1971 Mercedes W108 280SE 3.5 V8 conversion to OM606 diesel.

A long time since the last update so a long one to catch up! I spent a long time getting the auld Hilux through its test, doing some house alterations, parenting and that kind of thing! A few bits and pieces have still been done on the car. I've made up some brackets to change the old lever/rod operated throttle to a cable one for the throttle position sensor.
This is the new bracket to mount the sensor in the engine bay.





This bracket is fot the other end to hold the outer casing of the cable. Some rustiness in the bacground which will need to be dealt with!



The clutch pedal and master cylinder are in. They are from the gearbox donor clk. The fluid line to the slave cylinder is routed on the inside, but I still have to sort it out on the outside. It connects with a length of flexi hose coming from the gearbox housing.





In other news, I've done some work to get the engine into its final position. My resourceful and very talented engineering friend made a mounting bracket for the gearbox. The OM606 engine is rotated to one side so that is isn't so tall in an engine bay. Although the bell housing on my gearbox fits the engine crank case, the engine the gearbox was attached to mustn't have had the rotation because my gearbox now sits at an angle as you can see in this photo. The steering componenets are horizontal, the bottom of the gearbox is not!





The gearbox bellhousing could be cut and rotated to straighten out the gearbox, but I'm going to just leave it as it is. It doesn't look like it will present any mechanical issues with the build. I'll be crossing my fingers a bit regarding internal lubrication....

Here you can see the new bracket before painting and in its final position in all its glory!







Once the rear of the gearbox was fixed in position, the engine was nudged around the place in order to get the drive shaft to line up correctly in the centre of the carrier bearing:





Now that that's done, it was a case of trying to make sure the engine ends up in the same spot once the new mounts are fitted. So, there are two dots on the sump which line up with two ends of a piece of TIG wire. Once the new mounts are made, the engine should settle back into the same spot. That's the plan anyhow!





That's it, the Engine mounts shipped last Thursday, so once they arrive, it'll be a matter of figuring out how much they will compress under the weight of the engine, and making a mounting plates to suit.

There's been a major push the last few weeks. I'm sorry to say I've very few photos. Plumbing has been a large part of the work, there was quite a list:
Feed for clutch master cylinder
Intercooler
Oil cooler
Radiator
Power steering
Oil pressure gauge
Temperature gauge

The clutch master cylinder was the easiest part, just a length of hose from the brake reservoir down to the master cylinder.



The intercooler needed a custom pipe to be welded up to get down around the alternator and the anti-roll bar. the intercooler itself isn't permanently attached yet, but fits well between the two front bumper mounts.



For the oil cooler, it was a bit more involved. In the original car, the oil cooler is actually boldted onto the right side of the radiator, in line with it, so, apart from being unboltable, it is effectively an extension on to the side of the rad. The biggest problem with this was that the oil cooler plumbing on the new engine was on the left hand side. In order to move the cooler to the other side, we had to de-solder the sides off the rad and swap them around. You cna see it in its new position on the left of the rad in this photo:



Once this was done, it was clear that the top connection on the cooler was going to interfere with the power steering pump.



The solution was to swap the outlet position with what used to be the drain plug as the cooler is now upside down. So, we cut the fitting off the W210 E300 oil cooler as there was more meat in those and welded it to the oil cooler from the W108.

The W210 oil cooler:


And the swap job on the W108 cooler:



Once this was all sorted out, the only requirement was to extend the oil feed lines slightly to reach the cooler.


The top connection on the rad is very close to the outlet from the engine, so a bit of bodgery was required to get them connected. I got a couple of tight bends and cut and joined them. It's a little rigid as the engine moves about under power, but I'll try to sort that out by spreading the two halves on the joiner.




The power steering was probably the most awkward to sort out. In terms of plumbing, the guys making up the hydraulic pipes had nothing that would fit the pump end. So, my good welding friend cut the original pump connector and welded it to the hydraulic fitting.









Now, I also knew that the pump output would produce about double the pressure of the old original one, so presumed that hooking my more modern version up to the ancient steering box would result in bad things. So, I bought a gauge for £7.50 from Ebay, and, welding ecxpertise was required again to put together a fitting so that it could be connected to the end of the high pressure pipe.





