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560SEL engine in a 280S?

Started by 3l33ter, 03 June 2015, 04:06 AM

3l33ter

I recently bought a '75 280S, with the intention of swapping a v8 into it. The current engine works fine, but I'm interested in the M117 5.6L engine.

I've done countless hours of research over several weeks, and found only a little bit of information. From what I've read, it seems the M117 engine will install fine as long as I use motor mount brackets from a v8 w116 (450SE, for example) so I recently got a pair of those mounts. Initially, I would run the M117 without electronics, so it would be very inefficient but it would work. Later, I'll be converting to EFI with megesquirt. I want the 1987+ engines with higher 10:1 compression, and I'll have a custom exhaust with no cat (smog exempt). I'm happy with the stock 300hp but hopefully EFI and a freer exhaust would increase that.  8)

I'd love to see how it would compare against my 6.9!

One thing I'm worried about is the transmission. I still need to learn transmission codes... Will a 560SEL transmission work in my w116? Or would I need something else, like a tranny from a 450SE/SEL?

Will I need a radiator/hoses from a 450SE?
Should I get battery/starter cables from a 450SE?
Would the exhaust from a 450SE work? (To have something to start with.)
I know my differential ratio will be very short for a v8, I'll replace it. Before choosing, I have to see which transmission & gears I end up with.
I also know that the speedo wouldn't work with a w126 transmission - there are a few ways to deal with this.
According to my (rough) estimate of engine weights, the aluminum v8 will add 50lbs total, I think this is ok. I'll probably keep the front springs until I'm ready to go over the whole suspension.

Can anyone shed light on this swap? What else do I need to know? Thanks!
'75 280S
'77 6.9
'82 300TD

mirafioriman

I'd use the matching transmission and I'd fit the whole thing with its original electronics. I doubt it would run without the complete package. The ignition system is different for a start as is the fueling system. I've not personally done such a conversion but I believe that the electronics are pretty symple particularly if you buy a complete donor car to transfer things from.
I'm called Dave! I currently own: Mercedes W116 450 SEL 6.9, Mercedes W109 300 SEL 6.3, Mercedes W126 420 SEL, Fiat 130 Berlina, Fiat 131 Supermirafiori, Fiat 131 Panorama, Fiat 132 2000, Fiat Argenta and a Citroen Xantia.

s class

Certainly do-able. 

A 280S is really not an ideal starting point.  I have converted a 280S to a 280SE, and it required the ENTIRE wiring harness to be transplanted, which requires complete stripping of the interior including dash. 

You need to start with a 350 or a 450, in which case the conversion will be as close to plug-and-play as you can hope for.  Do a search on this forum, member roberd fitted a W126 500SE engine into a W116, and he described in some detail all the issues, and solutions. 


[color=blue]'76 6.9 Euro[/color], [color=red]'78 6.9 AMG[/color], '80 280SE, [color=brown]'74 350SE[/color], [color=black]'82 500SEL euro full hydro, '83 500SEL euro full hydro [/color], '81 500SL

oversize

Sounds like a great project.  The W116 was designed for a M117 and a 560 motor should slot in fairly easily.  Plus it would be lighter and more powerful than a 450
1979 6.9 #5541 (Red Bull)
1978 6.9 #4248 (Skye)
1979 6.9 #3686 (Moby Dick)
1978 6.9 #1776 (Dora)
1977 450SEL #7010 white -P
1975 450SEL #8414 gold -P

3l33ter

I was looking for a nice 450. They are getting harder to find in general, let alone a nice one. I told myself I would only bother with a smog-exempt model, so I looked for either a 300SD or a pre-1976. I went with the 280S because a nice 1975 came up with my favorite options: no sunroof and manual climate control!

Well, now you got me talking about my car, I might as well tell you more. :)
It has 108k miles, straight body, nice silver paint (not original), excellent blue interior, and no rust! I already have an aluminum hood and trunk from a 300SD which I'll put on after the engine swap. I also have some 1974 bumpers, which look more like the euro ones. OK, I'll start another thread about it later. Back to the motor swap...

Removing a dash is not a big deal for me. But with this car, I'm not too concerned with a factory-looking result, because I'm not keeping the m117 in stock form. I will likely make a custom engine wiring harness for a megasquirt computer, make some fuel rails, etc. Big project, but doable.

Thanks, I'll look up roberd.
'75 280S
'77 6.9
'82 300TD

oversize

What are you hoping to achieve with Megasquirt?  Sounds like a lot of money and effort for nothing.  Why not look into a Dkubus system for the factory CIS?
1979 6.9 #5541 (Red Bull)
1978 6.9 #4248 (Skye)
1979 6.9 #3686 (Moby Dick)
1978 6.9 #1776 (Dora)
1977 450SEL #7010 white -P
1975 450SEL #8414 gold -P

3l33ter

More power, more fuel economy, better technology, etc. I want to start by just getting the engine in there and working, then I'll see how far I want to go.
'75 280S
'77 6.9
'82 300TD

TJ 450

Sounds like a nice project. What you'll need is a 450SE parts car, because you'll need to transfer the entire wiring harness, as well as the fuel lines, and the rear axle to do it properly.

To use the 4-speed transmission that mates with the 560 engine, you'll need to modify the tailshaft and the transmission mounting.

You will also need to swap the injection system (fuel divider etc) off the 450 engine onto the 560. 560 has electronic idle speed control and does not have the provision for the old thermostatic auxilliary air valve, so you would need to modify the manifold or experiment and see if one off an early 500 M117 would fit.

You will also need to modify the transmission with the output housing off a W124 if it's possible, or fit a late W107 speedometer with electronic operation.

It's a lot of work, but anything can be done.

1976 450SEL 6.9 1432
1969 300SEL 6.3 1394
2003 ML500

3l33ter

Can you explain what is entailed in the transmission modifications?

According to some research, I've got a 3.69 rear end, and these are the different ratios available in the W116: 3.69 (280), 3.46 (350), 3.07 (450 and 300SD), 2.65 (6.9). I've read that W123 and early W126 differentials are compatible, but not late W126. Those cars have 3.69, 3.58, 3.54, 3.46, 3.27, 3.07, 2.88, 2.82, 2.47, 2.24. The 560 has a 2.65. I changed the differential in my 300TD from 3.07 to 2.47 to lower the revs, and I love it. I might use the same thing in the W116. But I might wait and fool around with the 3.69 first. :)

I'm on the lookout for an electronic speedo from an R107 SL. I also considered a frankenspeedo using W126 speedo internals, and W116 speedo housing and face. If new graduation is necessary I can print a vinyl decal for the faceplate.

'75 280S
'77 6.9
'82 300TD

TJ 450

All the V8 tailshafts have a larger up-rated flange and flex discs and if I remember correctly, and I'm pretty certain, the diff housing is smaller on the sixes as well... you'd have to check on that.

With the trans, it's probably easier just to use the electronic setup, but because the W124 still uses a cable and it's the same series of transmission to the W126, I believe you may be able to modify the rear housing....

Rear housing with mechanical speedo cable;


As there are quite a few differences between 722.3 and 722.4 transmissions this may not be possible, so it would be an experiment if you can find scrap examples of both transmissions.

Tim
1976 450SEL 6.9 1432
1969 300SEL 6.3 1394
2003 ML500