r129 diesel conversion - PeachParts Mercedes-Benz Forum

bkc · #1 07-24-2014, 01:02 AM

I've been hesitant to post about my project here, as it moves in spurts. But, now that it is moving along more significantly, here we go. Besides, I may need help!

Anyway, quick summary:
=== donor car
1993 300D 2.5L Turbo w124.128 (wrecked by Domino's driver)
OM602.962 turbo diesel 5cyl motor
722.418 tranny

=== project car
1991 300SL-24 r129.061
m104.981 motor
722.500 tranny
instrument cluster was upgraded by previous owner to the newer, digital panel, in case that matters

(The r129 with my lovely and project-supportive wife!)

=== the plan
remove m104, keep 722.500
install om602

=== current status
* I've pulled the motors and trannies, and am working on figuring out all the wiring and such. Two years ago I didn't know what a socket wrench was, so I've learned a lot along the way (am currently semi-apprenticing at a local shop).

* My local shop is scheduled to do the physical alterations for the motor and tranny to fit, sublet the fuel tank reseal, and alter/replace the propeller shaft and exhaust, starting next week sometime.

=== questions so far
* Will the 722.500 tranny work fine with the om602? They have the same bell housing and bolt pattern, so they physically fit. The 722.500 torque converter has a larger pump bore on the tranny side, but otherwise seems identical to the 722.418 (at least from the outside). Can I just plug the vacuum line from the om602 injector pump in where the vacuum line from the m104 went on the .500 tranny?

* How do I get the HGS (TCM) working with om602/EDS output? Is the diesel speed sensor (144/rotation) signal to/from the EDS compatible with what the HGS/TCM wants? What do I use to indicate engine load to the HGS?

* Is the weight/balance going to be fine with the tranny about 4 inches forward of original? (om602 is shorter, but nearly fits existing mount locations by being about the same place from the front as the m104) I know this will require moving the tranny mount stuff.

* Will be modifying the engine mounts crossmember, as the om602 sits too high and doesn't *quite* fit the existing mount points, hopefully won't have to modify too much else physically besides that and the tranny mount.

* Will any particular diesel mesh filter fit the r129 tank? Seems like any of them should?

* I'm planning to have the fuel tank cleaned and "resealed" to deal with the galvanization concerns

* Still trying to identify various wires that don't seem to match the manuals and ETM diagrams (e.g. a thick black-red with white spots wire). I want to make sure I remove/cap unnecessary wires, but not lose ones I need to keep or repurpose.

* The preglow system seems pretty straightforward to integrate into the starter circuit. But, how can I add the vacuum valve to stop the motor? Would prefer a mechanical method, like the w124, so the motor will keep running even if the electrical system fails (saved my butt in the w124 shortly after we originally bought it)

I have the manuals for w124, r129, and w140, plus WIS. I also have access to Mitchell's OnDemand5. My local shop is not expert in Mercedes, more American and Asian cars. They do handle major projects though and have a machine shop for fabrication.

Thanks for any advice or even just moral support!

-bkc (Lynnwood, WA)

OM617YOTA · #2 07-24-2014, 09:18 AM

Awesome project, beautiful wife. Looking forward to hearing/reading how it comes together.

In my (completely different) conversion, I bypassed the stock gasoline filter entirely and used the factory diesel filtering.

I used an EGR vacuum solenoid from the original gas engine to switch vacuum and shut off the engine.

winmutt · #3 07-24-2014, 09:29 AM

Quote:

Originally Posted by bkc

* My local shop is scheduled to do the physical alterations for the motor and tranny to fit, sublet the fuel tank reseal, and alter/replace the propeller shaft and exhaust, starting next week sometime.

Why? You should be able to do this with all stock parts.

Quote:

=== questions so far
* Will the 722.500 tranny work fine with the om602? They have the same bell housing and bolt pattern, so they physically fit. The 722.500 torque converter has a larger pump bore on the tranny side, but otherwise seems identical to the 722.418 (at least from the outside). Can I just plug the vacuum line from the om602 injector pump in where the vacuum line from the m104 went on the .500 tranny?

* How do I get the HGS (TCM) working with om602/EDS output? Is the diesel speed sensor (144/rotation) signal to/from the EDS compatible with what the HGS/TCM wants? What do I use to indicate engine load to the HGS?

Why wouldnt you keep the 602 eng and trans together? You will need to swap EDS over.

Quote:

* Is the weight/balance going to be fine with the tranny about 4 inches forward of original? (om602 is shorter, but nearly fits existing mount locations by being about the same place from the front as the m104) I know this will require moving the tranny mount stuff.

Of course the ratios will be off some but shouldnt matter.

Quote:

* Will be modifying the engine mounts crossmember, as the om602 sits too high and doesn't *quite* fit the existing mount points, hopefully won't have to modify too much else physically besides that and the tranny mount.

