OM616 on a test stand - PeachParts Mercedes-Benz Forum

d!0+]@9$f3>yEI$Il3ZQ · #1 08-26-2021, 11:33 AM

So I bought a 616.916 with manual transmission, I've never owned anything like this before so there are lots of new things to become familiar with. I intend to use it in something like a Model A speedster but I'm still looking for a chassis to start with. In the meantime I want to get the engine running well.

It came from a W115 that was being swapped to a 2JZ, owner said he drove it for a while with the 616 and always wanted to swap it. So when the starter failed he pulled the whole thing out and started the swap rather than fixing it. I have not tested the starter to confirm.

I built a test stand for the motor, just waiting for motor mounts to arrive so I can finish it up.

I've been looking over everything and I was hoping you guys could help answer some questions I'm having a hard time with, since I never had a whole car some things are just unclear when looking at this.

1. Where does the valve cover breather tube connect to? On some pictures I've seen it goes to the fitting on the bottom side of the intake manifold, but there is no where for it to go on mine and I don't have the tube itself.

2. What are the bolts on the intake runners for?

d!0+]@9$f3>yEI$Il3ZQ · #2 08-26-2021, 11:41 AM

3. What size bolts should fit into the front of the head? I normally work on Japanese stuff so I have a big bucket of random fasteners and nothing fits. Is the German stuff a different thread pitch? Or do you think the threads in the head may be messed up? How many bolts should the water pump have? I see some extra holes that don't have bolts in them.

4. Where should the vacuum lines be plumbed to from the vacuum pump? One goes from the intake manifold to pull fresh air? And the other? I assume some sort of vacuum manifold would have been used to distribute vacuum to multiple places in the car? Can I send this directly to a brake booster if I use power brakes? If I don't use power brakes I assume I can just remove the vacuum pump altogether?

5. How is the fuel cutoff arm operated? Pull back/up? What is that rubber mount for? Can I get rid of the mount?

d!0+]@9$f3>yEI$Il3ZQ · #3 08-26-2021, 11:48 AM

6. Can I block off the heater core water outlets on the side of the head and water pump if I'm not running a heater?

7. Are 3 points of support enough for engine and transmission? I see some other brackets on the bottom of the engine and transmission but the only mounts I found for sale were 2 on the engine and the one on the tail of the transmission. Just want to make sure I'm not missing anything I need.

8. Is it common to have part numbers starting with 615 on parts on the 616 engine? I assume these are just leftover from the previous OM615 in the W115, and when Mercedes changed over to the 616 they didn't need to change any of those parts. Or do you think this 616 engine was swapped into this car at some point?

9. Does this engine have 2 water temp sensors? I see one at the thermostat housing, at one on the side of the head?

d!0+]@9$f3>yEI$Il3ZQ · #4 08-26-2021, 11:53 AM

10. Do the throttle arm pivots look bent to you? Or are they supposed to be like that?

11. Do I need the throttle butterflies in the intake? Could I remove them and use just a single arm from my throttle pedal to the injection pump? I've seen some other cars without them and I'd much prefer not to have all those pivots and rods running everywhere.

Anything else you can see on here that I should know? My plan is to do the bare minimum to make it run just to make sure it's worth working on, then I'll do all the maintenance on it, oil change, fuel filters, valve adjust, tstat, etc...

d!0+]@9$f3>yEI$Il3ZQ · #5 08-26-2021, 11:54 AM

Wow, that turned out to be a lot. I had to split it up due to the photo limit. Let me know if you guys want to see anything else.

resago2000 · #6 08-26-2021, 12:24 PM

you have a vacuum operated pump, do not remove the butterfly valve or the pipe running from the throttle to the pump.
the rod connected to the pump is only the idle damper, and can be removed if you want, just helps smooth low idle

heater pipe nipples can be removed AFAIK

the engine gasses where just piped into the intake before the butterfly assembly. can also be vented to outside if you dont care about certain things

water sensors, the one in the head is temp, the one on the coolant neck is a switch the triggers the aux fan

the vacuum pump, vacuum is on the port currently without the hose, the vacuum pump expels air in to the intake.
you dont really need a vacuum pump in the case, personally, I would get a block off cover and use an electric setup, just my opinion though

the large bolt bosses on the front are where the huge AC bracket would attach

gmog220d · #7 08-27-2021, 08:29 PM

Quote:

