I drove a short distance on the highway at around 70 mph, with a nicely warmed up engine, and when I came to a stop at the bottom of the ramp there was a horrible noise coming out of the engine. It varied with engine speed, becoming somewhat quieter as the engine sped up and a loud banging at idle.

Today I went to look for the source of the problem. The main belt pulley is rattling around loose. This is the thing that comes off the shaft at the bottom front of the engine, and the alternator, fan and power steering are driven off of. The Haynes manual refers to this as the "front balancer assembly" in Fig. 2B.1. I've included a couple pictures with this indicated. I also took a video with my phone, but it's 90 megabytes and I can't upload that to the gallery (and the other place where I sometimes upload files to share has a 20 MB limit). If it's helpful I'll try to figure out how to cut it to a 20 MB segment so you can see exactly what it's doing.

But basically the entire thing is rattling around, so that the pulleys move not just up and down, but their axis is moving as well (so that they're no longer perfectly perpendicular to the shaft in the engine).

I'm hoping this could be a relatively minor exterior repair but the amount of noise has me worried something important has broken inside the engine. OTOH, the engine starts normally, produces the normal amount of power, and I didn't see any metal shavings on the dipstick or on the valve train bits visible through the oil fill cap.

What would this most likely be? Anyone had this happen to them?

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1982 240D automatic
Odometer quit at 307K...about 325K now

Put your keys in the mail to me and I promise I won't send them back until you fix the damper. Until the experts chime in, I think you're 6 bolts and a new damper from fixing what's wrong. If it comes apart, you're a radiator, fan and maybe a crankshaft from getting back on the road.

Sixto
83 300SD

Don't drive it or run the engine for now.
Same thing happened to my 78 300SD.

The main pulley wobbled bad enough to hit the water pump pulley and damage the water pump shaft.
I thought my crankshaft had sheared.
The 27 mm bolt holding the crankshaft pulley to the crankshaft nose had loosened and backed out.

My independent mechanic did the repairs, which involved replacing the main crank bolt and 3 cup washers crank pulley assembly with a good used one, new water pump and my smaller diameter water pump pulley from an 85 300SD with new 1025 mm Continental belts.

The belts squeal as they are a little too long. I have a pair shorter 1005 mm Continental belts that I need to install.

Fortunately, the nose of the crankshaft was okay. Hopefully, your crankshaft is okay as well.

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78 W116 300SD 'Desert Rose' new as of 01/26/2014
79 W116 300SD 'Stormcloud' RIP 04/11/2022

Ditto Six & Alec. It's the crank pulley & dampener assembly. Check the bolts, they're most likely loose/missing. With luck the threads are OK. Buy new dampener & bolts, clean the threads, apply loctite & torque to spec. Install new belts, tighten, run engine a few minutes (maybe 30), check and tighten belts as needed. After a day or so, check the bolts again.

OK, thanks guys. This makes me hopeful. I have a call in to the mechanic.

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1982 240D automatic
Odometer quit at 307K...about 325K now

As long as the mechanic comes to the engine, or you tow it there, fine...

Do not start the motor until this is fixed!

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John HAUL AWAY, OR CRUSHED CARS!!! HELP ME keep the cars out of the crusher! A/C Thread
"as I ride with my a/c on... I have fond memories of sweaty oily saturdays and spewing R12 into the air. THANKS for all you do!

My drivers:
1987 190D 2.5Turbo
1987 560SL convertible
1987 190D 2.5-5SPEED!!!

1987 300TD
2005 Dodge Sprinter 2500 158"WB
1994GMC 2500 6.5Turbo truck... I had to put the ladder somewhere!

X5

Plus....check each of those bolt holes individually with a new bolt...before you start to put it back together..... ANY resistance or failure to find smooth threads... get a thread chaser tap of the proper size and thread.... start those by finger only...
Then really clean out those holes with spray brake cleaner or something like that ... electronic cleaner... something which will not leave an oily film.. not WD40 for instance... nothing which could interfere with the aforementioned Locktite properly setting. When starting to put it all back together put one drop into the hole and one drop on the bolt shaft... if you only put it on the bolt it may be wiped off as you install.

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1980 240d ,

chain elongation, cam marks reference:
http://www.peachparts.com/shopforum/diesel-discussion/10414-help-i-need-check-stretch.html

http://www.peachparts.com/shopforum/diesel-discussion/305365-9-degrees-chain-stretch.html

evap fin cleaning:

http://www.peachparts.com/shopforum/diesel-discussion/156207-photo-step-step-post-showing-w123-evaporator-removal-1983-240d-1982-300td.html?highlight=evaporator

A/C thread

http://www.peachparts.com/shopforum/diesel-discussion/297462-c-recommendations-mb-vehicles.html

I will try to get the mechanic to be thorough about this. I don't want to offend him by telling him how to do his job, but I can pass this stuff on, since it was addressed to me.

And I will definitely not be starting the car until it's fixed.

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1982 240D automatic
Odometer quit at 307K...about 325K now

Well, I finally got the car back from the mechanic. A couple more questions:

1. Apparently the bolts flying off caused a small hole in the radiator. I have not seen it yet, but it must be fairly small since I never noticed it. They wanted to replace the radiator, but quoted me $880 (including a new radiator and hoses) and I have trouble with that right now, having paid $1,000 for them to replace the crankshaft pulley and change the brake fluid. I know there are epoxy-type products suitable for a case like that (a small hole caused by mechanical damage). Any recommendations for what to use?

2. The fan shroud is kind of torn up. It wasn't when I brought it in, they must have had trouble getting it off. How important is that? I haven't even looked to see how hard they are to find (he quoted $33 for a new one). Are these easy to get off and on?

Thanks!

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1982 240D automatic
Odometer quit at 307K...about 325K now

$880 for a 240D radiator + replacement is pardon my language ****ing insane. that's a job you could do at home that will take an hour and they still make 240D radiators so pick what you want, a cheap one for $80 or a brand new behr for $200

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1981 NA 300D 310k miles

They are probably quoting him for a new MB one

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Chris
84 280sl
82 300d euro

Yeah, that did seem steep to me.
They quoted $575 for the radiator, and I do see I can get a Behr for $199.

My problem is that my time is so scarce with two little kids that I'm afraid to take jobs on. I'll get interrupted and never know when I can get back to it.

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1982 240D automatic
Odometer quit at 307K...about 325K now

Ask them if you can supply parts. On the other hand I have repaired a damaged radiator cores with little effort and no problems after. This was years ago.

Depends on what you see. I even closed off one or two cores totally in the process if the need was there. If you are unwilling or unable to do your own repairs on an older car. You need a cheaper alternative to work on them. Ask around.

Many people stay in pretty new cars because all too often almost any repair paid for is pretty hefty today.

I have many young guys call me asking if I know where there is an older cheap car. There are tons of them but if they state they cannot repair anything at all themselves when asked. Or know a good backyard mechanic. It may be cheaper overall to buy a stripped down new car today.