New engine mount, now the engine is rocking - in a bad way - PeachParts Mercedes-Benz Forum

eatont9999 · #1 10-03-2013, 11:08 PM

I am uploading a video to youtube and I will post it ASAP.

I purchased my new 300SD with a known bad motor mount on the driver's side. The PO said the primer pump failed and leaked on the mount. He replaced the hand primer with a new unit but left the mount in shambles. The car was uncomfortable to drive in its condition, so I replaced the driver's side motor mount and transmission mount yesterday. I was expecting a smooth as silk idle like my grey 300SD after replacing the mounts. It seems like I have another problem that has revealed itself.

The rocking of the engine occurs at idle hot or cold. If I bring the engine off idle, it smooths right out. I am still working through some troubleshooting but I have limited time given my day job. I have done the following so far:

Diesel purge - has turned the fuel black; even what is in the tank
Valve adjustment - almost all valves were too tight
Italian tune up - I put half a bottle of Diesel Kleen in 1/2 tank of fuel, put it in second and floored it for a few miles.
Replaced primary and secondary fuel filters.
Re-sealed fuel filter housing.

I know I have a lot of things to try and hopefully I will have some more time this weekend. The PO did run SVO and it is unknown what he actually put in the car. The car has plenty of power and runs like a champ on the roads. At this point, I do not believe it is fuel starvation. I can get up to 80 MPH without a problem.

I hope to test the injectors and compression this weekend. Any suggestions are appreciated. Someone might come up with something I overlooked.

eatont9999 · #2 10-03-2013, 11:09 PM

1983 300SD engine rocking after new motor mount - YouTube

Danman · #3 10-03-2013, 11:19 PM

New rack damper solved my engine rocking despite its good motor mounts.

Zacharias · #4 10-03-2013, 11:32 PM

Okay, for starters that is not serious rocking. Seriously. I have driven a DD for months that was waaaay worse. That is not unusual, but not 'normal'.

The motor sounds excellent so I don't suspect any injector or fuel delivery issues.

Setting up a smooth idle is a two-fold process, involving the rack damper bolt and the idle adjustment screw. As these cars age they each tend to have their own 'ideal' idle speed (at least in my experience).

The rack damper bolt compensates for end float of the camshaft inside the injection pump. It is only found on turbodiesels. There is an upgraded bolt, gold in colour, that many cars need to achieve a smooth idle.

Edit: see this thread: http://www.peachparts.com/shopforum/diesel-discussion/343878-idle-problem.html

eatont9999 · #5 10-03-2013, 11:36 PM

Quote:

Originally Posted by Danman

New rack damper solved my engine rocking despite its good motor mounts.

Did it rock as badly as the video shows? If so, I will try the rack dampener bolt that I took out of my first 300SD. It never rocked or vibrated this badly.

eatont9999 · #6 10-03-2013, 11:41 PM

Quote:

Originally Posted by Zacharias

Okay, for starters that is not serious rocking. Seriously. I have driven a DD for months that was waaaay worse. That is not unusual, but not 'normal'.

The motor sounds excellent so I don't suspect any injector or fuel delivery issues.

Setting up a smooth idle is a two-fold process, involving the rack damper bolt and the idle adjustment screw. As these cars age they each tend to have their own 'ideal' idle speed (at least in my experience).

The rack damper bolt compensates for end float of the camshaft inside the injection pump. It is only found on turbodiesels. There is an upgraded bolt, gold in colour, that many cars need to achieve a smooth idle.

Edit: see this thread: http://www.peachparts.com/shopforum/diesel-discussion/343878-idle-problem.html

The first car is the one in question before the motor mounts or any other mentioned maintenance was performed. The second car has all maintenance performed as well as a new, upgraded, rack dampener bolt. I remember on the second car shown, the motor mounts were the last things I did, so they made the most difference.

300SD motor mount difference - YouTube

Danman · #7 10-03-2013, 11:44 PM

Quote:

Originally Posted by eatont9999

Did it rock as badly as the video shows? If so, I will try the rack dampener bolt that I took out of my first 300SD. It never rocked or vibrated this badly.

Mine rocked at least as much as yours. Sitting at idle it was enough to rock me back and forth in the seat. I put the new gold one in and adjusted nearly all of the vibration out. I still feel a slight motion in the drivers seat but nothing like before.

Zacharias · #8 10-03-2013, 11:46 PM

Idle problems can have a number of sources. Yes some people report huge improvements from new motor mounts. Likewise injectors. Likewise rack damper bolt.

