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21-03-2014, 14:05   #1
pryantcc
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1971 Mercedes W108 280SE 3.5 V8 conversion to OM606 diesel.

I 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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21-03-2014, 17:38   #2
johnty56
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Very nice... would it be a shame to put a diesel in it? I have one of these and half the fun is in the set up.. I can't remember what the ratio is on the rear axle but how does it compare for a diesel conversion? Let me know if you are going ahead.. I might be interested in the engine!
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21-03-2014, 17:53   #3
pryantcc
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Very nice... would it be a shame to put a diesel in it? I have one of these and half the fun is in the set up.. I can't remember what the ratio is on the rear axle but how does it compare for a diesel conversion? Let me know if you are going ahead.. I might be interested in the engine!
Thanks for your interest. Definitely going ahead! I want to drive the car every day and I can't afford to do that on petrol at 16MPG!

I'm a bit reluctant to sell the original engine and 'box as the car would never be "matching numbers" again, but that reluctance may wear off as the budget stretches!

The rear ratio is indeed too short (3.46:1) for my conversion (the car will be slow), but I plan to put in a very tall ratio (.82:1) gearbox to compensate. I might increase the wheel size too if I need to, but the gearbox gets me back to the same kind of engine-to-wheel ratio as the original diesel donor car, so I'll see what its like once driving and decide then since the wheel change is relatively easy.
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21-03-2014, 18:19   #4
johnty56
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Whats the back axle like? Has the compensator been replaced with a spring?

I know what you mean about matching numbers, its probably better to hold onto it if you can and have space etc.. but if you are selling it let me know!

The car itself looks pretty solid.. the trim line on that model seems to be an issue with most of them along with some of the other Merc hotspots but that one looks good!
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21-03-2014, 20:39   #5
dgt
 
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This looks like an interesting venture! Where will you source the engine from?

I remember viewing a W126 which had a 307 engine inserted (another Merc) the owner said it all bolted up perfect
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21-03-2014, 21:17   #6
gctest50
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Very nice... would it be a shame to put a diesel in it? .............
depends
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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

Last edited by gctest50; 21-03-2014 at 21:24.
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21-03-2014, 21:38   #7
pryantcc
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This looks like an interesting venture! Where will you source the engine from?
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.
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21-03-2014, 22:14   #8
pryantcc
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Whats the back axle like? Has the compensator been replaced with a spring?
Yep, mine has a spring. It all seems pretty solid and robust! Should be well able for the standard OM606 setup.
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21-03-2014, 22:47   #9
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Would you consider convertijg to gas? It'd keep original numbers and you'd get better value economy wise
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21-03-2014, 23:49   #10
dgt
 
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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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22-03-2014, 00:05   #11
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22-03-2014, 02:23   #12
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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.
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22-03-2014, 20:09   #13
pryantcc
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Would you consider convertijg to gas? It'd keep original numbers and you'd get better value economy wise
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.

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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...
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!
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22-03-2014, 20:43   #14
quietsailor
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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.
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 storage

Last edited by quietsailor; 22-03-2014 at 20:47. Reason: had a quick google
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23-03-2014, 11:10   #15
Capri
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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 idea
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