OM603 Into a First gen 126 - PeachParts Mercedes-Benz Forum

turbobenz · #1 12-31-2012, 03:39 AM

I scored a nice om603 with a #20 head on it from pick n pull. I also got the transmission and really want to put this into my 81 300SD but I'm having a hard time finding information regarding the drive shaft length, motor mount arms and radiator. I am considering going with an electric fan for aesthetics (serp belt without a fan looks nice and clean) and ease of serviceability. I need to get the arms from an SDL so if any forum members have a set I would love to purchase them along with a valve cover.Either the owner, a pnp employee or a customer smashed the valve cover with a hammer right where the timing chain sits in what im guessing was an attempt to convince others the motor was bad. Got it home and took the lower pan off. Motor was clean without any evidence of bearing plating or anything in the oil pickup however I took off the first three bearing caps just to check and they all looked excellent. I threw a bit of delo in each cylinder and cranked the motor by hand quite a bit and did a starting attempt using ATF as fuel. We got it to start fairly easily without glow plugs in a 50F garage so im assuming the compression is decent at this point.

Im also considering sourcing a 5spd manual from a 190e seeing as how the bell housing will accept this transmission. Any thoughts? Anyone know what mpg a car like this could get driving 55mph on the highway?

So yea, I need a valve cover, some mount arms, and perhaps a 300SE driveshaft If I go with the auto. Sixto? I bet you have some valve covers?

pwogaman · #2 12-31-2012, 12:43 PM

The MPG will depend on your differential ratio. As to the drive shaft length, just subtract the difference between a SWB and a LWB from a 300SDL shaft length; also the length should be the same as with the 90-91 350SD. Motor mounts and radiator fitment should be the same as a 300SDL, 350SDL, and 350SD.

vstech · #3 12-31-2012, 06:02 PM

you will DEFINITELY need the radiator from an 86+ SDL!!! DO NOT ATTEMPT TO DRIVE THIS MOTOR WITH THE STOCK 617 RADIATOR!!!
did you keep the oil cooler and lines? if not go get them, there's no space for the 617 oil cooler with the 603 radiator.
cool score!

vstech · #4 12-31-2012, 06:03 PM

OH,... be SURE the valve cover was broken after the fact, not damaged from the vacuum pump failing!!!

turbobenz · #5 01-05-2013, 12:09 AM

The valve cover was not damaged internally. It had been struck from the exterior. Its also free of debris in the pan and ran.You can see marks where he was unsuccessful the first few strikes on the valve cover. Mulling over the driveshaft I realized a 300se will probably have the DS I'm looking for seeing as how the 103 is very similar to the 603. With the radiator...I dont know why the 617 radiator wouldn't work...its not like I'm going to get anything bigger in its place unless they relocated the oil cooler on the sdl's or if the radiator outlet and inlets are in different place. This may be BS but I doubt a 603 produces more heat than a 617. Its the same displacement and a more efficient engine. Anyone else think I'm right on with using a 300SE drivesfhaft? A 350 or late model driveshaft isn't really an option. I think I've only seen a late diesel swb once on the road, let alone at a junkyard.

turbobenz · #6 01-05-2013, 12:14 AM

Oh, I guess it does have a bigger radiator. Where is the sdl oil cooler? I know the w124 has it behind the front bumper in a horrible vulnerable place. Is the w126 the same?

Brian Carlton · #7 01-05-2013, 09:58 AM

Quote:

Originally Posted by turbobenz

Where is the sdl oil cooler? I know the w124 has it behind the front bumper in a horrible vulnerable place. Is the w126 the same?

The W126 is similar. It's behind and slightly below the bumper on the driver's side.

t walgamuth · #8 01-05-2013, 10:10 AM

I have no comments on the practicality of swapping this engine into that chassis, but with a five speed you should be able to get 35 mph highway at 55 to 60...perhaps high thirties....assuming a really sound motor.

Brian Carlton · #9 01-05-2013, 10:24 AM

Quote:

Originally Posted by t walgamuth

but with a five speed you should be able to get 35 mph highway at 55 to 60...perhaps high thirties....assuming a really sound motor.

I agree.

I can get 32mpg with a 617 and an automatic (at 55). It should be very easy to get another 5 mpg from the six cylinder coupled with an OD manual.

65 mph is going to knock it back by 3-4, however.

daw_two · #10 01-05-2013, 10:27 AM

Please post pics of your project once you get under way.

Regarding driveshaft in this swap: You could use the original 300SD driveshaft IF you could put the end of the transmission from the 300SDL in exactly the same spot as the transmission was from the 300SD. I'd definitely measure 4 times before cutting anything and have a gazillion pics and several diagrams drawn. Knowing the transmission and engine combo length measurements would be helpful.

Did you get the motor mount "arms" with the engine? I could see those being helpful.

As mentioned by others, you will definitely want the oil cooler and radiator. Upgrading the AC condensor would be a good idea, too.

ashedd · #11 01-05-2013, 10:44 AM

The 603 in it's stock form uses the larger diameter driveshafts, the same size as the V8's in the w126. So pulling a setup used in a 300se(m103) will not work. You could swap output flanges on the 603's transmission to the smaller stuff, but I'm of the opinion that it's bigger for a reason, likely torque.

GSXR's diff page will help you out, but I don't have the link on this computer.

turbobenz · #12 01-23-2013, 02:08 AM

The problem is finding a second gen short 126 in the junkyard. Theoretically i shouldn't have to fab anything at all which is what I want if I go with a 103 driveshaft and the correct motor mount arms. Its not that I'm too lazy to make my own mounting arms or anything its just that the correct MB solutions do exist. I wouldn't mind the DS diameter-the 300SE puts out nearly the same torque and I can actually find one and get a 40 dollar DS. I will check my EPC and see whether the m103 mounting arms are the same as a 603.

if anyone has a valve cover or mounting arms I would like to buy them. I have good denso compressor from a 420 (YES NO MORE R4 JUNK) and I think i may even have a parallel flow from a 85 123.

Pics will be posted but this may be a few months out.

turbobenz · #13 01-24-2013, 11:44 PM

Ok, I checked EPC and the 603 motor uses the same mounting arms as a m103!

turbobenz · #14 02-11-2013, 03:11 AM

Does anyone know how similar a 87 420 SEL transmission is to a 87 300D one? I need a tailhousing that has the electric pickup for the speedometer. I can get one from a 300SE but I have a bad 420 trans in the shed.

biopete · #15 02-11-2013, 03:22 AM

Will a driveshaft from a W124 87 Wagon work? I'm guessing not or you would have mentioned it. I have that . Also i should have a valve cover and 1 motor mount arm. Not sure which side. I think it is the passenger side. My mount arm actually broke on my 87 wagon. I think i need new motor mounts