This car (1982 300D) had this knock ever since I bought it. I replaced the injector nozzles, I loosened the fuel lines one by one, the knock persists.

The engine does not smoke at all, and at 1000rpm it is very smooth. It does have a vibration at 650 rpm, not loping, just kinda vibrating more than I'd like.

I did the following (engine related) work on it so far, in addition to the misc stuff like new drivers side seat

- air cleaner mounts
- blowby drain tube
- injector nozzles
- motor mounts and engine shocks
- timing chain stretch corrected
- valve adjustment
- new spring for the chain tensioner


I finally took it to a local foreign car mechanic for a look, just to keep the project moving, so to speak. I didn't expect a miracle (and didn't get one). Just wanted a second opinion.

After having the cover off, here is what he told me:

- the knock is definitely coming from cylinder #1
- the knock is definitely coming from "top", i.e. head, not crank
- everything under the cover looks good; camshaft looks great, nothing obviously worn or loose
- the cylinder pressure is 340 or something like that, so its good
- fuel pressure is good
- probably not a worn or loose valve guide because NO smoke
- probably not piston slap because NO smoke

He does not think it is broken rod or rod bearing because we both had the car on the highway and it still runs.

The knock sounds like its just about once per engine revolution.

Naturally, I wanted options. He said the next logical step here would be to pull the head and inspect the bottom of the head and the top of the piston.

His working theory now is something fell in the cylinder - a piece of a glow plug or broken precombustion chamber, or maybe even something through the air cleaner.

I don't mind pulling the head off and spending time on it. I have a beer fridge in the garage, so its all good times. Should I stick with it? How likely is pulling the head to uncover the cause? Any words of encouragement?


here's the link to the clip with the sound it makes:
http://www.youtube.com/watch?v=s2pEM3fAepw

ever use a stethoscope and poke around to pinpoint the area?

If some thing had fallen or broken in the combustion area i think your engine would be toast

__________________
1986 300SDL, 211K,Dealership serviced its whole life
1991 190E 2.6(120k)
1983 300D(300k)
1977 300D(211k)

Yeah both he and I used the stethoscope. He says 1st cylinder, upper area (head, basically)....

Where the injectors properly pop tested and balanced? Although I suppose that'd go away with the injector line cracking.

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1983 240D 3.0T 4-speed manual, now sold

1989 Subaru GL Wagon 5-speed Touring Edition

They were not but its not an injector noise; it is clearly mechanical. And you are right, the sound does not go away with opening any of the lines....

Would it be of any benefit to pull the oil pan before tackling the head, to see if there is anything in the pan?

Pull the injector and look in the hole. The ball in the prechamber could be broken or the end of the prechamber could be burnt off. Pull the prechamber and look in that hole it is a lot easier than the head to start. You should not be able to get a straw into the cylinder past the prechamber end the holes are radially out. Check the vacume pump bearing.
I have a small led light that will go in the small holes so I can look around.

Hope this helps
Robert

ok will pull the injector and the pc...

Did you try swapping say number 5 injector with number 1 & see if the noise moves?

__________________
Grumpy Old Diesel Owners Club group

I no longer question authority, I annoy authority. More effect, less effort....

1967 230-6 auto parts car. rust bucket.
1980 300D now parts car 800k miles
1984 300D 500k miles
1987 250td 160k miles English import
2001 jeep turbo diesel 130k miles
1998 jeep tdi ~ followed me home. Needs a turbo.
1968 Ford F750 truck. 6-354 diesel conversion.
Other toys ~J.D.,Cat & GM ~ mainly earth moving

Yes, I did do that, before I did the nozzles...

Ok, I counted the knocks, and I get 64 knocks (for some reason they are real easy to count in multiples of 8) in 9.6 seconds.

That works out to about 400 knocks a minute. If I am off by about 1/2 second, this is about +/- 20.

The car idles at about 700 - 800 rpm.

Roughly, my knock happens once about two revolutions i.e. once per complete cycle.

So, it could be happening, for example, during power stroke of my #1 cylinder, which could be some looseness in the rod bearing.

Or it could be happening on exhaust stroke at the top, if the ex valve interferes with the piston...

Thoughts?

Wouldn't that be twice every complete cycle, ruling out a powerstroke problem?

__________________
1977 300d 70k--sold 08
1985 300TD 185k+
1984 307d 126k--sold 8/03
1985 409d 65k--sold 06
1984 300SD 315k--daughter's car
1979 300SD 122k--sold 2/11
1999 Fuso FG Expedition Camper
1993 GMC Sierra 6.5 TD 4x4
1982 Bluebird Wanderlodge CAT 3208--Sold 2/13

Power stroke in each cylinder happens every 2 complete revolutions of the crankshaft... thats what I meant...

if loose rod bearing , the noise would be down lower & should give some noise every rev.
I have heard a similar noise from a cracked piston.
A comp test may give a hint.
Could even be a cam/valve problem.
Does the noise go away at running revs/highway speed with some load? Did the noise just start one day or has it been there for a while? Is it getting louder with time?

__________________
Grumpy Old Diesel Owners Club group

I no longer question authority, I annoy authority. More effect, less effort....

1967 230-6 auto parts car. rust bucket.
1980 300D now parts car 800k miles
1984 300D 500k miles
1987 250td 160k miles English import
2001 jeep turbo diesel 130k miles
1998 jeep tdi ~ followed me home. Needs a turbo.
1968 Ford F750 truck. 6-354 diesel conversion.
Other toys ~J.D.,Cat & GM ~ mainly earth moving

I do not know the configuration of you fan belt tensioner, but in my car, I swore that I had an internal engine knock, with the same sound you are describing. After racking my brain for two days, it turned out to be the belt tensioner shock hitting against the engine block at its mounting point. The bushings had gone bad, and the noise was very prevalent at idle, and would disappear at higher rpms. All I had to do was put my hand on the shock, and the noise was gone. Easy fix for me, and I hope it turns out to be the same for you.

__________________
96 E300d

Good compression all 5 cylinders. I dont have the #s handy but I had it checked (I do not have the test equipment so I took it in for that)

Somwhat... The noise is MOST quiet (almost gone) when exiting off the interstate or generally slowing down from going at 50-60mph. Then it is almost a perfectly purring engine.

Always been there but I've only had the car for 6 months and put maybe 80 miles on it. Its been a 'garage project'...