Modern diesel engine in W116 280S? What challenges would I face?

[frahman7387]

Hi everyone,

My father is the owner of a 1979 280S (W116) and it is currently not running. Since it is a bit expensive to operate, and he has already poured lots of money into repairs to no avail, he is considering parting with it. As the car has considerable sentimental value, I have suggested installing a more modern, more economical engine to replace the original. The car is in Bangladesh, but was originally imported from the UK and is specc'd accordingly.

I'd like to know if there are any technical (structural, mechanical, electrical) challenges in putting in a 2.5L or 3.0L diesel engine with automatic transmission from either a C-class, E-class or S-class from the 1990's-present (such as the OM612 or OM642). This article says its possible, I want to know what challenges we'd face with a W116, since its an even older model.

I have looked through the MB club UK forum, but have not found anything detailing a diesel engine for a W116, just petrol engines (which were very illuminating btw!). I'd appreciate any wisdom, as it would potentially allow us to keep the car, something that I am very keen to do.

Thank you!!

--Farhan R

 

[brianbrian]

Hi you could use a 250d out of a 124 from1985 to1992/3 this would give you 40mpg plus ,but top speed would only be 115mph. Bolt the 250d engine to the 116 g/box so you do not have to mess about with the 116 propshaft or back axle. You will need to have aprox- 1/4: of inch taken of the 124d flywheel so the 116 torque converter will fit. Cut the cross member, move back 2inches so it does not fail the engine sump.You will have to make engine mountain brackets as nothing else will fit, I made mine out of wood as a pattern , then got a engineering company to make them in metal. Fit the 124d radiator ,make brackets top and bottom for the radiator, use 124d header tank and hoses. The wiring up for the glow plug relay and alternator, starter motor will be easy for any car electrian. You will use the 124d starter motor and alternator. you will need a vacuum switch so you can start and stop the engine, the 250d engine has its own mechanicle vacuum pump. Use the 116 petrol fuel tank, but do not forget to open up the filler pipe as the diesel pump nozzle is larger. You will not have to alter the suspension for the 250d engine either, Good luck Hope this helps

 

[wireman]

Re-vacuum switch for the stop pneumatics, there are on many modern turbo diesels a 2 way solenoid vacuum valve used to enable the turbo wastegate which would be an ideal candidate for converting the electrical to vac without disrupting the dash or steering lock.
Modifying the flywheel must be done with some degree of precision the dynamic balance is most important or the car will want to shake itself to bits. A workshop capable of setting up and cutting to better than 0.02mm tolerances will be best suited for this task. A session on a balancing machine might be of benefit once the cutting has been done to it.
I don't know which engine mounts are used in 116 cars but suggest that the 124 hydraulic type be used if it is practical to make the body brackets fit to them, they are very good at isolating the engine vibrations and of course match the mass of the engine.
Is the existing transmission an auto or manual? The 124 auto has a vacuum control valve on the fuel pump to generate the transmission control pressure which will connect directly to the tranny instead of the tranny being connected to the inlet manifold, some tweaking of the tranny's vacuum modulator might be required to get the gear changes as smooth as possible.

Sounds like a fun project, 602's seem to last forever if they get regular TLC and oil changes.

Welcome to the forum, go for it, and keep us posted, send a photo or two.

 

[MechPhil]

IIRC, the 617a turbodiesel was used in the US 116's, but that's hardly a modern engine. I wouldn't opt for a 612, as too many electronics are needed to manage the engine. The 602 does seem to be the very best choice for a good compromise between ease of conversion, performance and economy.

For a bit more punch, one can look at a 602.947 or.946, which is the 2.9 litre version as used in the G-wagen, giving 10% more power than the 2.5 version in the 124/201's. Also, be careful of turbodiesels, MB didn't fit turbodiesels to the RHD (as UK spec) 123/124/126/201 as the turbo wouldn't clear the steering box. I'm sure turbodiesels could be made to fit the 116, but a regular diesel would just be simpler.

HTH
Phil

 

[wireman]

I've had some further thought about this, I have some reservation of the torque converters characteristics from the original petrol installation being suited to the diesel engine, it will have different speed/torque ratios and will most likely have a different (higher) conversion ratio which might want the engine to turn faster before taking up drive and be able to overload the gearbox at start off, possibly ruining the diesels fuel economy advantage as well. Because of this and the manufacturer matched engine/converter and gear box control I would be more inclined towards a complete power unit swap in the interest of a more satisfactory and refined vehicle, this would entail modification to the rear cross member and its mounting to either the tranny or body and a special to the car prop shaft, cutting and jointing two halves from 116/124 would be practical but it must be balanced since it will rotate at upwards of 4500 Rpm at high road speed, it will I think be far more practical to find a decent prop shaft shop with balancing facilities than one for chopping at a flywheel.
Next question is, Is there is sufficient space in the transmission tunnel for the alternative gearbox and exhaust pipe etc? It is essential that however this conversion is done the axis of the new engines crank shaft and gearbox must lie in exactly the same place as the old unit, with a millimetre or so.
It will not be a good conversion if the prop shaft is put out of line by lowering/offsetting the power unit to make it fit in the space.

Anybody else got any thoughts on this?

 

[lwbnick]

300D out of a 124, no turbo to worry about and hardly any electrics.

 

[robparker]

Just email mb.v8conversions@btinternet.com
he has done many things like this.. turbodiesel into a 114, in a clk etc etc.. he'll tell you anything you need to know.