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  #1  
Old 02-24-2015, 09:50 AM
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M120 engine...a learning experience

So Ive be fascinated with the Mercedes V12 M120 engine. Mainly because it was used in the Pagani. Ive been messing with cars since I was 14 but never rebuilt an engine or anything. So yesterday I went to the junkyard and picked a M120 out of a 92 600SEL. It has 117,xxx miles on it. It was sold as "parts only". So basically a core. I paid $250 for it. My plan is to see if I can get it to run on a stand, controlled by a stand alone ECU (megasquirt most likely). Ive never done this before so I decided to go with one of the hardest options out there to learn from. So heres the engine. I brought it to the garage and went to my job. After work stopped by and decided to see what I bought. Took the sparkplugs out and poured some oil into the cylinders (engine was sitting on the shelf for 5 years). Then i turned it over by hand, and it turns over pretty easily. I want to simplify the engine by removing anything unnecessary to it, like the EGR valves and make it run by cable instead of wire throttle bodies. Any help and advice will be greatly appreciated.

Now to the pictures:






Plugs looks like ran a little rich


Some green crystals on two of them... i think antifreeze=blown head gasket
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  #2  
Old 02-24-2015, 07:12 PM
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Always fun to get a new project.

These motors are 2 M104 6 cylinder heads put on a V12 block. The M104 is only known for leaking oil at the front of the head and not coolant.

From the plugs, the motor was running super rich. Firing plugs will burn off antifreeze so the source of the green is a bit id a toss up, might even be from engine removal where they stuffed a heater hose in the intake.

The fastest way to test for combustion to coolant leak is put the piston at top with both valves closed and pump compressed air into the spark plug hole then look for bubbles in the coolant. In your case you will need to add water ( freeze hazard this time of year ) or seal all coolant ports then cover the last one with a rubber glove / balloon or similar. Be sure the piston is at top, it the crank is slightly off air will rotate the motor.

This is also called a leak down test, you will get some leakage out the exhaust and into the crankcase. Air coming from the intake is possible due to length of time it has sat and carbon flaking off parts.

Once you get the combustion to coolant issue tested, pull the oil pan and inspect connecting rod bearings. If you pass these two tests, the motor should run with a fuel system. ( I'm assuming that the timing chain is still turning the cams )
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  #3  
Old 02-24-2015, 09:07 PM
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Thanks for the advice! I ordered a starter today so I want to due a compression test and then do a leak down test. My guess for the running rich is the wiring harrness breaking down and causing faulse MAF readings (seen a guy on youtube have that problem).

Where can I find diagrams for all the vacuum lines? I want to see what I need to keep and what to remove.

Also I looked online and could find a Oil filter relocation kit. Anyone done it?

Thank you
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  #4  
Old 02-25-2015, 12:40 AM
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Quote:
Originally Posted by ruski View Post
Thanks for the advice! I ordered a starter today so I want to due a compression test and then do a leak down test. My guess for the running rich is the wiring harrness breaking down and causing faulse MAF readings (seen a guy on youtube have that problem).

Where can I find diagrams for all the vacuum lines? I want to see what I need to keep and what to remove.

Also I looked online and could find a Oil filter relocation kit. Anyone done it?

Thank you
I don't think anyone has done a relocation on a 120, or if they have they haven't really posted about it. The aftermarket for all of Mercedes is eye openingly tiny, and that's doubly so for a low production, expensive motor like the 120.

I'd have to see what the oil filter pattern is to see if any of the solutions from the smaller motors would work, but unfortunately my suspicion is that they will not.

As far as vacuum lines I'd try and find a W140 service manual as I cant find one online. Otherwise I'd seek out Roncallo, a member here who swapped a 120 into an R107 SL so he knows as much/more on the motor as anyone here.
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  #5  
Old 04-06-2015, 02:16 AM
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Kuddos for doing something with this unfairly ignored engine!

What is it going into?
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  #6  
Old 05-09-2015, 04:15 PM
88Black560SL
 
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Wow

This ought to be interesting getting one of these engines running on a stand. Years ago that is exactly what I was planning on doing if I couldn't get my engine to run with the factory ECUs.

Essentially the M120 is 2 six cylinder engines and uses a separate ECU for each side. Since I had COP and wanted to stay with COP my approach at the time was to use two MS units just like MB did. The challenge may have been synchronizing the two and how to control idle. Could I make 1 ECU in charge of Idle for both sides.