Why arent you using m103 mounts?

Quote:

* The preglow system seems pretty straightforward to integrate into the starter circuit. But, how can I add the vacuum valve to stop the motor? Would prefer a mechanical method, like the w124, so the motor will keep running even if the electrical system fails (saved my butt in the w124 shortly after we originally bought it)

Can you not use the 124 ignition?

Quote:

I have the manuals for w124, r129, and w140, plus WIS. I also have access to Mitchell's OnDemand5. My local shop is not expert in Mercedes, more American and Asian cars. They do handle major projects though and have a machine shop for fabrication.

Thanks for any advice or even just moral support!

-bkc (Lynnwood, WA)

This is not the first 129 swap. Google around and find ppl with good experience.

Admiral Ahani · #4 07-24-2014, 11:33 AM

I've always wished they made a diesel R129........

So I could swap in a twin turbo v8 and be smog exempt!

Well, I'm all for it when someone decides not to compromise and they build exactly what they want. Good luck!

Why not make some custom motor mounts (relatively easy) to keep the tranny where it's supposed to be? Seems a lot simpler than driveline modification, and better for handling.

pawoSD · #5 07-24-2014, 11:43 AM

Sweet project. I'd like to do something like that eventually.

mach4 · #6 07-24-2014, 12:33 PM

Nothing better than a diesel sports car!

I like to think of an engine swap as a two step process.

Step 1 is Fitment - This is the process of getting the engine/transmission/driveshaft in the car with the proper clearances and support. If it won't fit, nothing else matters.

Step 2 is Hook Up - Once you know everything fits, it becomes a matter of hooking everything up one system at a time - fuel, exhaust, cooling, control, gauges, climate, electrical, smog, vacuum, etc. and of course the diesel specific stuff - glow, shutdown.

There are quite a number of swap threads that will become a wealth of knowledge to you in thinking through your project.

My own build thread (617->107) - 380SL Diesel Conversion Project

Toyota Pickup - My Official OM617 Toyota Pickup Repower Thread

Studebaker Pickup - 1939 Studebaker coupe express

S-10 - I'm Back! S-10 OM617 Project

606 -> 107 - Not "another" diesel 107!!

These threads probably won't answer your particular questions, but they will provide insight into what is involved and the thinking process used to solve the myriad problems that arise in doing a project.

Please take lots and lots of pictures and document your project for the benefit of others that come after.

Speaking personally, my project would have been an order of magnitude more difficult without the insight, suggestions, ideas and support of this forum.

Good luck.

Oh, and don't forget to ensure that you understand the legal/regulatory issues in your area as it applies to your project so you don't get it done and then not be able to drive it.

Murkybenz · #7 07-24-2014, 03:23 PM

I have posted this before , once today in the wrong thread and a few years back.
Hope it is of help , it shows pics of crossmember alteration and a explains a few other odds and ends.
I am currently searching for the main build up thread and will post a link to it once I find it ( this link is to a thread that is more of an overview of the conversion).
pictures No:petrol out-diesel in - Mercedes-Benz Owners' Forums

Okay this link should open to a two page list of threads started by the builder of the diesel r129 over here in the UK.
http://forums.mercedesclub.org.uk/search.php?searchid=5325686

bkc · #8 07-24-2014, 05:22 PM

Hi, all. Thanks for the responses so far!

Greatly appreciate the advice and support! I've avidly read through mach4's r107 conversion, what I could find of brianbrian's om605/r129 conversion in the UK (seemed to only find the "after" threads, although his crossmember alteration is part of my plan), and whipplem104's om602/w123/722.6 conversion. These threads are what give me ammo to all the naysayers.

mach4: "Speaking personally, my project would have been an order of magnitude more difficult without the insight, suggestions, ideas and support of this forum."

Seeing this is why I finally posted here. It felt like the best "home" for my project!

To answer some of the questions:
> Why not make some custom motor mounts (relatively easy) to keep the tranny where it's supposed to be? Seems a lot simpler than driveline modification, and better for handling.

May have to make custom mounts, but the motor fits almost perfectly being that far forward. All the front stuff lines up (space for oil pan, fan shroud, etc). Moving it back would entail moving the steering linkages I think.

> Oh, and don't forget to ensure that you understand the legal/regulatory issues in your area as it applies to your project so you don't get it done and then not be able to drive it.

Several buddies around here have done other diesel conversions (just not into MBs). Apparently here I just tell them the fuel type changed and that's it, even for emissions testing (one more year of it). Even if I take it elsewhere eventually, a) it is a 1991 so will be grandfathered in most places by then, and b) it is a 1993 motor going into a 1991 car, so fits the newer motor than car requirement many other places.

bkc · #9 07-24-2014, 05:38 PM

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