A Turbodiesel Conversion for the Unimog-S:

Engine and Chassis Preparation

CLICK this text for more PHOTOS and INFO - This takes you to the advertisement for the recent sale of this Unimog. It has been SOLD but the page remains if you're interested in seeing more photos of the Unimog.

(click the photo above for a larger version and .wav file)

This page has had some photos thumbnailed, so please click any to enlarge.

I bought an Unimog 404 VLF in 1997. I like to explore the dirt back-roads of Wyoming – we have over 8000 miles of them – and was very interested in the prospect of using an Unimog for remote camping trips. The picture above shows the truck as it sat in Germany after the broker located and prepared it for me. (Credit to Dirk Rautenburg for the photo) Yes, that's a radio box, not the VLF box, but it was okay with me! More camping room! The truck came in with a blown M180 engine. I took delivery of the truck "as-is" and since I'd paid for a good-running truck, the seller returned some money.

Now I had the job of deciding what to do with the blown engine. Would I repair it? Replace it with a factory rebuild? Maybe an M130 2.8L with twin carbs! I decided that would give me the power I needed, since I lived at 5,500' and the M180 was terribly gutless at that elevation.

To make a long, long story short, I dinked around with a couple of M130s and before making a final plan, had the opportunity to drive Rob Pickering's  turbo-diesel double-cab 404. After one drive, the M130 plan was scrapped and I was looking for an OM617A turbo-diesel engine. A friend found me two very nice low mileage 617A engines. One was a 617.951, the other a 617.952. I chose to use the 617.952 as it was very clean inside and had all German filters on it. It appeared that someone had taken exceptional care of the car that this was from. Too bad for them that the car got totaled.

Here is a picture of the engine...

According to the salvage yard, this engine had come from a Euro 300D Turbo, but I've seen conflicting info regarding this. The picture above shows how it was delivered to me. The only difference is the new flywheel which has been temporarily bolted to the crankshaft. More on flywheel balance and parts required later.

The next step was to prepare the chassis. I removed the box and cab, then removed the blown M180. Here's a shot of the chassis, ready to go into the shop...

While the chassis preparations were taking place, I was also placing an order with Mr. Gerald Dietrich in Germany. Gerald is the gentleman who replied to my email after surfing around on the "Dieselization" website. Click here to visit the English version of the German Dieselization site. I ordered the following items to facilitate the conversion:

There were other things I could have ordered from him, but chose to fabricate or source them locally. I did NOT buy the diagonal ties (to tie the bellhousing to the engine block) nor did I buy the "Clutch Fork Lengthening." I'll discuss the function, fabrication, and importance of these items later. The parts from Gerald arrived about a week after wiring him the funds. They were well crated and in perfect condition. I immediately opened the box and was very impressed with the quality of parts.

Here you can see the Strong Steel Flange and Clutch Housing...

Now that the parts were here, I could have the new flywheel unbalanced as the original that came with the motor. Chances are that a used motor found in United States would have been mated to an automatic transmission, and my engines were no exception. The automatic transmission flywheel, or flexplate as it is sometimes called, is NOT zero balanced. The flange of the crankshaft has twelve holes and you can install the flywheel in twelve different positions. ELEVEN ARE WRONG!!! There are NO locating pins or offset holes.

The following steps should be followed to insure a good balance for your engine:

1. Set the engine to TDC.
2. Using a prick-punch or scriber, mark the crank flange and flexplate at the twelve O'clock position.
3. Remove the flywheel.
4. Remove the aluminum spacer used with the automatic transmission. It's not going to be stong enough for the Unimog application. It will be replaced with the Strong Steel Flange.
5. Deliver this flexplate and your new flywheel to a reputable balance shop. I used a place called Equipoise Balancing Lab in Longmont, CO. Explain your situation and explain the mark on the flywheel.
6. The balance lab will basically zero-balance the original flexplate, then record the weights used for balance. These weights will be transferred to your new flywheel in the opposite position, or that amount of weight will be removed from the flywheel at the same position. The new flywheel will also now carry a mark representing the twelve-O'clock position when the engine is at TDC.
7. Install the Strong Steel Flange.
8. Check that the engine is still at TDC.
9. Install the new, now unbalanced flywheel.

This procedure should result in a perfectly balanced rotating assembly. If the flexplate was removed from the crankshaft without indexing marks, you will have a hard time getting the proper balance.

