Creating Manifold / Fuel Rail

 

 

In today's episode, we finally get down to the business of retrofitting modern fuel injection into a 1971 Mercedes 250. But first a quick history lesson.

The M180 line of engines was first introduce in the 1950s on the Unimog (a German troop carrier). The Unimog flavor was fed by a single carburetor. Mercedes updated this engine several times and used it in cars as late as the w123 chassis in the1980s, this (M129) was also fed by single carb. Apparently a troublesome one at that. 

So how did we decide this old dog engine was worth saving? Well, for one straight sixes of that era have earned a reputation for being bullet proof (see small and large block Fords), considering it ran in various forms for over 30 years, also it was commonly used in E and S class vehicles in the late 60s and early 70s. 

For instance, my W114 250 like all the stroke 8s, are considered predecessor to the E-Class, came with an M130 (another iteration of the M180), and dual Zenith-INAT 35/40 carbs. In my case I got a deal on this machine because everyone though the engine was smoked (it wasn't the timing was ~20 degrees off) as were the carbs (see engine timing, the carbs were OK- but the accelerator pumps were just hanging on by a thread). So at $2k to rebuild carbs or $3-4k for major upgrade I could blog about and well, here we are.  

Back to the history lesson. In the sportier models of the late 60s / early 70s. One option was mechanical fuel injection, specifically Bosch D- Jetronic. This was available in W109/W113 S-Class and according to rumor in Europe there was a 250CE (W114) that also had it. I've also read the Gemans even took a first crack at computer controlled injection around this time though the computer was analog not digital. 

Oh those crazy Germans- well intake manifolds are readily available on e-bay if you have a machine shop, and if you don't, contact us and we can do one for you. 

Spoiler- this is what it will look like.

Milling Rail Stock and Manifold

Unfortunately, the manifold was milled before we had the idea to do this blog, so there are no pictures,  it was just 6 holes drilled along the old fuel rail (which was cast into the manifold). The holes were just large enough for injector bungs, but next time we'd probably mill the holes just big enough for the injectors (as we did on the rail).

 

As always when milling we start with some nice pilot holes, and slowly work our way up to an end milll. And since we're working on aluminum, we're going extra slow.

And our work pays off.

We forgot to take a picture with the injectors in both the manifold and the rail, but they do fit- here's another important tip- you can eyeball the whole thing since the injectors have O-rings and some natural tolerance to how they sit.

  

Wes was really insistent about  putty welding the bungs in- this putty weld is not structural- there will be slight downward pressure on the bungs which rest on a little lip in the holes w drilled in the manifold. All this putty weld is doing is preventing air leaks from developing over time.

 

 Shape of Things to Come

I like to plug things in to give me a sense of hope- in this case, I timed out on my project and was recalled early from vacation. But we're pretty close as the pictures show. The last bits are:

 

 

We still need to create a block off plate on the manifold for where the cold start valve used to be (that hole towards the bottom of the picture above).

Second we need to figure how to run a throttle cable, and from where, to where it will run. After that a (fuel only) setup on the Megasquirt will be an easy add.