Want to put an M110 from a W116 into a W123, parts list?

[Admiral Ahani]

I have a W116 280S with the venerable M110 engine. The engine is fine, but I have an M117 V8 that I'm going to put into it.

I also have a W123 300td with a really tired engine. I've always wanted it to be a gasser (let's not go off-topic debating diesel vs gasser), so I figured I'd swap in the M110 from my other car, since that engine is perfectly fine and the W123s came with that engine anyway.

So before I jump headfirst into this, what do I need to know?

In particular, what parts from the W116 will not work on the W123? Finding a W123 280E at the junkyard is becoming rare, but there is one right now, so I could go grab the parts that I need. Are the engine mounts different? Radiator hoses? Transmissions?

What else would I need from the W123 gasser to convert my diesel? Throttle cable/linkage? Driveshaft different?

I'm prepared to do any and all fab necessary, but I figure this should be 99% bolt-in. TIA!

[Mike D]

Originally Posted by Admiral Ahani

I'm prepared to do any and all fab necessary, but I figure this should be 99% bolt-in. TIA!

Made me chuckle.

Short incomplete list: Engine arms, exhaust manifolds, fuel pump and attendant lines, depending on the year of the donor engine possibly the ECU, torque converter, transmission or at least the valve body, throttle linkage from the pedal forward, ignition switch.

How are you going to deal with the SLS?

[Frank Reiner]

Originally Posted by Mike D

Made me chuckle.

Short incomplete list: Engine arms, exhaust manifolds, fuel pump and attendant lines, depending on the year of the donor engine possibly the ECU, torque converter, transmission or at least the valve body, throttle linkage from the pedal forward, ignition switch.

How are you going to deal with the SLS?

-As Mike has noted above, the engine mounting components and the exhaust manifolds are chassis specific.
-The complete engine & transmission from the W116 can be moved directly to the W123. The M110 w/722.1 combination was used in both chassis. (The 722.1 was not used with the M117, and so will not be retained in the W116 chassis.)
-The SLS pump is driven by the front of the exhaust cam when used on a M110. The drive dog is a bolt on piece. The cam box has a cover at that location.
-The transmission may be located slightly farther back in the W123 chassis with the M110 vs. the OM617. The drive shaft may have to be shortened.
-Final drive gearing will need to be shortened to a 3.07 in combination with a !st gear start in the 722.1, or, a 722.2 trans could be used to provide a normal 1st gear start.

[Admiral Ahani]

Thanks for the input guys!

OK 99% was a euphemism for "there are parts to make it bolt-in if I want it to be" but I will be fabbing a bunch of stuff while I've got the car apart.

I've done engine swaps before so I know how even a "straightforward" swap can have lots of minutia that bogs you down. I can see this one being like that. But on this car I'd rather cheat and fab certain things than get really extensive with changing things over.

Exhaust: I want to make a custom exhaust, so I don't really care which headers (i.e. exhaust manifold) I have. I'll likely cut the downpipe flange off and from there on down will be new. I would think that the headers are not chassis specific, but even if they are, I don't think it would make much of a difference if I'm making a custom downpipe etc. Please correct me if I'm wrong.

Transmission: So I can use the w116 transmission? Awesome!

Driveshaft: I figured as much, so I'll try to get one from a w123 280e.

Differential: My w123 currently has a 2.47, and my w116 has a 3.69. I think I'll end up swapping these, but if changes are needed I could source a new diff pretty easily. (I still have my w123's original 3.07 as well.)

Fueling: Do I really have to change the lines? I thought it might be easier to adapt the existing diesel lines and add an aftermarket inline pump and filter back at the tank. But I might as well check out 280e parts to see if they'll be easier to use.

Engine management: my M110 is carbureted. I haven't decided if I want to leave it that way or convert it to TBI and MS. I feel like the latter would make the swap a lot easier, and it's in the long-term plan anyway.

Ignition switch? Didn't realize about that one - is it different in a gasser?

SLS: I was planning to delete the SLS. Mine works fine, but I'm one of those guys who wouldn't miss it. But are you saying that on the M110 the head and camshaft are ready to drive an SLS pump already? So I just need to buy the drive dog and the SLS pump? Is there any chance that those parts can be taken off of my OM617???

[Frank Reiner]

Ensign Ahani:

Re:
Fuel lines. Use the existing supply & return lines. Connect the engine driven diaphragm pump to the supply line. No additional pumps required for carbureted operation.

Management. Carbed is simplest for initial operation.

Switch. The switch for the diesel engine has a vacuum shutoff section added; the electrical section should still have the ignition circuit contacts.

SLS. The pump is the same; reuse the pump from the diesel. The drive dog might be the same.

[Mike D]

The M110 exhaust is already a free flow style with exhaust separated into two banks hence the need for the exhaust change/modification.

Regarding the fuel system, I was thrown off by your mention of a 280E. You would only need to do a bit of line altering to use the existing steel lines in conjunction with an electric pump for carburetor or TBI.

95% of the parts are already there between the three vehicles. I just didn't want you to think it was just a "take this engine out and put that engine in" kind of deal. It sounds as though you've been down this road before and you have a grasp of what is involved.

I'm sure you've seen those,"Car apart for restoration, don't have the time/money/space to finish, all parts there" ads. In other words, someone took on a project they didn't realize the amount of work and time involved.

[Admiral Ahani]

Originally Posted by Mike D

95% of the parts are already there between the three vehicles. I just didn't want you to think it was just a "take this engine out and put that engine in" kind of deal. It sounds as though you've been down this road before and you have a grasp of what is involved.

Yes, been down this road with VW golfs and Porsche 944s, but this will be the first MB so still learning some of the little details.

Originally Posted by Mike D

I'm sure you've seen those,"Car apart for restoration, don't have the time/money/space to finish, all parts there" ads. In other words, someone took on a project they didn't realize the amount of work and time involved.

That would be my 6.9 I'll get that done... someday...

Originally Posted by Frank Reiner

Ensign Ahani:

Re:
Fuel lines. Use the existing supply & return lines. Connect the engine driven diaphragm pump to the supply line. No additional pumps required for carbureted operation.

Management. Carbed is simplest for initial operation.

Switch. The switch for the diesel engine has a vacuum shutoff section added; the electrical section should still have the ignition circuit contacts.

SLS. The pump is the same; reuse the pump from the diesel. The drive dog might be the same.

Thanks.

[Admiral Ahani]

Anyone know what the weight difference is between the OM617 turbo and M110? Maybe I should try to get the front springs from a 280E.

Is the oil pan on a M110 the same between the W116 and W123?