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Putting a M116 into 280S

Started by Nabstud, 23 September 2023, 09:53 AM

Nabstud

I'm looking at putting a M116 into my 280S but I want to put a carb on it to keep it simple.
Anyone done this? Anyone know of someone that makes an inlet manifold to suit? I know it's not a common conversion but hoping I won't have to reinvent the wheel...
Seen someone make their own manifold on youtube but my fabrication skills don't go that far.

I've managed to pick up a complete 350SEL for parts so I have all the mounts, radiator etc.
1975 280S - Australian delivered

daantjie

Anything is possible with enough time and money 8)
Daniel
1977 450 SEL 6.9 - Astralsilber

ramiro

Does the 350sel run and has K jetronic? If yes you could keep the injection system you just need to wire the fuel pump relay and add the fuel pump set, for wiring the engine harness only needs a wire from to fuel pump relay output to the warmup regulator and a starter signal for the cold start valve , i would say that it should be much easier then modifying the intake manifold.

Mechanical putting the engine in should same as putting a 280 back in , there is nothing special you just have to change the exhaust and the driveshaft.

Nabstud

Cheers. It's a 1975 350SEL with Djet so I think I'm out of luck going that route.
1975 280S - Australian delivered

ramiro

Personally i would transfer the d jetronic system but if you are afraid of wires that would be a bad job , the engine harnes on d jetronic cars is seperate so you could remove it with ecu and add it to the 280s , the problem is that some wires go to the fuse box because there are 3 relays for the injection (pump , main power , cold start valve) .

Offcourse if the 350sel is not running it would be even harder.
Actually with the d jetronic manifold you could quite easily also use a aftermarket ecu but then you must know how to tune your engine.

Nabstud

It currently only runs when fuel is put straight into the inlet manifold. It did run for about a minute on its own, not 100% if that was just on the fuel I poured in or the D-jet was doing something. Fuel pump primes for a second each time the ignition is turned on which is a bonus! Been sitting for almost 10 years so fuel system probably needs a full going over.
1975 280S - Australian delivered

ramiro

Ok , then you have to decide for yourself if you want to fight with d jetronic if you have some basic eletronic knowledge it could be easier and cheaper then getting a k jetronic running.
I have reactivated serveral k and d jetronic cars that sat for long and usually k jetronic needs a fuel distributor and warmup regulator overhaul and D jetronic needed some taps on the injectors and some pulses with 12v to get them unstuck and the car ran.

Nabstud

I had a bit of a play with it. New cheapy fuel filter, replaced a few fuel lines and it runs! Well it idles and revs well considering it has sat for many years.
1975 280S - Australian delivered

ramiro

Then you could transplant the engine harness with ecu and fuel pump assembly and use the d jetronic i think it would still be easier than building an intake manifold and calibrating the carburator.
The main problem with d jetronic when in use can be the mechanical point contacts for the injection in the distributor, the rest is pretty reliable i would say.

Nabstud

Yeah the trigger points are one of my worries, I believe they are N/A.
1975 280S - Australian delivered

Nabstud

I've decided to not go ahead with this conversion. If it was a 4.5 I probably would have given it a go, not that I'm after a sports car but seems the only benefit I would get would be the V8 sound and the challenge of the conversion.

I'm parting out this car now, see For Sale section.
1975 280S - Australian delivered

celberg

350SEL is the rarest of them all. Not saveable?
350SL 1973
350SE 1975
SL500 1996

Nabstud

Too far gone, rust is in every corner, boot floor, rear window, C pillar, even had rust bubbles in the middle of the bonnet...
1975 280S - Australian delivered