OK. I'm almost ready to pull my cylinder head and take it to a guy for a valve job. But I have cold feet (about the $600+ valve job, not about me R&R'ing the head).
My original problem was a ticking sound at idle and under acceleration, one cylinder, every other rev (once per cycle).
Then the ticking became a knocking (when listening under the hood).
Then it began to idle very rough, with a vibration at the same frequency as the knock. And the noise was louder even inside the car.
Then it got harder and harder to start, to where it now needs the block heater at +50 deg. F. And when it's running, there are puffs of black smoke from the tailpipe at the same frequency as the idle roughness.
I have done the following:
Diesel Purge (twice).
Cracked the lines to pinpoint problem. Very hard to hear change in clatter; no conclusion.
Last summer: Tested all the injectors. They were all at 130-135 bar with good pattern, except for one that had a bad pattern. (These were all FastLane reman installed @ ~80k, five yrs. & 40k ago.)
Bought a reman injector from FastLane, tested it, 135 bar, good pattern. replaced the questionable injector. Still bad knocking, rough idle, smoke puffs, hard starting.
Tried the reman injector in each of the other 3 holes. Same symptoms each time.
Early fall - getting very hard to start: Checked the glow plugs (series system). V and R seemed good on all four.
Used a laser pyrometer to take cyl. head temperatures at idle, adjacent to each glow plug. I don't know how valuable the data are because emissivity is a function of temperature, and also I was guessing at the emissivity, and it's hard to get a steady reading, but no. 3 was about 185 and the others were more like 210. I'm pretty sure of this because I went back & forth a few times.
After all that, I took it to Frank of Frank's Service in Lansing, who is pretty well-known with 35 years of doing nothing but M-B service, mainly Diesel. Frank checked compression and found it low in no. 3 and way low in no. 4. I don't remember the exact numbers. He did a leakage test and determined that the source of the low compression was valves.
So now I am ready to take the head in for a valve job, but I am wondering if that is all I need.
First off, I never realized that the way I have always had to start this car is an indication of maybe some other problem. I have always put the pedal to the metal to start it. A co-worker who worked quite a few years for a Diesel injection shop asked me about start-up, and when I told him this he said that's all wrong, and that I should never have to touch the pedal. So I tried to start the car without the pedal (it was warmed up at the time) and it just cranked and cranked. I realized that I probably tried to start it that way when I first got it seven years ago, because I read the manual, but that I had made the pedal a habit, since the car wouldn't start any other way.
Secondly, before pulling the head today, I decided to double-check valve adjustment. I have only put about 100 miles on the car since Frank checked compression.
All of the valves were tight as follows (X 0.001"):
Spec: I = 4, E = 12
Intake: #1 = 3, #2 = ~3.5, #3 = 3, #4 = ~2.5
Exhaust: #1 = 10.5, #2 = 10, #3 = 11, #4 = ~9 or 10? (I only have 0.008", 0.011" and 0.012", no 9 or 10).
So these values made me think that the valve adjustment could be the cause of the low compression.
So I adjusted all the valves spot-on and started the car, w/o block heater. Ambient temp. was about 50 deg. F.
It was a bear to start, it took the usual full fuel pedal, and when it finally came to it was knocking, puffing, and running rough as ever, even after it warmed up. So I am concluding that the valve adjustment did not affect compression pressure.
After it started, I took a length of 3/4" rubber hose and listened all around the head and cam cover. The knock seemed really apparent when I put the hose over the head bolt adjacent to #2 cylinder. I only seemed to hear a whirring with the hose over the other three head bolts. I went back & forth a few times.
So what I am wondering is:
a) Could the somewhat tight valves alone, as quantified above, cause the low compression Frank recorded, and thus I should hold off on the valve job?
b) Could low compression cause a knock? It seems like it would just be responsible for the rough running, hard starting, and puffs of black smoke. The apparent location of the knock near #2 would seem to indicate another problem causing the knock, since 3 & 4 were named the culprits for the low compression. Maybe this other problem is tha cause of the rough running, smoke, and hard starting also?
c) The car started and ran great for the first five years I owned it (bought it in '98 with indicated 70k miles - now has indicated 120k), but it always needed full fuel to start. What might cause that? Injection pump? Timing? Glow plugs? Bad injectors?
As always, any advice is appreciated.
After I fix this thing I'm selling it. Too much work for a one-minute quarter mile and max. 85 mph roaring to beat the band.

