Hello from another forum.

[Fulcrum525]

This is my first time posting on Mercedes-Shop. I am an active member at Benzworld and I drop in on MBworld from time to time. Recently I ran into a few problems with my SDL (harmonic balancer and ball bearings in the oil pan.) I found that I could not get an answer from benzworld but after a very long search I found that the diesel specific forum here had all the information that I needed.

A little history- being a that its a 350SDL.....it blew, not by the con-rods bending, thankfully, but by loss of compression in one of the cylinders. When that happened (At 187,000 miles) I decided that it would be prudent to put a different engine in. The donor car was a 1987 300D Turbo that was in a minor accident. thIt was perfect because he head of the engine had been recently rebuilt. I bought the entire car for $800 and on top of the engine we stripped as many parts from it as we could. Its good to know that if my window switch breaks I just have to walk over to the storage bins and pick one out . Everything has been running fine since then with the exception of a bad harmonic balancer install (I should have known better then to let a mechanic touch my car) Because of it I lost two belts last year and the other day the key was sheared in half. Now the balancer is loose on the crankshaft and I have to buy ANOTHER one. Get used to me, I think that I just found my new favorite forum

[techguy512]

Originally Posted by Fulcrum525

....it blew, not by the con-rods bending, thankfully, but by loss of compression in one of the cylinders.

Ummmm, I think that IS the con-rod bending....

[JimmyL]

I won't trash Benzworld as I fly by there from time to time, but you will find far more substantive information on this website, and especially this particular forum. We still get a lot of the Benzworld-ish "modding" threads, but folks just enjoy these cars, and we all have different interests with them.
Welcome aboard, and when you get your balancer situation resolved you will have about the best platform going. Your year W126 with a 3.0 liter would be a great car to have.....
Oh, and your original engine issue does sound consistent with the 3.5 liter....... Matter of fact I think most failures are not of the catastrophic variety, but of the gradual oil consumption increase due to a worn cylinder from a bent rod.

[Fulcrum525]

From what i've read when the rods bend its a quick and catastrophic death. My car just started to shake at idle. We were losing coolent but not oil for the longest time. Here is the original post http://www.benzworld.org/forums/w126-s-se-sec-sel-sd-sdl-class/1212594-dead-350-but-not-con-rod.html

[babymog]

I've not had the failure, but what I've read of it is a more gradual failure as the bent rod ovals the cylinder(s) and starts to consume oil and suffer from low compression. you're already beyond that I see, but if you get bored do a quick search for "rod bender" and you should find volumes. A lot of assumptions. Love the car BTW.

[Fulcrum525]

Originally Posted by JimmyL

I won't trash Benzworld as I fly by there from time to time, but you will find far more substantive information on this website, and especially this particular forum. We still get a lot of the Benzworld-ish "modding" threads, but folks just enjoy these cars, and we all have different interests with them.
Welcome aboard, and when you get your balancer situation resolved you will have about the best platform going. Your year W126 with a 3.0 liter would be a great car to have.....

Yes, the updated interior of the later models is impossible to beat.

[babymog]

I read your Benzworld thread and have a couple of comments:

The 3.0L as installed should give you around 15hp more than the 3.5 had. It is my OPINION that the reason for the lower power and larger engine is an attempt to lower emissions, which made the engine less powerful, so punching it out 16% to try and gain back some of the power and only losing 10% was the response. In addition, the gearing was shorter for better launch, and the 3.5L had better torque down low, but a lower max. RPM. You will probably never get the same launch power the 3.5L had but from 10mph on up it should be faster.

The turbo on your 3.5L was a 55-trim vs the 50-trim on the 3.0, should build more boost sooner. Swap turbos. Keep the 3.0L IP, but adjust the ALDA. Search ALDA here and you'll see what/where it is and how to adjust, most of us have found that 1-1/2turns CCW makes a significant difference in the off-the-line performance. If the ALDA is bad, you can always adjust and install the one on your 3.5L.

The transmissions are similar, but different. The speedo pickup is different of course, and I'm guessing that the transmission is tuned differently: The Torqe Converter for the 3.5L is probably set at a lower stall speed (the RPM where the torque converter tends to stall the engine) to make use of the lower RPM power curve of the 3.5L, to keep the engine RPMs down for better emissions/MPG, and to match the higher ratio (slower) differential by keeping the engine RPMs down. It likely also has lower RPM shift points for the lower RPM 3.5L engine so you don't fully make use of the higher power and higher power curve of the 3.0L. This would be a throttle-body change or maybe just modulators. Could also have different friction material for the higher torque but likely the bearings are the same so it can handle the RPM of the 3.0L engine.

It is a good swap, been discussed and done several times here, I'd consider it myself. I was going to go the opposite way by putting a 3.5L in my 300D until I realized I'd be losing power and speed, ... long story, but I'll be using the turbo and head soon on a 3.0L.

[Fulcrum525]

Yes I noticed instantly that the off the line power of the 3.0 was less however I found that the highway pickup (Where I do most of my driving) is far better. When we did the swap the transmission was slightly different but I still have the 350SDL transmission in the car. And as a backup we still have the trans. from the 300D. The turbo is from the 300D but we still have the (Rebuilt) turbo from the 350SDL, i'm aware of the ALDA and how to do the swap. But it works fine right now so no reason to swap it.....yet

[Hatterasguy]

Did the balancer damage the crank? If so thats a big deal, you have to pull the engine to replace the crank.

[Fulcrum525]

Originally Posted by Hatterasguy

Did the balancer damage the crank? If so thats a big deal, you have to pull the engine to replace the crank.

Thankfully the crank is in perfect condition. What happened is the key sheared in half and it wore out the inside of the harmonic balancer so its loose on the crank.

[Hatterasguy]

Torque the new one on to spec so it doesn't do it again. I forget the specs the FSM would list them but its a lot, like 200ft pounds.

[Fulcrum525]

Originally Posted by Hatterasguy

Torque the new one on to spec so it doesn't do it again. I forget the specs the FSM would list them but its a lot, like 200ft pounds.

I have the shop manuals on cd. Its 320 n/m

[t walgamuth]

Be very careful installing the new HB. Also have your crank looked at to be sure the keyways are not damaged. The keyways are easily damaged of the HB is installed incorrectly. I hope you have not suffered any damage to your crank nose.

Tom W

[Fulcrum525]

Originally Posted by t walgamuth

Be very careful installing the new HB. Also have your crank looked at to be sure the keyways are not damaged. The keyways are easily damaged of the HB is installed incorrectly. I hope you have not suffered any damage to your crank nose.

Tom W

Thankfully the crankshaft is in good shape, ironically its because of the key that we stumbled onto the fact that the vacuum pump had failed. While playing with the key in the keyway we dropped it into the oil pan. We fished it out with a magnet but we also found the ball bearings from the pump in there. We pulled 11 ball bearings out so I think theres still one left. Is this an example of good karma come my way? I'm buying a new pump on Monday and probably a new harmonic balancer as well. When you say install correctly are you talking about torqueing it correctly or is there something else I need to be aware of?

[Hatterasguy]

You got real lucky, those old vacuum pumps have killed more than one 603.