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Discussion Starter #1
My engine (1982 Universal 5432 diesel, 1650hrs, 32hp, 4cyl) has developed a loud knocking/slapping sound since my last oil change. I first thought I must have overfilled, but it doesn't seem to be the case -- maybe just a red herring. I had a mechanic look at it and he found that one of the injectors had stopped and the others were in bad shape (P/O had never serviced them). The nozzles were wet with either fuel or oil. The injectors have been fixed but I'm still getting the noise.
I also get soot coming out of the exhaust when I put the engine in high revs. My mechanic suspects bad piston rings and wants to pull out the engine ($$$), but doesn't have strong evidence to support doing this other than an educated guess.

Any suggestions? Could be carbon buildup? Could I use an additive cleaner?

Cheers,
- Stu
 

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midlife crisis member
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Could be high compression due to soot buildup in the combustion chamber (caused by poor running with bad injectors). The high compression could be causing preignition which would give you a knocking sound.

The mechanic should be able to do a compression check while the engine is in the boat which would verify or eleiminate the rings being the problem.
 

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midlife crisis member
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Also make sure the mechanic put in the right oil the last change. It may be worthwhile to do another oil change to see if the problem goes away.
 

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A belt outer cover coming off and slaping something?
When were the valves adjusted?
Does the noise change when in gear?
Does the noise change with different loads?
Does it change with rpm?

Rick
 

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When did it start?
Is it getting louder?
Are all the accesories still bolted on tight?

Rick
 

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the pointy end is the bow
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I would get a mechanic's stethascope to see if I could locate the source of the noise, then start troubleshooting from there. You can use a long screw driver too. One end on the motor, the other end against your ear.

clacking sound, valve train
knocking noise under load, main bearings
knocking noise when reving, rod bearings.
tinking noise, wrist pins
 

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Mud Hen #69, Mad Hatter
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I like the pre-ignition suggestion. Carbon build-up glows when hot in a cylinder and can ignite the fuel as it is sprayed in, causing a "knock" or "ping". In a diesel it can sound like someone rattling a a stack of dishes.

Try this. Rev it up to full rpm under load and shut down the throttle quickly to 1/2. If the rattle stops it's pre-ignition. If it keeps up but at a slower rate it could be a mechanical problem.

A fuel knock could be something as simple as poor quality fuel or a plugged fuel filter (or bad injectors) or timing needing adjustment. This is one case where a vacuum gauge on the filter is handy as all get out.

Could also be a worn piston , piston pin, bearings - all kind of bad news.
 

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Irrationally Exuberant
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Did it really start right after that oil change? Last thing done is usually the first suspect, even when it seems unlikely. You did this oil change yourself? As someone else asked, was the correct oil used?
 

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Discussion Starter #9
Thanks for the ideas. Here's some answers to the questions:

I changed the oil myself and used Delo 400 LE 15W40 -- the same grade as listed on my last oil analysis in December (my user manual calls for SAE30HD/10W40). I checked with the P/O about overfilling. He used to keep the level at the dipstick's high-mark (I refilled part-way between low and high). I think this pretty much rules out overfilling as a possibility. (The reason I thought is might be relevant is because my mechanic flipped out when I told him that I though my engine takes just shy of 3 gallons of oil -- which it does.)

There's nothing loose on the exterior of the engine as far as I can see (I have good access all around). I get the slapping noise whether in gear or not. RPM seems not to be a factor (almost no sound while idling, noticeable at >1000rpm and louder as the rpms increase). I don't remember load being a factor (noise is present whether in neutral, forward or reverse.) As far as I can tell the noise seems to come from the top of the engine. I'll try the screwdriver in the ear trick and see how I get on.

I can't say for sure when the problems started -- around the time of the last oil change (I have 8 hours since the last change). I also refueled around that time too. It definitely seemed to be getting louder over time -- its what prompted me to get a mechanic. Another possibility: when I replaced by Racor filter (quite a long while ago), I topped off with diesel from a gas station (bad diesel? should have strained the fuel I used?).

My mechanic found that one of the injectors had failed and the others were in bad shape. He replaced all of the nozzles and one of the fuel lines, but the slapping remains. I wish he'd done a compression test. Unfortunately he didn't think it was important. I have a friend who has a kit. We may be able to do a test if we can get the correct adapter.

Currently the exhaust is mostly white. Looks like there may be some oil in it. It thins out quite a lot when the engine warms up. Mostly it smells quite heavy -- like there a lot of fuel in it.

Last weekend we took the rocker cover off and measured the valve clearances. We found that some of them were 3x the clearances specified by the manual. Reducing the clearances didn't seem to do much to reduce the noise. Rapping on the top of the valves seemed to reduce the clearances too (suggests knocking off carbon buildup?). We're a little nervous about reducing the clearances much (if carbon buildup is the problem, and more carbon falls off, there may be no clearance left - could cause valves to stay open. Could this cause permanent damage?).

We also found there was a little blow-by (but no oil in the re-circulated air).