__________________
Now you're suckin' Diesel!

'88 300SEL
'92 300D 2.5 Turbo
'96 Lincoln Town Car. The Jazzmobile.

Why would you rework the head before selling?
Unless the car is perfect; seems you are throwing away money.
If Frank says the valves are the problem, take his diagnosis as fact.
Now; if you plan to keep it, the rework has good logic.
Sounds almost as if you would like to keep the car, if it would run right.
I am local, if you want to talk over coffee.

__________________
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Thank you, Hunter.
I figured Frank knew what he's talking about. I can tell by visiting his shop that he knows his stuff.
Anyway, I will answer your question, then can you please answer mine? Thanks.
Maybe I shouldn't have the valve job done; I would like to know how much the car is worth when it can barely be started, runs rough, puffs smoke, and makes a loud knocking sound, vs. running great with a fresh valve job (assuming that's all it needs).
The car is a US-model 240D automatic, has hardly any rust, very nice original powder blue paint, immaculate interior w/dark blue MB Tex, and no other mechanical problems. It shows 120,000 miles. You indicated when I spoke to you on the phone that it could have an odometer lapse, as valve trouble would be unusual at 120k, but I'm assuming correct mileage since that is what was notarized on the title when I bought the car.
The work was going to be ~$1000 with Frank pulling the head, but he said I could save "quite a bit" if I R&Rd the head, so I'm guessing $650 or $750.
Anyway, I would still like an answer to my questions:
b) Could low compression cause a knock? It seems like it would just be responsible for the rough running, hard starting, and puffs of black smoke. The apparent location of the knock near #2 would seem to indicate another problem causing the knock, since 3 & 4 were named the culprits for the low compression. Maybe this other problem is tha cause of the rough running, smoke, and hard starting also?
c) The car started and ran great for the first five years I owned it (bought it in '98 with indicated 70k miles - now has indicated 120k), but it always needed full fuel to start. What might cause that? Injection pump? Timing? Glow plugs? Bad injectors?
As an update, I think I answered question (a) by adjusting the valves spot-on and still encountering very hard starting, noise, and roughness.
I also may be on my way to answering (b) because I did a cylinder cut-out test today and it seemed like the noise only went away completely when I cut out no. 4, which is the one with way low compression. Maybe low compression can give combustion conditions resulting in a knock? Or could it be the ball thing in the pre-chamber broken loose, in addition to the low compression? Note again that the knock is heard during idle and acceleration only, so I think (?) that rules out rod knock.
Maybe I'm closing in on an answer to (c) as well? I'm thinking that maybe the compression has been less than healthy ever since I got the car, causing the full-fuel requirement for start-up, and it merely went from bad to worse recently?
Let me know what you think.
Thanks again.

__________________
Now you're suckin' Diesel!

'88 300SEL
'92 300D 2.5 Turbo
'96 Lincoln Town Car. The Jazzmobile.

US-model 240D automatic, with rust, Michigan title = $1000.00 too $2500.00 if it has a good engine / drive train.
Rust + bad valves + interior wear + paint wear = reduced value.
240D is not a hot sale vehicle, ask other forum members.

As I stated, if you like it, put the money into repair and keep it.

Frank told you what is wrong, you seem to be rejecting his diagnosis.
I can do nothing but repeat what Frank said.
Further testing is a waste of time, money and energy, until the valves are repaired...

Thanks man.
No, I don't doubt what Frank said, I was just wondering if the knock could be some additional problem, because the head work is major enough.
No, I don't want to keep the car. It really isn't well-suited to doing 80mph day in & day out on my 100-mile round-trip commute. I liked it until I started doing all this Interstate driving.
Nonetheless, I am going to pull the head and have Frank do his thing. I will at least get some of that dough back when I sell it, and I will feel better selling it. Plus I will at least have a reliable daily driver while I look for a choice 300D Turbo or a 300SD or SDL. Or maybe a Porsche 914 2.0, but I don't think I want to make that my daily driver; I would like a nice one as my toy.
Thanks again.
Ted out.

__________________
Now you're suckin' Diesel!

'88 300SEL
'92 300D 2.5 Turbo
'96 Lincoln Town Car. The Jazzmobile.

Somebody on here was asking what a 240D with 67k is worth that had everything good except the transmission would not go in reverse. I also saw a 240D on here for sale for $500. You might want to see about getting one of these cars and swapping a motor or transmission. If the car has had bad compression for a long time then it would of been putting a lot of soot in the oil, which is hard on the bearings due to the acidity of the soot. How much oil has you car been using?