There are a few questions about this topic, so I thought I would try to help some people out with what I have learnt so far. First, a disclaimer! I do not profess to be an expert on mechanical things, but I am having a go at this myself, with lots of help from various people in Oz and the USA. Hopefully I remember all the main points, but if something sounds wrong, please raise the issue as I may have forgotten something! It has been about a year now...
I am working on such a project myself, fitting a motor from a 1980 W116 450SE into a 1965 W111 220SE. Currently I am putting the car back together after getting it back from the painters, so it is an empty shell. But I have had it all together to check for how it all fit together.
Firstly, you can check out some pics in drew56cus/Finny build-up - Photobucket - Video and Image Hosting
. Start at page 3 and work to the latest images...
I got a W108 280SE 3.5 (we didn't get the 4.5 version in Australia). The guy I bought the parts off put a good W116 4.5 motor in it for me. The W108 front subframe and diff are bolt in transplants for the W111. The W108 V8 cars have larger disc brakes on the front - get the ventilated ones. But you will need to run 14" wheels. Just unbolt the entire member from the donor car, and transfer it to the finnie - with new subframe mounts of course. You don't have to swap this if you don't want - the V8 will mount up to the finie front end - but I want the car to work as a system, and MB designed bigger and better brakes for the faster motor - so I recommend you make things safer by getting the better brakes.
Take the diff from the W108 as well, as it has a lower gear ratio to suit the V8, plus it has disc brakes (and is stronger - you will likely blow up the finny one with a V8). Now, some of the W108 disc brake cars have a valve in the lines near the rear - if your donor car does, take it and swap it across. Apparantly drum brakes need some pressure in the brake lines on them all the time to work, whereas discs don't, so there is a difference there. *** If anyone can explain this better, please do!!***
The rear of the gearbox - in particular the flex disc - will hit the tranny tunnel in the finny. See the pics. It only just hits a small part of the tunnel just forward of the body crossmember under the front seats. However, if you want to use the factory floor shifter, then it needs a cutout at the front of the body crossmeber. And also, the W108 driveshaft has its centre bearing about 8" forward of the finny. Now, I could have gone for a cable operated shifter and just bolted it to the floor wherever I liked, and I could have stitched in the driveshaft centre bearing mount where it was needed (or got a new driveshaft made up), but I wanted the car to be like MB had made a V8 at the factory. So I cut a big piece of the floor and tranny tunnel out of the donor W108 that had teh larger tunnel, the shifter mount position, and the centre bearing mount, and transplanted it all in. There are some spot welded floor pans that you can unpick to make this easier (I learnt this later!). And be careful cutting the floors out, as I bumped it when I did it, and ended up needing some little extra filler panels. Oh yeah, and make up a template for the seat mounts, as you will lose them when you transplant the tunnel section.
So now the engine and trans can be bolted in place like it should. Now you need to modify the throttle system so it works. My 4.5 was K Jet, but the W108 is D Jet, so the systems are slightly different. I transplanted a bracket off the firewall of the W108 that a throttle linkage pivots off - see pics. And then I cut down the original rod with the lever arms that push the linkages to suit - again, see pics. Hard to describe when I have no idea what the bits are called!!!
Oh yeah, you will need the W108 V8 power steering box, as the pipes on it have a different configuration to avoid the exhaust manifolds (boy are they close - if you have bad engine mounts, the exhaust will hit the top of the box).
Um, there is some wiring to do to hook up the K Jet brains - haven't been given that detail yet by my advisor, though he assures me it is not too complex considering my car was a SE to start with. Anyone done this bit yet??
You also need the W108 V8 fuel pump.
Radiator - I am going to run the W108 radiator without the oil cooler. It is similar in size to the finny one, but taller. I got a radiator shop to change the sides of the radiator for the W111 ones, so then I could bolt it in like the finny one. But I had to lengthen the mounting slots that the radiator bolts into on the side of the finny as I needed to move the radiator to the front of the car a bit. You will also need to slice off the top part of the radiator surround panel - have a look at a W112 300SE - you basically want to do that (the 300Se motor is a bit longer than a 220). I have some pics at home here if anyone needs to see them...
That is all I can think of for now. No doubt I have forgotten some things. Now, if it seems daunting, don't be scared - this is the first car I have built up, and whilst you make some blues (ah, that is a mistake for the americans out there), you should only make them once, and learn from them. But it does take a bit of time.
Anyway, hopefully this has been of use to someone, and I hope some others have a go at it too!
Cheers, Drew in Oz