Slapping sounds from engine

[stuffinbox]

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

[AllThumbs]

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.

[AllThumbs]

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.

[timebandit]

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

[timebandit]

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

Rick

[erps]

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

[Delirious]

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.

[arf145]

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?

[stuffinbox]

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

[bljones]

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.