The M130 Engine Conversion is a doable conversion for the 404 Unimog. However, it is not a "plug and play" conversion. Also, keep in mind you are increasing your HP from 90 to 115. While a significant HP increase, it comes with some expense and effort.
The Below emails were from a thread from 2001 when we had just completed a conversion. In addition John Wessels, filled in some gaps.
From: Scott Ingham [mailto:firstname.lastname@example.org]
Sent: Friday, March 23, 2001 8:01 PM
Subject: 2.8 Conversion Check-list
The 2.5 and 2.8 MBZ motors make very good candidates for an engine
conversion in the 404. However, it is not a simple "bolt-in" swap. The
following is what I recently did for a 2.8 conversion, in "layman’s terms."
Engine Block - I started with one out of a 1974 sedan. I prefer the newer
M130 motors because they have better cooling characteristics. Each year MBZ did cooling modifications to the casting, the goal is to get one that has all of the modifications.
Machining - Whatever is required/preferred. Machine Shop bill usually runs $3000-$4500 depending upon what is done to the block and head. New Pistons run $150 a piece, etc. etc.
Flywheel - It is preferable to get one of the "thick flange" flywheels to work with. The holes in the flywheel for the stretch bolts will need to be drilled out to 12MM. The flywheel itself will need to be balanced. I prefer to balance the flywheel along with the crank.(A Huge amount of material will need to be removed on the opposite side of the "half-moon" on the flywheel. The half moon was designed to balance the 2.2 crank.)
Oil Pump - the pressure relief valve on the 2.8 pump does not clear the front of the Unimog Oil Pan. (The Unimog oil pan must be used in order to maintain the rigidity with the long bell housing.) You can remove the pressure relief, cap the hole, and screw it into the front oil galley. The engine works great with one pressure relief.
Oil Pan Mod - The stock 2.2 pan does not clear the rod bolts. You must grind the pan until the bolts clear. There is a lot of material on the pan, I usually have to take off 1/16-1/8th of an inch.
Alignment Dowels - (These are the dowels that align the engine to the bell housing.) The 2.8 alignment dowels are much larger in diameter than the 2.2 dowels. Have the machine shop remove the 2.8 dowels and order the proper ones from your dealer.
Front engine mount, pulleys, fan, water pump, fuel pump, distributor, oil filter housing, tensioner, generator, starter, can all be used from the 2.2 motor.
Use whatever manifold/exhaust that suits you. I prefer the manifold/exhaust from the car 2.8. We welded the stud holes up in the aluminum, machined it smooth and re-drilled and tapped for 2 stock Unimog carbs. Fabricate your own throttle linkage so both carbs open at the same rate.
I definitely like the power of the 2.8. It is advised to use the "tropical" radiator and water pump pulley to help with the cooling.
The next time that you are told that the 2.8 is a drop in conversion, well they are somewhat correct.
Expedition Imports, Inc.
From: john wessels [mailto:email@example.com]
Sent: Friday, March 23, 2001 9:30 PM
Subject: Re: 2.8 Conversion Check-list
Need to add a little to that list.
Engine oil cooler If the sedans had one installed what makes people think that the oil temp will be lower in a 404?
Also helps to install a thicker fan spacer so that the cooling fan runs closer to the radiator and pulls more air through.
Need to plug off the heater hose pipe at the rear of the cylinder head.
Exhaust downpipes must be fabricated. The 404 pipe will not bolt up to the M130 exhaust manifolds. Will then need to clearance the cab/inner fender well to clear the new downpipe.
Need to buy one more Mog carb.
Need to install the missing pilot bearing. As most car engines are automatics and don't have one.
Will need a new set of plug wires so that sedan plugs can be used. Yes, the military style plugs will run, but not very well.
Air cleaner ducting needs to be modified to fit the dual carbs if you still want to use the original oil bath. Not much room on the rear carb to fit an air filter on top.
Must be very careful building linkage for the dual carbs. If not, you can have one opening at a very different rate than the other.
Will need new flywheel stretch bolts.
Will need new connecting rod stretch bolts.
As stated before the machining costs and parts list can get very expensive in a hurry when rebuilding the M130 engine. I would never consider buying a salvage yard engine and bolting it in a 404 without a complete rebuild. An engine that has already used up more than 3/4's of it's life and asked to turn over 4500 constant RPM isn't going to last very long.
If your transmission is hard to shift and runs hot the added power from the M130 will shorten it's life considerably. If your tranny doesn't have recent rebuild tags on it plan on replacing that too.
It seems the list never ends when doing this conversion.