I was going to try adjusting the rack damper bolt but I'm not sure how to go about it.

There are no threads visible. It appears that the nut is tight up against the bolt head and the bolt screwed into the IP all the way.

I looked at my other 300TD and it is the same.

Which one is the lock nut? the big 14mm nut against the IP ot the smaller 12mm bolt head on the end?

Attached Thumbnails

 

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1987 300TDT
1981 VW MKI Caddy 1.6 diesel, waiting on engine swap
1983 D-50 Power Ram 4x4 "Mitsubishi" 2.3 turbo diesel
assorted gas powered crap and motorcycles

RIP: 1984 300TDT, 1982 300TDT, 1984 190D 2.2, 1992 300D 2.5, 1987 300TDT, 1982 Maxima LD28, 1983 Maxima LD28, Isuzu C223 P'ups X3, 1983 Holiday Rambler 6.2 Banks turbo diesel, 1984 Winnebago LeSharo 2.1 TD, 1985 Allegro 6.5

the outer bolt heat is the one...the inner one is a jam nut.

Is it gold or silver?

It should not be all the way in....only enough to stop surging....no more, no less.

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Proud owner of ....
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1979 300SD W116
1983 300D W123
1975 Ironhead Sportster chopper
1987 GMC 3/4 ton 4X4 Diesel
1989 Honda Civic (Heavily modified)
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Section 609 MVAC Certified
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"He who fights with monsters might take care lest he thereby become a monster. And if you gaze for long into an abyss, the abyss gazes also into you." - Friedrich Nietzsche

They do wear out. The old style was silver and it was replaced with a gold model that works better.
If it is in to far when the engine is rev'd up and then allowed to drop to idle it will stumble, sometimes die. That is when you know you have it turned in too far. Another way is that the car won't keep dying at every stop, or it will not have enough power to leave the yard.
If it runs ok but has an idle miss it can sometimes be cured by adjusting the fuel rack damper bolt. Most times they appear to be in most of the ways. Only way to tell for sure is to break the tighener nut and turn it in further. If you take it in all the way and it makes no difference you may have a candidate for a new damper bolt. Check it i good light, if it is silver color just order a replacement, if it is a light gold tome, it may be that you have other problems, or are not adjusting it right. Like he said, just in enough to stop the idle lope, or idle surging.

I replaced the rack damper bolt and it runs best screwed all the way in! If I turn it out the idle gets rougher and rougher. All the way in is nice and smooth, plenty of power and no dying. I suppose the spring in the pump is shot but I will tackle that when it becomes an issue. RT

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When all else fails, vote from the rooftops!
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I went outside and looked at it again...

I can't really tell what color it is. It seems to have a lot of oxidation or whatever. I would guess that it's probably original.

It is turned in all the way for sure. Not even a tiny gap. The lock nut is tight against the bolt head.

Just how much play or adjustment is there supposed to be? When a new pin is installed, how many threads should be visible? One, two, more? How long is the rubber part that wears down over time?

__________________
1987 300TDT
1981 VW MKI Caddy 1.6 diesel, waiting on engine swap
1983 D-50 Power Ram 4x4 "Mitsubishi" 2.3 turbo diesel
assorted gas powered crap and motorcycles

RIP: 1984 300TDT, 1982 300TDT, 1984 190D 2.2, 1992 300D 2.5, 1987 300TDT, 1982 Maxima LD28, 1983 Maxima LD28, Isuzu C223 P'ups X3, 1983 Holiday Rambler 6.2 Banks turbo diesel, 1984 Winnebago LeSharo 2.1 TD, 1985 Allegro 6.5

if it is original and not the upgraded gold headed bolt , don't adjust until you obtain one. This is a very important update and the
adjustment of the rack damper bolt is very critical. It
should just barely make contact and damp the shake (when
EVERYTHING is running correctly and the engine is WELL
warmed up) then loosen it 'til it shakes - then tighten 'til
it just stops shaking. Then tighten it down. I played with mine over several days
Pretty scientific huh

How does the rack damper bolt work exactly? I've messed around with mine, and adjusted it, but it just doesn't seem right. Mine is the old style so it might just be worn out.

My SD has pretty rough idle. The engine vibrates quite a bit, especially when warm. Revving it up slightly makes the vibration go away, it gets rock solid. Adjusting rack damper bolt/screw/pin was suggested to me, so, well, I screwed around with it, after searching this forum for a while. I did try screwing it in all the way, waiting for the engine to demonstrate any signs of poor health, but it never happened. With the bolt screwed all the way in, I tried starting the car and driving around, and couldn't tell any difference from the previous bolt position, which confused me. Now, when I tried to screw the bolt out, and the engine did start loping wildly side to side past a certain point, as prescribed. So the bolt has some effect, but then I don't understand why screwing it all the way in makes no difference. Thus the suspicion that the bolt may be bad.

