,

Been there, done that three years ago, when I first noticed the oil pressure strangeness.

The check valve on the M25 is above the oil filter on the starboard side. IIRC, it is a 19MM hex head, which you can back out to clean the passage, and the ball bearing.
 

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Discussion Starter · #11 ·
Here is some context on WHY I replaced the injectors; http://www.sailnet.com/forums/diesel/92290-universal-m25-losing-power.html

Also, because I tore my ACL in early May, the boat has been sitting in her slip until about a week ago (2 months). The bottom has not been cleaned, and I suspect a very dirty prop and bottom.

Finally, the reason for my concern is that I am heading out for a week long cruise with some friends in 3 weeks. Thus, I have three weeks to diagnose and address an intermittent problem.

Thanks again to all who help!
 

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Discussion Starter · #15 ·
Thanks Stu,

I am pretty sure. The knock persisted in neutral, and varied with the engine RPM. Also, the exhaust had white/grey smoke, almost like a cylinder wasn't firing. I took the boat out on Tuesday, and it did the same thing. It knocked after a couple of hours of run time, so I quickly shut it down. When I restarted it, the knock was gone.

I went down to the boat yesterday, and stopped at Harbor Freight on the way. I picked up a diesel engine compression test kit for under $30, and tried it out on the engine. It is not a great tool, but it will do what I need. The gauge is marked in 20 PSI increments from 100 to 1000 PSI.

I started by adjusting the valves to 0.0062 IN. It seemed to me that Cylinder 2 was way out of spec.

Here is what I found with the engine stone cold;
  • Cylinder 1 - 380 PSI
  • Cylinder 2 - 360+ PSI (I'd estimate 365 PSI)
  • Cylinder 3 - 380 PSI

Finally, since the raw water intake was shut off, and because I hadn't checked the zinc since she was launched on May 9, I checked the zinc. It was time to replace it.

I'll take it out today, and let you know if I addressed the issue.

Thanks to all for their help! :)
 

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Discussion Starter · #16 ·
OH - BTW, you DO NOT need to see the timing marks. I borrowed a borescope from a friend, but found it not helpful. I simply rotated the flywheel to where neither of the valves were open on the cylinder that I wished to test. As long as you are on the flat of the cam, you are good to test.
 

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Discussion Starter · #18 ·
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.
 

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Discussion Starter · #20 ·
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.
 

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Discussion Starter · #22 ·
This O'day 35 has the original 1986 Florida Marine Tanks 35 gallon tank;


I use about 20 gallons of diesel per year, and always top it off from my marina before winter layup, so it has never been fully drained. I tape the vent closed, and close the fuel shutoff during winter layup.
 

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Discussion Starter · #31 ·
I think that's one of them Tadslack steering systems.
That pic was taken 4 years ago; before I removed the steering quadrant and dropped the rudder so that I could replace the cutlass bearing and prop shaft. Upon re-installation, everything was tightened appropriately.

If you were to see this view today, you wouldn't recognize the place, except for the original, oxidized, fuel tank.:)
 

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Discussion Starter · #32 ·
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.
THAT makes perfect sense! It is quite unnerving to have 50 PSI at the outset, and < 10 after about 3 hours motoring...
I'll be installing a new sender soon!
 

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Discussion Starter · #35 ·
The new sender is on order from Amazon...

What happened to when employees actually had to know something about auto parts? I stopped at Pep Boys, AutoZone, and Advance Auto, and they all ask what kind of car. "It's not for a car...." Then we can't help you. Bottom line is if they can't look it up in a book, they're not interested in helping you out.
 

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Discussion Starter · #40 ·
T'ing the output at the engine block is the way to go. The little oil line can be short and run to a gauge close to the engine,(not on it due to vibration) The other side of the T holds the electric sender. If you trust your new sender the T can go to an off/on sender for alternator field and a solinoid to drain/prevent filling exhaust riser.
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);
 

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Discussion Starter · #42 ·
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.
 

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Discussion Starter · #44 ·
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.
 

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Discussion Starter · #48 ·
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.
 

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Discussion Starter · #50 ·
Ya, I don't trust the electronic gauge either. Based on the short stint that the OEM gauge worked, I believe that it is actually running about 50 PSI.
 
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