I'm reading through the Performance Tuning book from www.**************.com (hope I'm not committing some grave sin of disloyalty here, but his operation is different from this) and have been amassing a list of Fundamental Questions. (The Vacuum Troubleshooting book wasn't nearly so intimidating.)

Btw, anyone who can post clear photos, or direct me to clear photos, that illustrate these things will have my undying gratitude and will have earned a special place in Heaven.

1) What are crank bearings? And it was mentioned they'd be in the "lower end of Diesel engine". Am I thick? Are there a lower and higher ends? They look pretty level to me.

2) What is the rack damper bolt on a 617 engine (that's mine)?

3) What exactly is a "throttle linkage travel"?

4) In the section about engine running temp., he wrote that one should check the "gauge sending unit" or the "thermostat". This confuses me. I've always considered a thermostat a switch activated by a voltage difference in the thermocouple. There's a switch controlling my engine temperature? The coolant was recently changed and I noticed that the engine seems to be running a little hotter (just over 100 C) than it did before the change (just under 100 C) ... which was higher than he says a healthy engine should be running at (80 to 90 C). I'm wonder if the temperature measuring device (whatever it is) is off and needs to be replaced, 'cause I don't think there's a blockage in the coolant system.
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Next two questions are not because of the book.

5) I've noticed that Hilda idles really roughly...well, evenly, but you sure get jiggled a lot....when in Drive and stationary with my foot on the brake. That means at every stoplight. This is much rougher than when starting. Idles less in Neutral or Park, even with the brake on. (Checked that just to be sure.)

6) I changed the daisy chain of fuel return lines between the injectors today and when I pulled the line off between the second from the front and the third from the front, some fuel came out of the line and I noticed that there was fuel in the front tip/nozzle/little-brass-thingammy-that-I-just-pulled-the-line-off-of of the third from the front injector. I put the new line on before pulling off the next on, so I couldn't observe if the fuel went away when I pulled off the line between the 3rd and 4th injectors. I didn't notice fuel in either the next line or in the back nozzle from that 3rd injector. This didn't happen on any other. Is this a problem? Seemed odd.

Any takers?

Tanks!

__________________
Growth for the sake of growth is the ideology of the cancer cell. -- Edward Abbey

1984 300SD: Hilda the veggie vundercar

1. The head is the upper part of the engine.. the block and stuff having to do with the crank is the lower...they meant ' lower half'.
2. The rack damper bolt is provided to allow the setting of the idle to reduce shaking of the engine at some rpm's.....
3. Throttle linkage travel is simply the position of the metal linkage which connects the throttle pedal you push with your foot... to the fuel increasing/decreasing system of the engine ( maybe the governor or fuel injection pump ) compared to the position when pushed all the way in.... this has been the subject of a lot of people finding that when they checked/corrected the travel available they had LOTS MORE POWER... a 20 something year old car can get worn/out of adjustment slowly....and no one expects a diesel to have much power anyway... so it slowly gets to where it has like only 3/4ths of the travel it should....
4. THe thermostat is a physical device in the coolant stream which directs water to the radiator in varying amounts depending on the need of the engine for more or less cooling..
The Guage sending unit is the thermal reacting item screwed into the side of the block which generates electricity in varying amounts which the guage in your dash sees and interprets as different temperatures...
6. No that is not a problem..
5. You really need to address a couple of things if you have a rough idle... check the Tech service bulletins which have been issued for your car by looking at alldata.com
and find the directions for setting the rack dampner...
and read up on setting /checking the engine mounts...

Ps, I think you would really enjoy having the paper factory shop manuals for your car... these are complicated and " over the top' designed cars... I am regularly surprised at how MB did something compared to all the other car makers in the world...

also, the search feature on this site really rocks.... and when something has already been posted you don't have to wait and hope someone will stop by and know the answer....

sohj,

I want a place in Heaven too, maybe then I will actually get to finally meet leathermang since he has already answered your questions pretty thoroughly. I am a little late but typically much wordier than Greg, so as long as my place is within walking distance of his I will be ok.