Next weekend, I'm planning on changing the secondary fuel filter and making the valve clearance to spec to see if that help.

I've also found a fuel additive at Kragen that claims to help remove carbon buildup in diesel engines. Anyone ever tried this?

Cheers,
- Stu
 

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Whoa- 3 GALLONS of lubricating oil??? should be about 5-7 quarts. I found one source that lists total capacity as 11.5 quarts but I am unsure if that is correct. if so, adding 11 quarts (nearly three gallons) at an oil change should have your dipstick level at or above full level. Something ain't right here.
 

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Discussion Starter #11
My manual listx 11.5 quarts. 2 gallons is what we got out at the last oil change - at that time the level was at the low mark on the dipstick. 10 quarts is part way between the low and high marks. It really does take that much oil.
Its a monster that needs to be fed.
 

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You should not run the the new auto fuel in your engine.

You don't have the necessary electronic fuel control for it.

How much did you add to how much?

Just shy of three gallons sound like 11.5 quarts to me.

To tight valves will burn the exhaust and cause a back fire in the intake.

To loose valves will cause a loss in compression and hp.

I say adjust the valves and check the clearance after about an hour of running. Just stick the gasket to the cover and grease the side going tothe engine and it should come right off and go back on without any trouble.

Get rid of the poluted fuel.
 

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Discussion Starter #13
You should not run the the new auto fuel in your engine.
You don't have the necessary electronic fuel control for it.
How much did you add to how much?
I added about a cup of gas-station diesel to top off the Racor when I change the filter. That's it.

I say adjust the valves and check the clearance after about an hour of running. Just stick the gasket to the cover and grease the side going to the engine and it should come right off and go back on without any trouble.
I'll give it a try.
Thanks.
- Stu
 

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STARBOARD!!
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To loose valves will cause a loss in compression and hp.

I say adjust the valves and check the clearance after about an hour of running.
I don't think his valves were that loose. He had two valves that were way out @ 0.020 which we adjusted back to nominal (.008). The others were at 0.015-0.016. The amount of lift is much much more than the clearance; the loss of duration should not be enough to cause compression loss IMHO. With such loose clearances I was concerned with carbon deposits holding the valves open so we tapped the valve stems with a small hammer to try and get the suspected carbon deposits to smash away from the seats. I always do this first on engines that need clearance adjustment that are showing loose clearances because typically the valve clearance should become less over time; not more. There was very little if any change in the valve clearance on the valves that we tapped on.

One thing I think we should touch on is that the boat did not display a problem before the oil change; but we can't rule out the existence of it before that time either. It's possible that the engine oil that was in it prior to Stuart's first oil change was a much heavier grade to help prevent the oily soot and/or alleviate the rod knocking noises. We just can't say for sure but that is one possibility. The problem it has now (I think) is failed rings on the #3 cylinder and possibly worn journal bearings resulting in the knocking noise. Unfortunately if that's true it is time for a rebuild or re-power.

Stu-

In reading this thread; there was a post that mentioned hard carbon deposits causing a hot spot and pre-ignition. While I don't necessarily this is the whole problem; I can't rule it out. What concerns me more is the heavy smoke you are getting now that the #3 cylinder is getting proper fuel flow. It looks like it is not getting adequate compression until the engine gets warm enough to help it fire with improved adiabatic temperature/pressure. I think that's where your mechanic decided your problem was more than a minor issue also. If you want to do the compression test, let me know and I will get the tester that Harbor Freight has for "Kubota" engines on Friday. We might be out sailing one day on Sat or Sun (weather permitting) but I could help you look at it on the other day.
 

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Watkins 23
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I will preface what I say with the disclaimer that I don't have much experience on marine diesel. However, I have some experience on highway and farm diesels. I would consider pulling the injectors and taking a look. You said the mechanic put in new nozzles, not new injectors. I have seen properly torqued nozzles leak badly. The smoke (even white before the engine is up to temp) can look a lot like broken injector nozzle. Another possibility. Does this engine have a timing chain as opposed to gears? If so, the chain could be loose. (Some engines also use a hydraulic tensioner which, if worn, could fail. Don't know if yours has this but I have an antique Merz that does. An oil change might be a good time for that to show up a problem.) A loose chain will make a slapping sound and throw the timing out making for smoke, carbon, then excessive compression and the pre-ignition that goes along with it.

Just a couple more suggestions to throw into the mix.

Richard
 

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I found a quick troubleshooting step is listen to the knock, then put in ear plugs - if you continue to hear the knock it's not a click/clack light vibration - it's a solid hit meaning rod bearings or some other major machanical malfunction. The ear plugs will filter out the high vibrations from loose equipment, pinging, pushrods and other non-critical sounds the engine may make.
 

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Taking into consideration the information provided..... I would check that if you changed the oil-filter when you changed the oil - that you used the correct oil filter. The slapping sounds as though there isn't enough oil to effectively lubricate working surfaces.
(my two cents)
 
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