Engine Shaking---W123 OM617 Turbo---Ideas? What Next? - PeachParts Mercedes-Benz Forum

iladelf · #1 08-09-2017, 04:18 PM

'81 300D w/'84 engine/trans. So, the engine had been shimmying a bit at idle in the engine bay, and would only show itself when slowing down to a stop, at a stop, or shortly after taking off from a stop. My assumption: bad motor mounts. Get the two correct front ones (S11 hardness, Lemforders with Tri-Star logo on them), have a local mechanic install them and...shaking is worse than ever. You can clearly see the engine rocking back and forth in the bay, but even under slight acceleration (in park or in gear) engine seems to right itself.

Mechanic seems to think it is not related to the mounts, but possibly the injectors, because he thinks the car acts like it's "missing". His reasoning is that if a particular injector is fouled or faulty even in the slightest bit, that could be causing said issue.

Me? I'm not so sure he's correct. I think it's possible he may not have gotten the engine/trans lined up properly when bolting everything back down (perhaps). After all, the car is WORSE after the replacement. I also wonder if the transmission mount is bad, causing the issue.

Looking for everyone's thoughts here. Also would welcome recs for someone that's an old Mercedes expert in the West Central Illinois area, or at least someone within a couple hours drive. I think a second opinion would be a great idea at this point.

This is very frustrating, for sure.

Maxbumpo · #2 08-09-2017, 04:44 PM

Injectors or issues in a delivery valve could be the cause. Injectors need to be serviced or replaced about every 100k miles.

t walgamuth · #3 08-09-2017, 05:04 PM

Hello there. Motor mounts are in order if it sounds like someone is hitting the block with a sledge hammer. If its a vibration that goes away with higher rpm it suggests a compression problem....tight valves or a bad ring possibly. To check for an injector problem try cracking loose the injector pipes one at a time and see if it affects the idle. the dead cylinder should not affect the idle the others, yes.

The compression must be good for a smooth idle so a compression test is probably in order soon.

iladelf · #4 08-09-2017, 05:47 PM

Great, so this frickin' diva of a car strikes again! (grr!) After reading online about this possibly having to do with the rack damper bolt, I went outside to do what I thought was a simple "loosen two bolts, adjust the back one inwards until the shaking stops, then lock down the front one". Sure, it's that easy. NO, IT IS NOT. I have stubby wrenches; they get on the bigger front nut, but I have about 1 cm worth of distance between the wrench and the damned oil cooler line, so no way to loosen. And a typical long wrench runs right into something else higher in the bay when attempting to use. There's no room to re-position a wrench either forward on the nut or back: forward runs into the rats' nest of vacuum lines, backwards into all the ALDA and its assorted plastic goodies and linkage. There's no way to get a socket and wrench in there, either; that smacks right into the oil cooler. FML!

Any other suggestions on how to get that frickin' thing loosened? There's gotta be a better way than the stubby wrenches.

iladelf · #5 08-09-2017, 07:30 PM

Through the Internet Wayback Machine, found a website with a pic on the location of the rack damper bolt, and some good info. That said, the pic there has nothing in the way to block the movement of a wrench, so in this case, it looks easy. Mine is like a needle in a haystack. Except the haystack has rigid sections that don't allow you to remove said needle.

https://web.archive.org/web/20060614175744/http://engine.articles.mbz.org/diesel/rackbolt/

Nice to see the original part number on that page, too.

EDIT: After having a difficult time finding said part, it apparently is available here on the Pelican, including the O-ring. There's debate online whether you need the special MB o-ring or if just a standard one that fits will do. YMMV.

http://www.pelicanparts.com/cgi-bin/ksearch/PEL_search_2016.cgi?command=DWsearch&description=fuel+injection+pump+adjustment+bolt

t walgamuth · #6 08-09-2017, 07:56 PM

In owning 30 mercedes diesels I've never touched a rack damper.

chrisgt · #7 08-09-2017, 08:24 PM

I had to adjust mine a couple years ago, didn't remember any trouble getting to it. Just went out to the car now and I can get a 14mm wrench on there no problem. Removing the vacuum line off the side of the VCV helps gain a bit more access, but there's plenty of room to swing a standard length 14mm wrench.

iladelf · #8 08-09-2017, 08:38 PM

I will post a vid link tomorrow showing what I am talking about. Perhaps someone will enlighten me on a different way to approach. I almost enlightened something today; the car itself...with a match.

Diesel911 · #9 08-09-2017, 09:22 PM

I know there is not a lot of room but I did it a couple of times and don't recall any particular issue except that everything was hot because I did it after the Engine was hot.
I likely used the box end of the combination wrenches.

I had previously removed the old Damer Bolt (about 2/3 cup of Oil is going to come out) and replaced it with the newer Gold Damer Bolt and a new O-ring. However, that did not fix the shaking issue and I had to do all the stuff that deals with shaking except the compression test.

When I did it I loosened the large nut and used the end of the Bolt to back it out some so it was having no effect. Then I adjusted the idle speed within the normal idle speed spec.
Then I backed out the large nut more and screwed the Damper Bolt in I beleive it was by hand. Till it removed as much shaking as possible with out raising the idle speed more then a hair.
I held the Bolt stationary with a wrench and used another wrench to turn the larger locking Nut till it was snug.

iladelf · #10 08-10-2017, 02:38 AM

Thanks for being cooler heads than myself, everyone. I just get real discouraged and angry fiddling with this old car. Seems like every two months or less, I'm doing something to it. For sure, these old W123 diesels are not low-maintenance. From fuel filters to valve adjustments to motor mounts to power steering fluid r&r to fixing a/c or heat to automatic door looks to power window operation to steering/suspension issues to exhaust flex pipe replacement to the injection pump to the injectors to...

It...never...ends. Sure, some of this you'd run into with any car, but I have never, ever owned a car that required so much of either my time, my family's time assisting me or in a mechanic's shop.

Back on-topic, I intend on moving some of that rat's nest of vacuum to at least get a wrench on to loosen. Still don't think I'll have enough room to fit the 12mm in to do the adjustment. With a night of sleep, perhaps it will become an easier project to do. For the record, the back of this bolt looks gold, so that to me would indicate the replacement rack damper bolt. Doesn't mean it's still functioning well, though.

t walgamuth · #11 08-10-2017, 06:47 AM

Sounds like you have a car that has not been maintained well. Once you get everything caught up they really are not all that high maintenance. They are 40 years old now though and most cars that age are long gone to the scrap yard.

chrisgt · #12 08-10-2017, 08:00 AM

Pic of 14mm wrench on collar bolt. My car is an 84 and I have no access problems

BillGrissom · #13 08-10-2017, 08:36 AM

No particular problems adjusting the damper bolt. but I have many wrenches to try. Never made much improvement in vibrations.

To verify cylinders are balanced, crack open each injector supply nut while running until it drbbles fuel and verify each has the same effect on making it idle rougher.

chrisgt · #14 08-10-2017, 11:00 AM

My car went from fine to violently shaking all at once when the little spring in the damper bolt broke, so it's definitely worth a try.

SD Blue · #15 08-10-2017, 11:40 AM

As was mentioned before, there are several items to check before messing with the rack dampner bolt. If you adjust it incorrectly, you could end up with hard starting.

Motor mounts, injector line test and especially a valve adjustment.