Originally Posted by d!0+]@9$f3>yEI$Il3ZQ

8. Is it common to have part numbers starting with 615 on parts on the 616 engine? I assume these are just leftover from the previous OM615 in the W115, and when Mercedes changed over to the 616 they didn't need to change any of those parts. Or do you think this 616 engine was swapped into this car at some point?

The OM616.916 2.4 uses the same manifolds and most of the accessories as the OM615 2.2 that was in the 220D. I swapped an OM616.916 2.4 long block into the '73 220D without any hassle. Everything fit and worked. One difference I know of is that the alternator setup changed between '73 220D and '74 240D. The valve covers are different, too.

One thing you should check is if the governor system holds a vacuum. If it doesn't the injection pump will deliver too much fuel.

d!0+]@9$f3>yEI$Il3ZQ · #8 08-27-2021, 11:10 PM

Quote:

Originally Posted by resago2000

7) 3 is enough, sometime there is a damper on the bottom of the rear of the engine that hooks in to the trans mount, but not many have that I think
8) yes, the 616 was used in the 115 and 116, the intake varied a little. so the numbers are fine

first link in my sig has lots of pics of the same engine you have

Great, thanks I will check out those pics.

Quote:

Originally Posted by resago2000

actually, since you have a manual, the butterfly is the only thing you are concerned with as far as throttle, just about connection point should work.
you could get rid of all the rods and turnbuckles and just control throttle with a cable on the butterfly valve.

Quote:

Originally Posted by gmog220d

I'll second this.

With the rod that runs over the top of the engine removed you lose the fast idle option for when starting the engine cold. In the car there's a little knob on the dash that, when rotated, pulls a cable that runs to the bracket that's mounted to the valve cover. That cable then holds the throttle linkage open a bit, upping the idle speed. You can always use your foot instead!

Quote:

Originally Posted by gmog220d

The OM616.916 2.4 uses the same manifolds and most of the accessories as the OM615 2.2 that was in the 220D. I swapped an OM616.916 2.4 long block into the '73 220D without any hassle. Everything fit and worked. One difference I know of is that the alternator setup changed between '73 220D and '74 240D. The valve covers are different, too.

One thing you should check is if the governor system holds a vacuum. If it doesn't the injection pump will deliver too much fuel.

Ok, I was getting a bit confused with this stuff so I just made a quick video...

http://www.youtube.com/watch?v=gA8G9mFesOU

gmog220d · #9 08-28-2021, 11:36 AM

Some comments on the video:

- The lever on the back of the injection pump has nothing to do with fuel output control. All it does, when the throttle is at idle, is push a spring-loaded vibration damper against the fuel rack to smooth idle out. You can remove the control rod that runs to the lever, and let the lever stay down under spring tension, without causing any problems.

- Yes, the governor uses vacuum to limit fuel delivery. Think about towards the end of the video where you are looking into the throttle body at the little venturi that's dedicated to the governor. When the throttle plate is closed more air will be sucked through that little venturi thus creating more vacuum. As you open the throttle less of the intake air will go through the little venturi, thus reducing the amount of vacuum created.

The vacuum signal created in the throttle body acts on a spring-loaded diaphragm inside the injection pump. That diaphragm is connected to the fuel rack. The coiled spring pushes the diaphragm and rack forward to increase fuel output, while the vacuum acts on the diaphragm to pull it and the rack back to limit fuel output.

At idle, while max vacuum is created, the rack is held back to limit fuel output so the engine runs at idle speed. Opening the throttle all the way reduces the vacuum to a minimum, which allows the coil spring to push the diaphragm and fuel rack forward thus delivering max fuel output.

If you remove the throttle plate from the throttle body there will be little-to-no vacuum to hold fuel delivery back and the engine could runaway uncontrolled.

