W123 300CD OM603 swap. The Sketchy Coupe *Now with more OM606!*

W123 300CD OM603 swap. The Sketchy Coupe *Now with more OM606!* - Printable Version

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W123 300CD OM603 swap. The Sketchy Coupe *Now with more OM606!* - Granfatherglock - 04-19-2018

Figured I'd introduce myself and my project through this build thread. I'm a Mercedes tech at an indy in Richmond, VA. My younger brothers neighbor was paying someone to tow away his '85 W123 wagon and '83 W123 coupe. He ended up giving them both to me. The Wagon is a whole 'nother story. The Coupe had an OM603 with matching trans sitting in it. It also had the cut springs, factory 16x7 BBS wheels, Zender front bumper, euro rear bumper, and urban camo? hand painted paint job on it when it came under my ownership. I focused on the wagon first and was able to get it running after a lot of work, I now daily drive the wagon. After a while I turned my attention to the Coupe. The previous owner (we'll call him Cap) informed me the engine was in unknown condition and the car was severely rusted, Cap had already replaced the driver side floor pan. My goal here is to build a somewhat enjoyable car for little to no money, as this is a fifth car for me and the condition of the car is, at this point, sub-par at best. Just to be clear, I know this build isn't most peoples taste, but it isn't mine either. We're just working with what we've got!

Here it is after towing it to our shop.
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I first wanted to make sure this was even worth attempting so I ran a ratchet strap across the engine sitting in the bay, rigged up a starter solenoid glow relay, hook up fuel lines, a battery, and hit the starter with some power. Much to the surprise of everyone at the shop, it ran. And it ran pretty damn good. Project Sketchy Coupe is a go.

Progress is constantly sporadic and brief, but I try to have something in the pipeline on this car. After making sure the 603 ran I turn my attention to how to mount the damn thing in the engine bay. I did a little bit of research, and found out my 603 was out of a w126. I decided to attempt to mount the engine using the 126 mounts and spacers. I made spacers out of 3/8" steel plate.

I could only push it so far, and my boys were of no help at all. luckily my brother lives pretty close and came to the rescue.

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3/8" spacer, and I also overbuilt a trans crossmember out of 3/8" as well.

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Time to throw the engine in.

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it pretty much lined up on the first try using w126 om603 arms and mounts with my spacers.

Cap had hacked the radiator top mount/support out in order to shove the engine in to the bay of the sketchy coupe. From what I understand he did this in order to avoid a fine from the city for have an "abandoned vehicle" on his property. This made it a real pain in the ass for me, as the frame rails ended up collapsing in by about 1/2" or so. I was using a 124 603 radiator I pulled out of the junkyard and it wouldn't fit. Rigging up a bottle jack and spreading the rails until my top mount fit again did the trick and I tacked it in place, threw the radiator in, began hacking up radiator hoses until it fit. I'm pretty unhappy with the expansion tank and how that hose is ran. It'll work for now and I was able to bleed it, miraculously.

somewhere in there I did an A/C delete, and the battery was relocated to where the back seat was.

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Bungie corded the grille on for test driving purposes.

I attempted to swap the 126 tach into the 123 cluster in order to have a factory tach.

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This ultimately did not work. the 124 crank signal runs through a few other components that I did not have. I had to figure out another way to get a tach without breaking the bank.

Somewhere along the way I decided to rip out the disgusting interior, and everything behind the dash. Weight reduction bro!

I removed the ALDA, and turned up the pump a couple turns. I also rigged up a w124 om603 throttle cable to the w123 pedal. I ordered some ebay hood pins so I could throw the hood back on. I also cut a big hole in the hood for the exhaust. I drilled a hole at the bottom of the 90° to drain rain and such.

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I wanted to make sure I wasn't melting pistons so I turned to ebay and bought some super reliable chinese gauges. I ordered boost, egt, an a digital frequency counter to attempt to make a tach.

Boost gauge was very easy to setup. After ordering some adapter fitting I was able to install the egt probe into the factory manifold as well. Here I am testing them out:

They work! I can't imagine that egt gauge is incredibly accurate, but hopefully it'll keep me from doing serious damage.

I turned my attention to the frequency counter. I wired it up to a 5V power supply, grounded the ckp, and ran the signal wire to the frequency input pin of the counter. Had to change a few settings around on the counter and it worked! not bad for 8$!

That's pretty much all my progress for the time being. I really need to throw tires, tie rod, clean up wiring, and a battery tie down before I do much else. The plan is welded lower ratio differential, hydro handbrake for skids, and more weight reduction to increase the fun of the car. If I had a higher budget I'd love to do a 5spd swap (we have a few E36 ZF 5 speeds laying around), Turbo, and reworked injection pump. I can't imagine this cylinder head can handle too much more abuse though.