1. The crank bearings are the stationary supports at the center of rotation for the crankshaft, and MB typically has a set of them (they are normally split rings, with the split at the horizontal centerline of the of the bearing "journal" of the crank support bearings that are captured on the upper half by the structural ribs of the crankcase, and by bolt-on caps that look a lot like pipe hanger clamps but beefier, on the lower half) between each cylinder. Since this comprises the rotating elements of the lower part of the engine (it is rare to find a crankshaft at the top of the engine but it has been done so, like in Nature, there are no single solutions), it is commonly referred to as the "lower end."

On the parts of the crankshaft that are offset from the center of rotation there are bearing journals for the bearings that support the connecting rods, which are connected to the pistons on the other end. Similar kind of bearing. They are fed by pressurized oil from the oil pump and have specifically sized radial gaps for the oil to enter and leave while maintaining a continuous film thickness needed to prevent metal from contacting metal while the parts move relative to one another. The oil is fed to these bearings through passages that are drilled in the crankshaft support bearings and then through the crankshaft out to the connecting rod support bearings. The oil leaves the bearings on the axial ends of each bearing and gets flung around inside the engine crankcase/block area and drains back down to the pan where the pump suction line is located.

2. The rack dampner bolt is the subject of lots of discussion. Do a search to find out all about it. I don't have one on my 240D, so I have not encountered this item.

3. Throttle linkage travel is as leathermang described, how far the throttle moves when you push the throttle pedal from its normal "idle" positon to the floor. There are a couple of places in the linkage where the motion is converted from linear motion to rotational motion. At these joints there is also often a rubber part involved and over time the rubber shrinks and hardens, and the linkages get misaligned. Have someone sit in the car and exercise the throttle pedal while you watch what happens and you will see what I am talking about. The first place where you loose travel is the bushing/bearing bolted to the firewall where the linear motion of the pedal gets converted to rotational motion that goes to a cluster of levers and bars supported off the valve cover, where it is converted back to linear motion. The firewall bushing can just loose a chunk of the rubber and then instead of pure rotation you get some vertical translation before the rotation starts, and loose that much "travel" of the throttle linkage on the injection pump. The cluster of linkage bars supported off the valve cover has a similar propensity to get loose and waste some available travel. Finally, these things can get misaligned with all this unwanted motion and actually bind. This is a common problem on a twenty or more year old car.

4. The thermostat is a regulator like the one on the wall in your house, but it does its regulation by controlling water flow volume and direction by changing the shape of the flow passages in it in response to the temperature of the water that it is in contact with. It is not powered by electricity - it is powered by heat and the differential expansion rates of a set of springs inside it. They wear out after time, and fail to properly regulate the water temperature. When this happens another item in the flow passage of the engine coolant that has a part in it that changes its electrical resistance in response to temperature changes, and is connected on one terminal to the battery and on the other to the temperature gage in the instrument pod, which then sends a specific voltage to the gage where that voltage causes the needle on the gage to take a specific position from the pegged cold spot to the pegged too hot spot. Where the needle sits is dependent on the water temperature, and the condition of the "sensor" or the thing responding to the water temperature. The sensor can fail, as can the mechanism that moves the needle, but the sensor is in a generally harsher environment and is typically more likely to fail.

5. Do another search on engine mounts. When you are in drive and forcing the car to stop with the brakes, the engine speed is dragged down a little, which means the frequencies of the sources of normal vibration excitation for the "system" are reduced. If the car starts jumping around this is a sign the rubber in the engine mounts has aged and hardened, increasing the natural frequency of the mounts. This means the mounts, instead of absorbing the vibrational energy are being excited into a resonant condition, and the vibration level increases even if the level of the input energy is lower. Time for new mounts and there are lots of posts on changing mounts. Not a really difficult thing to do, but it can be really dirty if your car has oil leaks and the like and is oily and dirty. I have learned to wash the engine and the area I will be working on at the do it yourself high pressure spray bays.

6. Yeah, don't sweat those lines between injectors unless they leak.

Now, most of this stuff, except the rack dampner bolt, is pretty straight forward and you should be able to find a "How Things Work" type book at the local library on engines with great illustrations and pictures (crankshafts, bearings, journals, bearing caps, oil passages, the head and its working parts, pistons, and so on). If you do the search you will likely find a post or dozen with photos of the actual old, new and installed rack dampner bolts.