An evening of testing followed. The pump registered just over 100 bar at the start and I was aiming for around 60. There is a pressure relief valve inside the pump body, a very simple arrangement with a spring that holds a ball bearing against a seat until the pressure pushes it off the seat against the spring. There were a few shims in it, so I went about adjusting with shims. The first try had only minimal impact +/- 2 bar, so adjustment was acheived by shortening the spring with careful application of the angle grinder! 3 or 4 tests later and the pump was outputting about 60 bar.


More welding was required to fit the engine oil presure gauge. There's a nylon pipe running to the back of the pressure gauge in the dash which feeds the pressure up to the mechanical gauge. The diesel engine had a handy bung at the base of the oil filter housing which was removed, drilled out and welded to the fitting from the petrol engine.

The temperature gauge is a vial on the end of a capilliary tube which runs to the back of the dash. The fitting from the petrol engine went straight into a handy hole which was plugged in the diesel without any modification.

If you're still reading, fair play! Here's what I'm getting around to:



It works!! The first time in about a year she's moved out of the shed! The drive went well. Gearing is very low as was expected, but I'm very happy with the way the engine behaves. It's hard to tell what it'll be like until you have it on a manual gearbox, but it's great. Clutch and gearbox work nicely too. I'm very happy and really like it. I'll try significantly bigger wheels and tyres shortly. According to my calculations, +2 inches in diameter will have me cruising at 70 and 2,400RPM.

I've been lacking with updates as seems to be a theme with this write-up, but, thankfully not because no work has been going on!

I've been having (anticipated) trouble with rear axle ratios. When I test drove the car, the gearing was very low, as expected. in 6th at 35-40mph. I tried running on wheels/tyres with a 2 inch larger diameter, but even this didn't make a significant enough difference.

The original W108 axle has a 3.46:1 ratio. There are versions from the 6.3L 300SL that have a 2.82:1 ratio, I think. However, these are rare, and accordingly expensive. Also purchasing one over the internet comes with a lot of risk as they are probably all more than 40 years old at this point. I looked at the idea of just putting in new internals into my existing axle, but failed to find anything that would fit easily. It quickly came down to having to swap out the whole axle for something more readily available with an appropriate ratio.

I already had the rear diff and subframe assembly from the 1999 E300 (W210) car that donated its engine. That has a ratio of 2.88:1, however, some quick measuring tape work established that it wouldn't fit between my chassis rails on the W108. Some further googling uncovered a sketchy report that someone had fitted a subframe from a W203 and although I couldn't find a write-up on the job, the photos looked like it hadn't been too troublesome.

I found a complete W203 sub-frame from a 270CDI for 120Euro. It wasn't in awful condition, there were a couple of joints and bushes that needed replacing along with the brake backing plates and it needed cleaning up, but was structurally sound. Brake discs, callipers, CV boots, etc. all looked good. Most importantly, it had a suitable ratio in the diff of 2.65:1

The original W108 axle was removed, and the bracket attached to the car floor that was used to stabilise it laterally was cut off to make room. It became apparent early-on that 2 things weren't going to work out. The first was that the wheels would be too close together to clear the inner rear wheel arches. Nothing some appropriately sized wheel spacers wouldn't solve. The second issue was that the front-top suspension link was going to foul the chassis rail on each side. After much head scratching, it was decided to just remove these links until the whole thing was fitted and then cut and strengthen the chassis rails by the required amount. It's a pity to have to do this, but there should be great benefits from having the modern multi-link rear suspension rather than the old swinging axle setup.

There were some good points too. The subframe fits quite well into the existing floor pan without any chopping of the car required aside from the chassis rails mentioned above. The shocks looked like they'd line up with the original top mounts well, and there was room for the new spring seats to go in without anything being in their way.

Thinking about how to fix the subframe in place, the rear was relatively straight-forward, just a cross-member to add with two spuds sticking down from it. This was chopped from the W210 donor car. The front, however, was completely devoid of any siutable anchor points, and of space to add anything as the rear seat footwell interfered with anything that could be added. I have a great friend who's been helping out throughout this build and he came up with the idea of butchering the W210 subframe in order to take its front mounting points and add them to the front of this W203 one. That would make teh W203 subframe longer and enable us to fix it to the structural points where the original axle had been fixed.