Your car uses distributors and may be able to do a 12 cylinder wasted spark setup. I know you could if you had one 12 cylinder distributor like the old Lamborghinis but you have 2 6 cylinder distributors. I leave it to you to figure out how to separated the two.

But who knows last time I was on the MS sight a new unit was about to be introduced but never did get released. Maybe the new MS systems accommodate 12 cylinders a little more graciously.

A good throttle body to use for this engine to get rid of the throttle by wire would be a 70mm 5.0 Mustang throttle body.

Good luck with this and keep us up to date.
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  #7  
Old 05-09-2015, 09:34 PM
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Quote:
Originally Posted by Roncallo View Post
But who knows last time I was on the MS sight a new unit was about to be introduced but never did get released. Maybe the new MS systems accommodate 12 cylinders a little more graciously.
FWIW, MS3x has 8 logic coil drivers and 8 injector drives and can control a V12 in wasted spark/batch fire or in full sequential/wasted spark if you're creative with your outputs. It does a bunch of other cool stuff but to answer your question it does V12 at least a little more gracefully than the old MS2/e.
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  #8  
Old 05-10-2015, 03:04 PM
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For what its worth, I don't think that's coolant/blown head gasket on your plugs. Most likely its corrosive salts formed during combustion that have reacted to moisture in the air/intake/engine to form those crystals you see. I have worked on and changed a lot of blown head gaskets and cracked heads having worked on cars for a living most my life. And on almost all of them, the spark plugs are clean and the ceramic around the electrode is white because the water in the coolant flashes to steam and blasts the carbon off. The cylinder burning coolant is usually very clean. Your plugs are nice and black with carbon. I think you are safe as far as that goes. You can do a variety of checks to make sure without tearing into it. Close the cooling system and pressurize with air. Perform a leakdown check. Not only can you possibly see if air is getting into the cooling system but it will give you a cylinder health check. Also, drain the oil off and check for water. Wouldn't hurt to verify the cam timing is correct too. Looks like fun though. It would be neat to do a twin turbo build on one and drop it into an unassuming lookin Benz! Twin turbo V-12 Ponton sleeper? W123-W124? W201? Lots of possibilities!
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Skippy~ As for perception: Drive what you like and can afford. Those who don't like it can supply vacuum to one of your components. LOL

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  #9  
Old 12-05-2015, 04:26 PM
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So this project has been sitting on the back burner, until now. So I placed a few orders for this project and got the car that this engine is going into. Here is everything I got so far:

-MS3Pro with wiring harness
-GM Open Element IAT Sensor
-GM Closed Element CLT / IAT Sensor
-Hall effect crankshaft position sensor
-GM 3 Bar MAP Sensor
-8 1/4" 36-1 Trigger Wheel
-2x Q45 90mm cable throttle bodies

Need to order-
-O2 sensors- Still havent decided wideband or not and what brand- suggestions?

The engine is currently has two distributors. Should I buy seperate coils or COPs? Am I missing anything else?

Im planning on moving the throttle bodies forward and also redesigning the oil pan to make it as slim as possible or maybe try dry-sump but dont really want to go that route. Got three quotes for custom equal length headers: $5000, $4800, and $4000 for the set. For that price I would be better off going turbo.
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  #10  
Old 12-07-2015, 06:14 PM
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Thanks for the updates.

For headers, I'd be real tempted to look at off the shelf V6 parts that have close port spacing then make your own flanges. I "think" the flanges are the same as a M104 inline 6 and someone from the turbo side of things probably has a set.

Have a look here for a recent aftermarket FI build.

http://www.peachparts.com/shopforum/performance-paddock/368301-560sel-m117-megasquirt.html
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  #11  
Old 12-07-2015, 06:17 PM
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Also, be sure to pull the oil pan and have a look at the rod and main bearings as those are the main reason for an engine failure regardless of brand.
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  #12  
Old 12-10-2015, 11:21 PM
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Quote:
Originally Posted by 97 SL320 View Post
Also, be sure to pull the oil pan and have a look at the rod and main bearings as those are the main reason for an engine failure regardless of brand.
The oil pan will coming off to be redesigned any ways.

Does any one have a diagram and dimensions of the bellhousing?
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