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1971 Mercedes W108 280SE 3.5 V8 conversion to OM606 diesel.
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21-03-2014 2:05pm#1I bought this car some months ago with a view to turning it into my daily driver. The plan is to fit a modern(ish) Mercedes OM606 diesel engine.
Structurally, the car isn't in bad shape although almost every panel has some rust issues ranging from very minor to disintegrating!
You can see the front suspension is just about absent in the pic below. The passenger door is not closed, the alignment is actually pretty good! The paint is pretty fresh, but bubbling through from underneath, so will need doing again.
Here's a close-up trying to show the bubbling above and below the trim strip. This is the worst patch for size, but I have issues on almost every panel. Around the rear screen is the worst I can see externally.
This is the inside of the passenger door. In their wisdom, someone blocked up the factory drain holes with filler and drilled new ones which weren't at the lowest point of the door!
The whole underside was sprayed with Schutz prior to sale. I've scraped off a couple of the rusty patches here, no surprises, I could see they were there before I bought it. It's mostly just surface rust which I'll blast off and re-paint.
The front screen has moisture damage also, so I'm a bit afraid of what I might find in terms of metal when I remove the windscreen rubbers!
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Very nice... would it be a shame to put a diesel in it? .............
depends
The 1998-model OM606 3L straight-6 has now covered over 400,000 km (just under 250,000 miles) so you could say it’s well run in.
........ is mated to a 5-speed automatic transmission from an E55 AMG. ...........the car also runs Toyota Aristo axles
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I've got one in a '99 E300 Turbodiesel. Problem is that it's a bit difficult to get the auto gearbox which comes with it working properly. You can get a controller to run it but it can be clunky at best. I'll be bolting on a manual transmission, there are plenty which fit, and it will help me with my final drive ratio.
If it's of any use, I have a M117 autobox sitting on a pallet if you're stuck for one. Having said that, the manual would appeal to me more!
Just to add, those engines take well to compounding and 4-500 bhp is a very achievable figure if that's of any interest...
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I've thought about this alright, but I'd still be running a 40 year old engine and really want to put some miles on this thing. I like the idea that spares for the diesel are readily available, as well as the spectacular reliability reputation.quietsailor wrote: »Would you consider convertijg to gas? It'd keep original numbers and you'd get better value economy wiseIf it's of any use, I have a M117 autobox sitting on a pallet if you're stuck for one. Having said that, the manual would appeal to me more!
Just to add, those engines take well to compounding and 4-500 bhp is a very achievable figure if that's of any interest...
Thanks, but I'm pretty fixed on the manual conversion for now. I've no plans to do anything in terms of power output. I'm aiming for economy and am more of a "Driving Miss Daisy" kind of guy. I'm very impressed by what these engines can do in standard form though, with just a heftier dose of fuel and a couple of turbos stuck on. It's incredible!0 -
I've thought about this alright, but I'd still be running a 40 year old engine and really want to put some miles on this thing. I like the idea that spares for the diesel are readily available, as well as the spectacular reliability reputation.
It's a merc - 40yrs old is nicely run in
, yeah i know what you mean, sometimes it's worth just pumping some big money into a critical part and having that peace of mind it won't let you down.
If your keeping the old engine and 'box have a hunt around the internetz and there should be storage procedures for long term storage. That way you'd have a perfect original engine if you ever want to sell her
Edit, here's a few pages form a quick google
Motorbike engine long term storage
MB long term storage0 -
16mpg /??miles per week / = €?? ,
Cost of engine/conversion/bits/time-labour = €??? , (not to mention the thought of returning it to 'matching numbers' in the future )
Is it REALLY worth your time and money doing such a conversion
Maybe I'm just getting older and wiser but all this 'DAYSEL,DAYSEL,DAYSEL' talk that goes on here REALLY gets to me - diesels need more servicing and parts and oil changes. Slower and dirtier as well - yet the country seems fixated on DAYSEL as the saviour of motoring. Compare a 300SD and 350SE V8 over 3 years, initial price paid, fuel AND parts costs etc and see what wins
In South Africa they replace diesel engines with petrol ones - now THAT'S a better idea0 -
What about a gas conversion? Too much labour in installing a diesel and its never going to be great in a car like that. I drove a 1980 450 sel 4.5 recently, a very nice car I thought but it needed work and Im not the man to do it or pay someone to do it (had invoices from South Dublin Merc specialist for 5k to change the distributor and fuel injectors and the problem remained, engine ran rough after car was gunned, I did a google and it looks like tank rust blocking the fuel pickup, one invoice was for 650 euros to change 18 circlips on hoses what that's around 2 euros in,parts and 648 euros in labour for a few hours work)
I think the owner gave up on it due to the unreasonable upkeep cost.