My bolt has gold threads, i.e. it's a replacement one. From what I've read, 'gold' bolts do not wear out. The tip of the bolt has some pretty strong spring action. I understand that a bad bolt should have very weak spring action, if any. "Pretty strong" is a pretty subjective term though. Periodically I'm contemplating dropping $40 on a new bolt, because the engine shake is annoying, and the bolt is easy to change, but then I don't believe my bolt is really bad, but I don't know how to tell.

yuri

http://engine.articles.mbz.org/diesel/rackbolt/

Note the advise to have the engine in good shape as far as valve adjust and of course your injector nozzles better be fairly good as far a spray pattern and opening pressure (new ones are not always matched!) - then the damper bolt can do its thing. If other problems are in place then the engine will not balance properly at the normal idle speed (approx 625 - 650 RPM) at SOMETHING LIKE 50 to 75% screwed in. All the way in and its pressing the fuel rack too hard and not meant to be set that tight.

I would not buy another bolt, if yours is the gold colored one and its stiff its probably OK.
Have you checked the engine shock(s) ????

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[QUOTE=dieseldiehard]Note the advise to have the engine in good shape as far as valve adjust and of course your injector nozzles better be fairly good as far a spray pattern and opening pressure (new ones are not always matched!) - then the damper bolt can do its thing. If other problems are in place then the engine will not balance properly at the normal idle speed (approx 625 - 650 RPM) at SOMETHING LIKE 50 to 75% screwed in. All the way in and its pressing the fuel rack too hard and not meant to be set that tight.QUOTE]

I disagree. I just had the head off mine to do the headgasket. Did a valvejob and timing chain guides when it was apart. Had the injectors tested, they were fine. Adjusted valves, twice. New motor mounts and shocks @ 1year ago. Installed new rack damper bolt and it is threaded all the way in. Dead smooth idle. No issues starting, stopping or running. It is threaded in deeper than the old one. My only explanation is maybe the IP is doing something weird. Hard to believe as it has never run better. RT

__________________
When all else fails, vote from the rooftops!
84' Mercedes Benz 300D Anthracite/black, 171K
03' Volkswagen Jetta TDI blue/black, 93K
93' Chevrolet C2500HD ExCab 6.5TD, Two-tone blue, 252K

Sounds like I'm not gonna mess with it until I have a new one in hand, ready to use.

Still waiting on my injector return lines to arrive. Can a leaking injector return line cause rough idle?

__________________
1987 300TDT
1981 VW MKI Caddy 1.6 diesel, waiting on engine swap
1983 D-50 Power Ram 4x4 "Mitsubishi" 2.3 turbo diesel
assorted gas powered crap and motorcycles

RIP: 1984 300TDT, 1982 300TDT, 1984 190D 2.2, 1992 300D 2.5, 1987 300TDT, 1982 Maxima LD28, 1983 Maxima LD28, Isuzu C223 P'ups X3, 1983 Holiday Rambler 6.2 Banks turbo diesel, 1984 Winnebago LeSharo 2.1 TD, 1985 Allegro 6.5

A few points
The bolt must be adjusted while engine is HOT
The bolt serves to "dampen" the movement of the rack in the injector
It is possible even with a new bolt that it will screw in all the way, pumps do wear.
A inline 5 cylider diesel will always have some movement (rock) it is mechanically impossible to completely balance them.
A buddy of mine expalined it this way

Mercedes dealt with this by putting the motor supports at the center of mass and allowing the engine to vibrate. It is quite a bit smoother than the 4 cylinder (OM 616.9xx) but not nearly as smooth as either a straight 6 (M103) or 8 (M117) .

The straight 6 (or 8, 10, 12, etc...) is ideal from a balance standpoint and can be set up so that all primary and secondary shaking and rocking forces sum to 0. A 90 degree 8 can be set up so that each bank has only a primary (at crank speed) rocking couple. These can be set to be 90 degrees out of phase and can then be compensated by eccentric weights on either end of the crankshaft (that's why a V8 has a harmonic balancer, and a straight 6 doesn't.)
Have Fun

Why can't an inline 5 be balanced? If the crank has 5 evenly spaced throws then it can be balanced.

A V-6 can also be perfectly balanced, but that configuration requires a 120' engine. Ferrai built one once. But it was very wide. At that point just go flat-6 (911 & corvair style).

All other V-6 engines are 90' or 60' engines & require balance shafts or huge motor mounts

__________________
1987 300TDT
1981 VW MKI Caddy 1.6 diesel, waiting on engine swap
1983 D-50 Power Ram 4x4 "Mitsubishi" 2.3 turbo diesel
assorted gas powered crap and motorcycles

RIP: 1984 300TDT, 1982 300TDT, 1984 190D 2.2, 1992 300D 2.5, 1987 300TDT, 1982 Maxima LD28, 1983 Maxima LD28, Isuzu C223 P'ups X3, 1983 Holiday Rambler 6.2 Banks turbo diesel, 1984 Winnebago LeSharo 2.1 TD, 1985 Allegro 6.5

What I am saying is that by design the engine will always have a rock, no mater what adjustments you make. Have you had the joy of picking up a crankshaft from a .617
You are correct about the 6 cylinder