I hope this helps, and good luck with your Diesel, Jim

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Own:
1986 Euro 190E 2.3-16 (291,000 miles),
1998 E300D TurboDiesel, 231,000 miles -purchased with 45,000,
1988 300E 5-speed 252,000 miles,
1983 240D 4-speed, purchased w/136,000, now with 222,000 miles.
2009 ML320CDI Bluetec, 89,000 miles

Owned:
1971 220D (250,000 miles plus, sold to father-in-law),
1975 240D (245,000 miles - died of body rot),
1991 350SD (176,560 miles, weakest Benz I have owned),
1999 C230 Sport (45,400 miles),
1982 240D (321,000 miles, put to sleep)

I fill the engine with coolant by taking the upper radiator hose loose at the radiator end and fill until I see coolant and then quickly put it back and tighten the clamp. Then I fill the overflow tank to the proper level. My experience is, that if you don't do it this way, you will have an "air pocket" and therefore an engine running hotter than it should.

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Diesel-guy

First of all I'd like to say that you should look into that cooling problem because it isn't very good to be over 100*C, it should be a peak of about 95*C. Maybe try a new thermostat, again?

I can't seem to find a picture of the rack damper bolt at the moment but it is located between the IP and oil filter housing near the bottom of the IP. That bolt sticking out of the end of the IP is the rack damper bolt. If it is silverish in color it is the old style, gold is the new style.

I like to keep some extra injector bypass hose around because you never know when they are going to fail. Mine did the day before my order came in with that part. I had diesel everywhere, hood pad was soaked, it even made it onto the windshield. Don't worry about any fuel missing from the hose, they are just a bypass for extra fuel to be sent back to the filter housing.

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Jeff M.
Mercedes W123 DIY pages are now located here.
1983 / 1984 300D Sold
2000 CLK430 Cabriolet ~58k Sold
2005 Avalanche 4x4 ~66k

There are many causes for the high coolant temperature reading. You may want to do some detective work. You can feel the temperature variation of the radiator from top to bottom (with common sense for safety). If there is no flow (blocked radiator, failed thermostat, bad coolant pump, air lock), the bottom will be cold while the top will be hot.

The temp. sensor near the thermostat housing may be suspect too. If the radiator temp does not correlate with over-heating (by feel or more accurate temp. gauge), the sensor is in-accrate.

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Shane83SD

The crank bearings went out on my 115 240 D I now have to roll down a long hill to get it started......
William Rogers.........

William .... will you elaborate on that a little ? How do you know they are out ? How did you have them go out without the rings going out ? Are you using the oil pressure as an indication of this ? Are you talking about the ' crank bearings in the Starter" perhaps ?

I sure hope he means it in the starter because it wouldn't be a very good thing to be driving a car with bad crank bearings. Eventually it'd lead to catastrophic engine failure. Some of the talons get "crank walk" where the crank keeps walking inward due to the crank bearings failing. Normally there are a lot of wierd noises before anything serious happens.

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Jeff M.
Mercedes W123 DIY pages are now located here.
1983 / 1984 300D Sold
2000 CLK430 Cabriolet ~58k Sold
2005 Avalanche 4x4 ~66k

No it came without lectric start I never did trust them lectric start ones anyhow , I mean the crank bearings whar the crank fits in below the grill like on the old Land Rovers my 38 AC tractor would start first pull if you had the magneto set just right............

William Rogers........

William,
I thought it was funny. Some people are just too serious.

These are great replies. Thanks a bundle. And you're absolutely right about the search usually, but this time, I for some weird reason, wasn't turning up enough of a detailed answer to get rid of my confusion. This probably is an indication of my confusion, not others' posts.

Now I have to go away and think about all this.



I've been intending to change the engine mounts...just on principle as a lot of the rubber things seemed nearly shot. And I'll check the radiator tonight.

__________________
Growth for the sake of growth is the ideology of the cancer cell. -- Edward Abbey

1984 300SD: Hilda the veggie vundercar