invoices from South Dublin Merc specialist for 5k , not sure these 'specialists' know what they're about - join a Merc forum and DIY is the best option 0 -
My commute is 478 miles per week, at €1.50/L for both fuel types, that's nearly €100Euro per week saved. The diesel does about double the distance to the same volume of fuel. However, if you add vegetable oil into the equation, it gets even cheaper.16mpg /??miles per week / = €?? ,
About €700 for the bits, doing the work myself, but it will certainly take a lot of time. I plan to be clever about any modifications, making them reversible where possible.Cost of engine/conversion/bits/time-labour = €??? , (not to mention the thought of returning it to 'matching numbers' in the future )
It's very well worth it, over a year, the conversion saves me about €5K in fuel alone, and that's without diluting it with chip fat.Is it REALLY worth your time and money doing such a conversion
How does a diesel need more parts? In my case, I'm eliminating spark plugs, HT leads, distributor, points, coils, rotor arm and electronic fuel pump. I'm replacing them with glow plugs.Maybe I'm just getting older and wiser but all this 'DAYSEL,DAYSEL,DAYSEL' talk that goes on here REALLY gets to me - diesels need more servicing and parts and oil changes. Slower and dirtier as well - yet the country seems fixated on DAYSEL as the saviour of motoring. Compare a 300SD and 350SE V8 over 3 years, initial price paid, fuel AND parts costs etc and see what wins
I'll have about 170HP and 330Nm of torque at just 1600RPM. That's plenty for my requirements!0 -
I've been working on the front suspension. The whole lot was removed, blasted and primed where required and new bushes/bearings, etc fitted.
This was the rustiest bit, some corrosion worth stopping.
Springs and brake backing plates were scruffy looking too. Turned out both backing plates had stress fractures, so I'll weld them up before re-fitting.
I only blasted the spring turrets on the subframe as they were the only rusty parts.
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Work is progressing slowly! I'm in the process of going through the wiring on the donor car to make sure that once the engine is removed, everything will still work. So far, things are going well, but its a very slow and painstaking process, particularly since I'm paranoid!
Here's the donor car, a 199 300E Turbodiesel:
And the power plant. It's had some boy racer treatment, but doesn't seem to have suffered too much abuse, it still runs very well, lovely and clean.
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I'm very excited, I've finished the electrical strip down, wohoo!
I can make the engine run now with only 4 12V connections and 2 fuel pipes. It's such a relief as the electronics are the part I was most worried about for the whole job. I just have 2 permanent 12V feeds, 2 which are switched by the ignition key and 1 for the starter solenoid. Its very satisfying.
The wiring all still looks a bit of a mess but I can tidy it up once I see where to put everything in the project car.
This spaghetti is mainly the old instrument cluster connections (I hope to find a tacho and glow plug indicator light in there) and the computer diagnostic port connection.
On the other side of the donor engine bay is another box of tricks, power for the ECU comes from here and some other stuff.
The interior isn't looking great. It turns out I didn't need anything from in here and could have left the dash intact, but I needed to get in there to trace some wires in order to learn this! I'll know for the next one ;-)
So, this is it with all the required electronics sitting on top of the engine. Attention now moves to the mechanical strip down!
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Another big step along the way. The donor engine liberated from its former home. The auto 'box is going to a new home elsewhere and I've ordered what I hope will be all that is needed to add a flywheel and cluch. Time will tell!
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I bought a bunch of brownie points with an iPad last week. I've been cashing them in hand over fist over the long weekend, and made some more good progress!
The old 280SE was very reluctant to give up its 3.5L V8. It looks like the designers intended for the engine & 'box to come out through the bottom of the car. Well, I don't have the head room nor the equipent to get the car that high up, so I had to pull the gearbox out from under the car and then lift the engine straight up. It was a real pain getting it all out as every electrical connector was corroded solid, the bolts holding the 'box to the engine were all but inaccessible, the exhaust joints had all rusted solid and I couldn't upen the connections to the oil cooler and didn't want to cut them.
Anyway, it's out now!
I haven't made a detailed study yet, but some stuff I've found out over the weekend:
The 280SE engine bay is about 3cm narrower than the E300 donor car. This shouldn't be a big problem.
The manual gearbox I intend to use is about 11cm shorter than the auto I'm removing. no problem in terms of mounting, but I'll need to extend the prop shaft to meet it.
The rad from the donor is way too big. I'll wait to see what space is like with the new engine fitted before doing naything drastic, but I might have to go buy an aftermarket one.
It looks like the steering box in the 280SE is enormous and might get in the way of the exhaust, but again, I'll see what its like with the engine fitted. I might even explore the possibility of insalling the rack out of the E300 if it works out anyway handy as the old steering box is incontinent and making a mess of my garage floor.0 -
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This is going to be a long post, I hope I've explained what's going on well enough for others to replicate it if they want to!
I'm not sure what you call this plate, but this is the original plate which had the ring gear attached to it and sat behind the torque convertor. You might or might not be able to see there are 6 tabs protruding from it which whizz past a sensor which I guess is for an engine speed feed to the ECU rather than a crank position.