So, two front "arms" were cut from the W210 subframe and welded to the W203 item with a lot of reinforcement being added to make sure they would stay put!

I've managed to delete all my photos of the process, so I've stolen an internet photo here to try to explain what went on with a picture. I'll upload a proper one when I have the subframe off the car again, but for now, this will have to do. This is not to scale or anything and there's loads of extra reinforcing gone into it, but this gives you the idea:


Two mount points were added to the car for these to bolt up to. An enormous amount of care and attention went into the location and alignment of these fittings so that the subframe would end up in the correct horizontal plane as well as being centred properly in the car at the same time as having the line between the two rear wheels perfectly perpendicular to the car's mid-line.

Once the two front mount points were done, we bolted the rear cross member to the subframe and bolted it up to the front mounts. This gave us positioning for the rear cross member which was duly welded up to the boot floor.

Now that all 4 subframe mounts were sorted, we could turn our attention to shock absorbers and springs. The position of the lower shock mounts meant that they couldn't be mounted up inside the existing shock turrets as we had hoped. They hit the edge at the bottom of the turrets. So, I bought some short shocks (VW Type 2 van itmes) and we made mounts for the tops of them that were fitted inside but near the bottom of the turrets. The bottom mounts just had to be drilled out from 10mm to 12mm. The upper spring seats were already part of the rear cross member section that had been removed from the W210, so that aspect actually worked out well!

As mentioned earlier, the upper front suspension links would hit the chassis rails when the suspension was compressed. So, now that the subframe was in place, we could figure out how bad it was and cut sections from the chassis rails to compensate. The chassis was cut, re-made and plated on both sides of each rail to add back the strength that had been removed. You can see in the photos below how much was chopped and why.
Before:


After:


The inside of the chassis rail looked in reasonable nick in this area which was encouraging:



Next we turned our attention to the prop shaft which needed to be shortened a little and be adapted to somehow attach it's 4 hole UJ flange to the 3 hole job on the new rear diff.

The hubs, new backing plates and callipers were all blasted and painted in the hopes of preserving them. They were then re-assembled with new bearings, bottom bushes and handbrake shoes and look like this:




I've struggled to write this update and keep interesting without making the work sound easy. Believe me, this was not a pleasant nor an easy job. We met problems everywhere. The mounting spuds on the W210 rear cross member didn't fit in the W203 subframe mounts and had to be chopped off, turned down on a lathe and re-attached. The outside of the W203 subframe had to be chopped to wihin an inch of its life to fit between the car's chassis rails. The W203 hubs needed their bearings and lower bush replaced. The two front suspension links on the subframe which are used for adjusting rear tracking were seized in place and had to be cut out. The new brake backing plates were too big for my original 14 inch wheels so had to be modified to fit. The drive shaft was too long for our lathe which made alignment a nightmare when welding it back together having shortened it. The drive shaft flange (which was attached to the rear universal joint) didn't match the input flange on the diff, so a custom adaptor job had to be made up. The newly made exhaust had to be re-designed to go around the subframe and the back box shortened by about 1o inches. The handbrake cables were too short and had the wrong fittings on the ends, so we had to modify the hubs to take the original W108 cables. One of the W203 callipers was badly seized so the W210 ones were used but these wouldn't fit inside the wheels so we took the angle grinder to the pad wear sensor mount point on the callipers. This meant using the W210 disks but these rubbed the backing plates so had to be adjusted slightly to fit.

Update time!
Mechanical work is essentially complete except for some aesthetic work to make the rear axle conversion look nicer. Next step is to patch the rusty bits. With this in mind, everything is stripped again and the car was moved to my friend's place for him to do the welding. We left the axles under it for ease of transport and loaded it onto the trailer for shipment. I could have towed it but had removed pedals, etc so was without brakes.