At this point, before installing the entire clutch assembly, I bolted the empty bell housing to the engine via the Strong Steel Flange. Here is the engine, stripped down, with the strong steel flange attached...

The engine's vacuum pump has been removed for space considerations, and the hole has been covered with a plate available from Mercedes for about $35. If you need vacuum, there IS room for the pump, but I need the space for something else. ;-) Sorry, I can't find the part number at the moment...

The bellhousing has been bolted to the transmission and you can see the angle at which your new engine will sit... This angle helps the injection pump clear the driver's floor and engine cover...

Here's the engine installed for the first time...

The engine will have to be removed for welding in the front engine mount bracket in the next step. Due to this, I installed it sans clutch, to make assembly to the transmission very easy. Now that the drivetrain is together, the front engine mount (Engine Bearer) can be assembled to the front of the engine and the bracket to which it bolts can be welded to the front crossmember. The photos below show the process I went through to locate and afix the bracket.

Here, I have bolted the mount together and raised the engine until the yellow bracket is in contact with the front crossmember. Once the alignment of the holes underneath has been checked, it can be tacked in place...

Here is the view from underneath. You can see the bolt which functions as the pivot for the front of the engine, thus allowing the frame to flex around it without stressing the assembly. Traditional Unimog style!

The engine must now be removed so that the yellow bracket can be welded properly. After preparing the metal for welding, I stitched the yellow bracket to the crossmember...

This yellow bracket has four small pilot holes drilled in it. There are four corresponding holes in the actual engine mount. These holes must be drilled into the crossmember, then tapped for an M14 bolt...

With the mount finished, the clutch can be assembled and the engine installed again and bolted down to its new home. To ease the assembly, I used my lathe and fabricated a clutch alignment tool from aluminum. Below are pictures of it after construction and during use...

Note the pilot bearing, made up of the actual bearing and a cover ring. They are part numbers 115 980 01 15 and 189 031 00 33 respectively....

The engine and clutch slipped right onto the input shaft and bell housing and I bolted the front mount down. Before anything else, I wanted to make some diagonal braces to beef up the engine/bell housing connection. They are crucial in this application, as the engine/transmission is supported at the rear of the transmission and front of the engine. This design allows maximum frame flex, but severely stresses the bell housing to engine bolts, as they are only threaded into aluminum in many locations. Mercedes-Benz thought it was important enough to design these braces into the M180-powered Unimogs, so I decided I should have them too!

When you build them, make sure there won't be any interference if you hit a good bump and compress the front suspension. My first left-hand brace did contact the axle and ding the vent tube.

Gerald Dietrich sells them, but I chose to build my own, saving some weight in the crate that was shipped to me. Here are my braces... They bolt to the sedan engine mount locations, and run to the bottom of the bellhousing...

I also needed to build myself the other thing I chose not to buy from Gerald... The "Clutch Fork Lengthening." This lengthens the clutch fork arm on the outside of the bellhousing, reducing forward travel of the throwout bearing and reducing pedal effort in the process. This modification is necessary to prevent the throwout bearing from contacting the rotating input shaft. Here's my system...

I now wanted to focus on my two crucial accessories, the alternator (24VDC 40 Amp) and air compressor. I fabricated some simple brackets and welded them to the passenger side engine mount. Once installed, I found a belt that fit and bolted the alternator in...

Air-assisted brakes need an air compressor. I was pleasantly surprised to note that the original position of the compressor was fairly close to the 617A front crankshaft pulley. It was not perfect, however, and there were no pulleys small enough to prevent compressor over speed at engine redline. I needed something on the front of the pulley assembly, of a smaller diameter. I used my lathe to turn a pulley that would insert into the front of the original equipment 617A pulley and bolt in, allowing removal for future balancer bolt access.

The insert (left) and the insert installed into the 617A crank pulley set (right...)

Here's the final compressor mounting... It bolts down in the original position... You MUST BE SURE that the pulley ratio will not allow the compressor to spin over its MAX speed, which I believe to be 2100 RPM....

I also modified my oil pan by relocating the drain plug to the new "low spot." I simply drilled a hole in the tin pan, TIG welded a nut to the bottom of the hole, and screwed a magnetic drain plug into the hole...

Thanks for sticking with me so far. You can EMAIL ME about this swap if you like. Click below to move on to...

Cab Installation and Modification

OR

Return to our Home Page     Back to Unimogs