The ring with the tabs on it looks pretty crude, but it was obviously machined after being welded on to make it perfectly circular, at least on the outside!
Anyhow, that bit is getting dumped as I'm changing to a manual gearbox. So, I bought one of this on a wing and a prayer. It was listed as a dual mass flywheel conversion kit for a Merc Sprinter van, 2.2CDI and others from 2002 to 2006:
It contained all of these bits:
The first problem I encountered was that there is a protruding flange on the end of the crank shaft, and a corresponding recess in the flywheel. The flange was 11.2mm and the recess only 10mm. This meant that the flywheel could not be tightened right up against the end of the crank, so the crank shaft flange was duly ground back to be shorter than the recess in the back of the flywheel.
Problem number 2 is that the new flywheel is completely surrounded with ribs which, I can only suppose are used to generate a signal for the Merc Sprinter it was intended to be used in.
These ribs also slightly contact the sensor. Plan "A" was to machine away the ribs I don't need in order to leave 6 remaining, simulating what was in place before, I could then put a spacer behind the sensor so that it didnt stick out so far and wasn't hit by the remaining ribs. The main issues with plan "A" were that the ribs weren't in the same place on the flywheel as the tabs on the original item (I'm not absolutely sure that there isn't some kind of timing function along with RPM!), and that I would then need to have the flywheel balanced.
I have a great engineering friend who came up with a far superior plan "B": We would drill the 6 'valleys' which correspond to the tabs we had removed, tap them and screw in bolts which would protrude above the existing ribs. We'd have to move the sensor even further out, but that's no big deal, and we wouldn't be disturbing the balance of the flywheel. So, to the implementation of plan "B".
We marked the valleys which were to be drilled and tapped, then mounted the flywheel on the engine. We turned down a big bolt so that it matched the shaft size of the sensor and would fit snugly in the sensors mounting hole. We then drilled a hole down the centre of the bolt and poked the bolt into the sensor hole. Now, we had a guide which we could use to make sure the holes we drilled were directly beneath where the sensor would be.
Here's the sensor fitment:
and the bolt we guntered into a tool:
and some drilling underway:
Here's a bolt inserted in the hole. I plan to get longer bolts, loctite them home and then remove the heads so that the part left sticking out proud of the ribs is closer to the 5.5mm of the tabs which were originally present.
Aside from these alterations, Everything else seems to work out in terms of the position of the bearing which accepts the end of the spigot shaft, the position of the clutch friction plate in relation to the splined part of the spigot shaft, and the position of the pressure plate in relation to the release bearing/concentric slave culinder which is mounted in the gearbox. Happy days!0 -
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Well, plan B turned out to be a bit of a disaster! I attached the modified flywheel to the engine, and after setting the height of the RPM sensor so that my newly attached studs didn't hit it, we hooked up fuel and sealed up the oil & water pipes after a emptying a can of water in and seeing it flow across the floor! My self and a friend hoisted the engine up on the engine crane, hooked up a battery and hit ths starter. There was the usual click of the starter followed very closely by a thump, and the engine was locked solid!
It turns out that it isn't just the gear on the end of the starter which pos out to engage with the ring gear, most of the end of the starter comes with it!
So, while the starter was engaged, the studs would whack straight into it and the flywheel do no more than 1/6 of a rotation.
Plan A was re-hashed to become plan C and required some more extreme flywheel modification. The studs which we had inserted were removed with great difficulty. The Loctite we used had "Extra Strong" or something along those lines written on the bottle. It was amazing, the studs were locked solid after only an hour ror two! So much so that 2 of them broke off when trying to get them out!
My friend set the flywheel up in his lathe and cut down all of the ribs from around the outer edge, then fitted new studs in the old holes and turned them down to the appropriate size.
Here's how it was before:
And after:
And a closeup:
Now the flywheel is re-attached, the RPM sensor located appropriately and the engine runs suspended from the engine crane! It's a bit cold, and smoky as a reslt, but works fine.
I don't know how to embed a video, but you can see the startup on youtube here.
To say that I'm a happy camper would be an understatement! So, now on with the rest of the work: making engine mounting brackets, making clutch pedal assembly, adapting drive shaft, etc...0 -
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Well, here it is, the "new" engine in its new home. It's only sat there, but it fits in well. The engine bay looks a bit empty but will soon fill up with a battery, air box, computer box and screen washer bottle. the blue shopping bag contains the wiring harness for now!!
This intercooler pipe had to be sacrificed as it was sitting on the anti-roll bar, I'll just re-route it, or might even get away with squashing it a bit:
Lots of clearance between subframe and sump:
And the exhaust clears the steering box:
It's difficult to get a decent photo of it, but here's the attachment for the shifting mechanism on top of the gearbox. It's pretty tight to the top of the transmission tunnel. That long self-tapper is someone else's legacy!
This photo shows the original V8 engine mount and the new, improved wooden version.
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