I forgot to photograph the new engine mounts at the time and the engine has been on top of them since, so here's a picture. These 2 beefy lumps of plate are welded to the front subframe just inside where the original engine mounts were and the rubber mounts bolt onto them.


Once moved, I adapted the front seats from the donor E300 Merc to fit the original seat rails. The old seats are pretty tired and don't have headrests, etc. The colours match and the more modern ones don't look too badly out of place. The floor needs a good bit of patching and removal of some old bodged repairs and it was always the plan to put the car on a rotisserie thing so it could be spun. After a very brief look online at the prices and quality of what is available, we decided to make our own. My welder friend knocked it up from scrap in just 3 evenings work!






The car will be mounted to it by the bumper mounting points. In readiness for lifting I took off the doors and front wings. The axles will be left behid as it's lifted onto the rotisserie.

Work continues! I had a batch of small bits and pieces ready for blasting and painting.



The power steering box was one of them. It had always been leaking so I bought a seal kit and stripped it down.
I blocked up all the holes & blasted it along with my other brackets, suspension arms and small bits. It wasn't until I was geting it all ready for spraying that I noticed what seemed to be an oily patch on the outside of the steering box casing.




It turned out to be a hairline crack!



It also turned out that the steering box is made of cast iron which apparently doesn't take too well to welding due to differences in expansion and contraction rates in response to heat. So, I took it out to my welder friend to see what he could do. We ground out the crack and heated the whole lot to about 300 degrees Centigrade. He then TIG welded it up and we stuck it back in the oven to cool slowly overnight. Thankfully it hadn't cracked when examined in the morning!





Now it's back in the queue for blasting and will be painted up and re-assembled with new seals.

Things have slowed down over the summer and I've given up all pretence that this is just an engine swap, it's a full blown restoration now, for sure! Hopefully I'll have a little more time now to put into it, things are already starting to move again.

The focus at the moment is on the bodywork. There is a bit of a combination of replacing previous bodging as well as chopping out virgin rot and replacing with good steel. Having the car on the spit is absolutely fantastic, a huge help and makes things far more convenient, particularly for the underneath.

So, work started on the passenger side sill area. You can see plenty of metal was chopped out, most of it previous mess:



This is the back end:


And some detail. There is good metal in there, you just have to dig a bit to get to it!



Some patches going in:



Then, once these were done, we wheeled the whole setup outside and blasted the inside of the sill and everything we could get at, painted it all with epoxy and coated all of that with cavity wax. I should say that the jacking points have been intentionally deleted. I didn't like having holes in the sills for them and I can just carry a little bottle jack for changing wheels and jack off some more robust areas. I've no photos of the blasting process, I'm afraid but just imagine lots of dirty lookin stuff, then dust, then nice painted stuff, then this:



It's nice to know the upper sections of the sills are well protected by applying all the goop with the car upside down.


Then to buttoning it all up:



The inside of the sills will be given more cavity wax with the car the right way up to coat the inside of the sill bottoms, and when the whole bottom side of the car is done, the exterior will all be blasted and coated with epoxy primer.

kizmax wrote: »

I guess I assumed a merc to merc transplant might be the easiest
Can you recommend which model is the handiest

Hi, I can't recommend any model in particular since I've only done the one conversion :-) I can tell you that fitting it into the w108 was pretty straight forward. Have you had a look at the superturbodiesel forum? Quite a few conversions on there. Hold onto those E300s, lads are starting to realise their worth!

Hi,
There has been activity but it's not the most interesting stuff. Activity at the moment involves attacking small-ish areas of the car one at a time and working through the following process:
1. Blast off all old paint, filler and rust
2. Chop out rust and previous crappy repairs
3. Cut and form patches from new steel
4. Paint and rust proof any accessible bits that aren't going to interfere with welding in the patch.
5. Weld in the new patch
6. Pretty it up by flattening as far as possible so that the minimum amount of filling will be required at painting stage.
7. Eventually the whole repaired car will be blasted and primed before going for painting.

We started on the passenger side and worked around the car front wheel well, sills, rear wheel well, both rear quarter panels, driver's side rear wheel well and sill are pretty much done. Need to clean, protect and then weld up driver's side sill and move on to front wheel arch. A couple of floor patches have gone in too.