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RE: W123 300CD OM603 swap. The Sketchy Coupe - TKMad - 04-23-2018

Looks like a great project. As long as you're having fun, that's what matters!

RE: W123 300CD OM603 swap. The Sketchy Coupe - Bigpanda16 - 05-17-2018

Looks really cool, I dig it. I have the same cheep egg gauges in three cars, they seem good but I did burn out an led in one and I wish the needle lit up...

RE: W123 300CD OM603 swap. The Sketchy Coupe - Granfatherglock - 07-11-2018

Got my hands on a OM606.962 with matching 722.608 out of a w210 for a few hundred dollars. My plans have changed, I'm now building an OM606 for the sketchy coupe. The plan is a mild 350ish hp. t3 adapter to HX35, intercooler, 4" dp/3" exhaust, 7.5mm elements. The hardest part will be setting the car up to handle the power. I have an E36 LSD diff I could try to shoehorn and get custom axles, I'll also need wider wheels to get the power to the ground and not have a burn out machine.

RE: W123 300CD OM603 swap. The Sketchy Coupe *Now with more OM606!* - Granfatherglock - 07-14-2018

Finally got around to compresion testing my boneyard om606. It didn't go well.

Ended up breaking cylinders 5 and 6 glow plugs. I attempted to extract both without success. So I decided to compresion test 1-4. If they're good I'll keep it and get the machine shop to extract those two glow plugs. If' not I'll bring her back to the scrapyard and keep looking for a good donor.

Well here are my test numbers using the glow plug holes, a spare battery connected to the starter, a battery charger set to 50A on the battery, and a screwdriver to jump the starter. It turned over sooo slow, so I hope that has something to do with the terrible compression numbers. I did not add oil or anything, just screwed my adapter in to the glow plug hole and turned it over.

#1-200psi
#2-220psi
#3-200psi
#4-150psi

I really hate to call this thing toasted, because they're somewhat difficult to get here in the US. This one was dirt cheap, About $300 for the engine and trans. I figure including purchase price, I can rebuild top and bottom end and still not go over $1.5k which is what I'd expect to pay for a wrecked 98-99 w210, or importing a good used engine. I don't have a leak down tester that will fit my glow plug adapter, but I may have to rig something up or at least pull the oil pan and valve cover to see if this thing is even worth salvaging.

Any thoughts, recommendations?

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RE: W123 300CD OM603 swap. The Sketchy Coupe *Now with more OM606!* - atypicalguy - 07-16-2018

Might as well drop the compression and put some stronger rods in it if high hp is on the menu. They usually bend with lots of boost because the native compression ratio is 21:1 or 22:1.

I think you could find a much better motor or a wreck for 1500.

RE: W123 300CD OM603 swap. The Sketchy Coupe *Now with more OM606!* - Granfatherglock - 07-17-2018

I dropped some ATF in cylinders 1-4 and ended up with around 300psi, so I think I'll hang on to it. At the very least it'll be good for parts and mock up. Most running cars are going $2500+ around me, and good used engines are around $2k. I don't doubt with enough patience I could come across a good deal, but this engine was a pretty smoking deal, even if it's less than ideal. Also, I'm not opposed to going through this engine.

I'm not looking to do anything too wild. I don't know much about these since I've been fooling around with my OM617s and the OM603, but I'm hoping for at least 300-350WHP with 7.5mm pump and HX35.

RE: W123 300CD OM603 swap. The Sketchy Coupe *Now with more OM606!* - atypicalguy - 07-18-2018

Yes you will need some elements. You can use the electronic pump on the car, but then you would need an aftermarket controller from Baldur, called a DSL1. You can also use the mechanical pump from the 603 and put some larger elements in. It needs an intercooler. The stock manifold can make that much power.

RE: W123 300CD OM603 swap. The Sketchy Coupe *Now with more OM606!* - Petar - 07-18-2018

I would start it up anyway, see how it behaves. Without 2 glow plugs it'll run rough until warmed up. The pressure might pop the plugs off tho Big Grin

RE: W123 300CD OM603 swap. The Sketchy Coupe *Now with more OM606!* - Granfatherglock - 07-18-2018

(07-18-2018, 05:58 AM)atypicalguy Yes you will need some elements. You can use the electronic pump on the car, but then you would need an aftermarket controller from Baldur, called a DSL1. You can also use the mechanical pump from the 603 and put some larger elements in. It needs an intercooler. The stock manifold can make that much power.