Personally I have seen motor mounts completely gone to the point where the entire car was throbbing and reverberating from the motor at idle, but the idle was smooth (as in no rocking).

Each situation is different and people will tend to answer with what has worked in their experience....

eatont9999 · #9 10-03-2013, 11:50 PM

Quote:

Originally Posted by Zacharias

Okay, for starters that is not serious rocking. Seriously. I have driven a DD for months that was waaaay worse. That is not unusual, but not 'normal'.

The motor sounds excellent so I don't suspect any injector or fuel delivery issues.

Setting up a smooth idle is a two-fold process, involving the rack damper bolt and the idle adjustment screw. As these cars age they each tend to have their own 'ideal' idle speed (at least in my experience).

The rack damper bolt compensates for end float of the camshaft inside the injection pump. It is only found on turbodiesels. There is an upgraded bolt, gold in colour, that many cars need to achieve a smooth idle.

Edit: see this thread: http://www.peachparts.com/shopforum/diesel-discussion/343878-idle-problem.html

That thread sounds about on par with what I am experiencing. Sans anything to do with being in gear or not. It actually rocks more when in neutral or park. Tomorrow, I will try to locate my old rack dampener bolt and or try adjusting the one in the car. The injectors are not the problem. I know enough about them that I can confidently say they are fine; so is compression. There simply are not enough symptoms related to the two for the problem to be in those areas. This car rarely smokes; ever and there is no thumping sound like I would expect from bad compression.

Diesel911 · #10 10-03-2013, 11:54 PM

Quote:

Originally Posted by Zacharias

Okay, for starters that is not serious rocking. Seriously. I have driven a DD for months that was waaaay worse. That is not unusual, but not 'normal'.

The motor sounds excellent so I don't suspect any injector or fuel delivery issues.

Setting up a smooth idle is a two-fold process, involving the rack damper bolt and the idle adjustment screw. As these cars age they each tend to have their own 'ideal' idle speed (at least in my experience).

The rack damper bolt compensates for end float of the camshaft inside the injection pump. It is only found on turbodiesels. There is an upgraded bolt, gold in colour, that many cars need to achieve a smooth idle.

Edit: see this thread: http://www.peachparts.com/shopforum/diesel-discussion/343878-idle-problem.html

I think you mean the Rack.

Diesel911 · #11 10-03-2013, 11:56 PM

Long Fuel Pressure Relief Valve/Overflow Valve Thread
Fuel pressure relief valve adjustment - PeachParts Mercedes ShopForum

cooljjay · #12 10-04-2013, 12:15 AM

My car idles with a rock to probably not as bad as yours but it rocks.....nice smooth idle just rocks.....hoping a trans mount and new relief valve if I can ever find one.....may help and possible re timing the injection pump.....but I am not holding out hope...if it happens it happens....

I have the same thing wrong with my valves they were as tight as can be....I have done numerous adjustments and every time they are still tight....I imagine once I get them to hold the gap, then my idle will smooth out....as it is....there is a lot of built up carbon on the valves that needs to be banged off...this may be your issue as well...

Despite what people say, burning organic material aka wvo in a car will produce a lot more carbon....

eatont9999 · #13 10-04-2013, 06:23 PM

I will start with the rack damper bolt. What happens if I remove the lock nut (temporarily for testing) in order to turn the bolt in further? Since the upgraded bolt is longer, I want to prove that a new bolt will solve the problem before dumping another $75 into the car.

Would pinching the return line have the same effect as increasing the pressure in the IP? Could that be a quick and dirty proof of concept for a fuel relief issue?

eatont9999 · #14 10-04-2013, 06:27 PM

Quote:

Originally Posted by cooljjay

I have the same thing wrong with my valves they were as tight as can be....I have done numerous adjustments and every time they are still tight....I imagine once I get them to hold the gap, then my idle will smooth out....as it is....there is a lot of built up carbon on the valves that needs to be banged off...this may be your issue as well...

Despite what people say, burning organic material aka wvo in a car will produce a lot more carbon....

When you do a valve adjustment, can you rotate the valve some to knock the carbon off? It may help. I have heard of it being done in the past.

barry12345 · #15 10-04-2013, 08:27 PM

Quote:

Originally Posted by eatont9999

I will start with the rack damper bolt. What happens if I remove the lock nut (temporarily for testing) in order to turn the bolt in further? Since the upgraded bolt is longer, I want to prove that a new bolt will solve the problem before dumping another $75 into the car.

Would pinching the return line have the same effect as increasing the pressure in the IP? Could that be a quick and dirty proof of concept for a fuel relief issue?

Only if lift pump pressure output is relatively normal.