Rear wheeel arch/sill repairs:








Driver's side rear sill rust and previous repairs removed.



Another part of the work was to tidy up the area where we welded in the subframe from the E300 W210 car into this one.
Before:


Then it was blasted and painted where possible in the places that were to be covered to try and get some basic protection in there. Wax will also be injected later.


2 large panels were made to cover the front and the back and make it look more like it belongs. Then we dribbled runny paint everywhere to try and get it to run along the seems. I think it turned out great and will look even better when the whole underneath is cleaned and coated.

Bigus wrote: »

At the rate these are going up , you'll be putting it back original and selling it for 35 k 😄

The more desirable the better, Bigus! I hope to have a top class original looking machine that lasts and doesn't break the bank to drive every day. After all this, it'd take a lot to sell it!

Hi Tom. I've no end date. Time is my main enemy, I don't have enough of it. I'd love if I could have all the metalwork done this year. Then paint. Hopefully reassembly won't take more than 6 months. So maybe by the middle of 2018.

Would you believe there's more chopping and welding still going on?! Anyway, I've also been very slowly working on the interior. I'm coming to the end of the work on the door cards so I thought I'd put together all the photos of the process.

My main reason for starting into the door cards at all was because some tool had stuck great big speaker holes in the two front doors as you can see in this photo:



However, when I started to investigate, I found that the original door cards were all disintegrating along the bottom where they were being damaged by water. they had also warped significantly with the damp.




So, I un-picked all the staples that were fixing the covers onto the backing board and removed the vinyl covers.


I then got hold of some stuff called Foamex. It's a foam board (mine is 3mm thick) that has a kind of plastic skin on either side of it. It's a little more flexible than the original door card material but plenty stiff enough with all the fixing points involved. The best part for me is that it doesn't care about moisture so should stay flat forever more! It's intended use is for printing modern signs onto for advertising, exhibitions, etc. I bought mine from a graphics printing place, only about 30 Euro for an 8X4 sheet. I traced around the warped old door cards as best I could and cut out new Foamex versions. I made holes where there should be holes, all done with normal drill bits/hole saws and a Stanley knife. Very easy stuff to work with.



The next step was to stick a sheet of spongy stuff over the Foamex board. I did this because the original "stuffing" if you could call it that seemed pretty tired. It's very weird stuff, a little like a finer version of horse-hair, or the fuzz off a coconut which is bonded to the back of the vinyl door card covers. I figured the sponge would fill things out a little and maybe add to the luxury look once the fittings and stuff go back on. There were some little metal clips had to go on at this point also. They secure the electric window switches for the two rear doors.

I used contact adhesive for everything. Spread it onto both surfaces and wait until it is tacky, then slap the two sides together.
The door card:


The sponge sheet:


And then the two together:



Once that's had a chance to dry, I trim the edges of the foam, clean up the edges of the vinyl cover with a rag and thinners and start to fix it to the new card one side at a time.
Glue on:


And clipped in place:


I've been building in a bit of pre-load into them so that when they are flattened out against the door, they stretch the vinyl a bit. It looks extreme but even warming the vinyl out in the sunshine is enough to allow it to stretch nicely and flatten out the card.





This is a finished one. It needs a bit of a clean but I'm pleased with how they came out:

quietsailor wrote: »

This is probably a really stupid question but here goes anyway - Did you put a different vinyl onto the new backing board? The speaker hole seems to have disappeared

You're right, I should have mentioned that I got a spare set of door cards from a scrap car which were water damaged just like mine but the original vinyl was intact.

Bigus wrote: »

I'd say he's half way through putting the original lV8 petrol back to in to it , before Brexit , because it's worth about £20 k sterling now as an original w108 and diesels have fallen out of favour.

No way Bigus! I'm hard core! I'm sticking it out!! ;-) Sorry for the lack of updates. It is entirely down to a lack of progress! I've been working on a couple of other projects. I've put a Ssangyong 2.9L diesel into a G-wagen which is my current daily driver and I've also been helping out a friend build a competition off-road buggy. Both are pretty-much complete, so I do hope to be getting back at the W108 very soon!