Thanks. Yeah, the basic plan for the build is ever-evolving, but right now my build looks something like this:
-7.5mm OM603 pump
-Factory manifolds for now
-HX35 using a flange adapter
-Keeping an eye out on Craigslist for an intercooler
-722.6 using Ole's controller
-3-4" downpipe and 3" exhaust
-Maybe some A611 valve springs to take us up to 6500-7000rpms?

Like I said, I'm not incredibly familiar with these engines yet, so I do appreciate your insight!

(07-18-2018, 03:15 PM)Petar I would start it up anyway, see how it behaves. Without 2 glow plugs it'll run rough until warmed up. The pressure might pop the plugs off tho

That's not a bad idea! Will have to rig up some sort of cooling system, I would think. I guess I could drop it in the car?

RE: W123 300CD OM603 swap. The Sketchy Coupe *Now with more OM606!* - atypicalguy - 07-18-2018

There is no reason to go chasing the high rpm. Max power is about 5-5500 typically. Then it's time to shift.

Springs are probably not a bad idea although at that power level it doesn't seem like you need much boost.

I went with the 603 pump also but in retrospect erx probably has the right idea with an electronic pump, Ole controller running a larger VNT than stock, and Baldur's stuff for pump control. Then you have a pretty modern-ish setup with excellent drivability.

There isn't a whole lot of room for a big air to air but it would be easy to put some in-line axial flow coolers in and put little water radiators in the wheel wells.

Let me know if you would like to sell the pump from your motor :-)

RE: W123 300CD OM603 swap. The Sketchy Coupe *Now with more OM606!* - Granfatherglock - 07-19-2018

(07-18-2018, 07:28 PM)atypicalguy There is no reason to go chasing the high rpm. Max power is about 5-5500 typically. Then it's time to shift.

Springs are probably not a bad idea although at that power level it doesn't seem like you need much boost.

Interesting, I will still install the stiffer A611 springs, but I guess I'll forgo revving it more than 6k or so. I suppose I'd be choking the engine using the stock manifold at that point anyways.

I went with the 603 pump also but in retrospect erx probably has the right idea with an electronic pump, Ole controller running a larger VNT than stock, and Baldur's stuff for pump control. Then you have a pretty modern-ish setup with excellent drivability.

I didn't grab the engine computer. The module box was wide open, so I'm sure the ME is toast now. My understanding is I can still run a VNT with Ole's controller, e-pump or not. The car is going to be more of a race car. Between HDPE, Auto-x, Rally-x, etc.

There isn't a whole lot of room for a big air to air but it would be easy to put some in-line axial flow coolers in and put little water radiators in the wheel wells.

The W123 has plenty of room, especially with the condenser removed. I have plenty of room for a big AA intercooler in front of the radiator, and smaller trans and oil coolers behind the headlamp housing. With the foglamps removed, I get plenty of airflow..

Let me know if you would like to sell the pump from your motor :-)

I was planning on putting the 6mm elements from it in to another OM603 pump and install the OM603 currently in my coupe in to my daily driver 300TD and selling the current freshly resealed OM617. I'm not opposed to selling the E-pump to fund the 606 build though!

RE: W123 300CD OM603 swap. The Sketchy Coupe *Now with more OM606!* - Granfatherglock - 07-21-2018

Started to tear down the unknown mileage junkyard OM606.
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RE: W123 300CD OM603 swap. The Sketchy Coupe *Now with more OM606!* - Granfatherglock - 08-03-2018

Got the cams and lifters out. Just waiting for my new prechamber socket to come in so I can pull those and swing it over to the machine shop to extract two glow plugs, clean it up, and do any work it may need.

Cams and lifters out

Keeping everything organized in these swanky totes

Fasteners and small parts end up in labeled baggys.

Also, my friend got a 993 3.6 for his '82 911 SC. It came in pieces and he's not quite as organized as I am.

RE: W123 300CD OM603 swap. The Sketchy Coupe *Now with more OM606!* - g wizz - 10-17-2018

pretty sure the elements from the electronic ip can go into the mechanical one. the only other mods you can really do with out going aftermarket elements would be a high volume higher pressure fuel system. want to say 14-28psi? fuel pressure but dont quote me on that. i know 1 bar is safe lol.

RE: W123 300CD OM603 swap. The Sketchy Coupe *Now with more OM606!* - g wizz - 10-17-2018

ha i love this car so much. like just how you know for a fact its pissing off some purist.

did you ever get your tach working? if you use 85 123 stuff it can work cause the 85 motor uses the same mag pick up on the 617 that the 603 uses. so egr computer, gauge cluster, and pick up.

i had mine working till i fried stuff by hooking up a battery backwards... tarded i know..

RE: W123 300CD OM603 swap. *Now for sale* - Granfatherglock - 10-29-2018

This car is now for sale.