- It does appear that you have the later style glow plugs. You are correct that all you need is 12V to that last plug to power them up. The original system was all manual control, and provided a visual aid for determining how long to glow, in the form of a resistor strip in the dash that glows with the plugs. There was no relay to control the cycle.

- RE testing for vacuum leaks - Yes, pull a vacuum on that line and see if it holds. There are two main causes of leaks in the system; bad diaphragm, and worn and leaky "adjusting shaft" and its bushings (this is the shaft that's controlled by that rod that comes down to the lever from above). A leak could be caused by one or the other, or a combination of the two. A less likely cause of vacuum leak would be a cracked housing.

This thread should shed some light on what's happening inside the back of the pump:
Parts for Pneumatic Governor, OM615 and OM616

- Yes on straightening out the bent lever at the throttle body. You are correct that the one is supposed to move the other.

- So yeah, you can remove both rods that run from the throttle body to the injection pump with no ill effects. When you remove the one that runs down to the lever on the injection pump you're making it so the rack damper stays forward all the time. When you remove the top rod you then lose your idle speed controller. All basic throttle related functions are still intact at this point.

gmog220d · #10 08-27-2021, 09:46 AM

Quote:

Originally Posted by d!0+]@9$f3>yEI$Il3ZQ

5. How is the fuel cutoff arm operated? Pull back/up? What is that rubber mount for? Can I get rid of the mount?
Attachment 163080 Attachment 163081

The lever is operated by a cable that runs up to the dashboard, attached to the so-called "gorilla knob" that is used to start and stop the engine. The knob controls whether or not the injection pump will deliver fuel (stop and run), and also engages the starter when pulled all the way back. The rubber block is where the cable sheath connects to the injection pump. Pushed all the way forward the lever on the pump is in "stop" position. The default position is "run". Pulled back puts it in the "start" position.

You could possibly remove the rubber block, but you'll still need some arrangement for controlling the position of the lever. In the car the lever is held forward in the "stop" position by the cable. When disconnected from the cable the lever will default to the "run" position.

PS - Nice looking shop!

d!0+]@9$f3>yEI$Il3ZQ · #11 08-27-2021, 10:43 AM

Quote:

Originally Posted by gmog220d

The lever is operated by a cable that runs up to the dashboard, attached to the so-called "gorilla knob" that is used to start and stop the engine. The knob controls whether or not the injection pump will deliver fuel (stop and run), and also engages the starter when pulled all the way back. The rubber block is where the cable sheath connects to the injection pump. Pushed all the way forward the lever on the pump is in "stop" position. The default position is "run". Pulled back puts it in the "start" position.

You could possibly remove the rubber block, but you'll still need some arrangement for controlling the position of the lever. In the car the lever is held forward in the "stop" position by the cable. When disconnected from the cable the lever will default to the "run" position.

PS - Nice looking shop!

Ok so is this labelling correct then?

I'm having a hard time imagining the operation of the cable, you say that the cable holds it forward to the stop position by default? So you must pull the cable in the car to start the car? So the car starts with a cable and not with a key?

Does the "start" position on the pump modify fuel delivery at all during startup?

resago2000 · #12 08-27-2021, 12:25 PM

with the fuel shutoff, anything other than stop is run.
2 choices only

gmog220d · #13 08-27-2021, 07:53 PM

Quote:

Originally Posted by d!0+]@9$f3>yEI$Il3ZQ

Ok so is this labelling correct then?
Attachment 163105

Yes. And as resago2000 pointed out there is nothing else going on inside the injection pump while the run/stop lever is pulled into the start position.

I got curious about that, as I coulda swore I read years ago that when in the start position the rack inside the injection pump is pushed forward to increase fuel delivery during starting. But nope it ain't so. I couldn't find it in the manuals. I took a used pump off the shelf and removed the side plate so I could see the rack and elements while operating the run/stop lever. Pulling the lever back does nothing to the rack.

Quote:

Originally Posted by d!0+]@9$f3>yEI$Il3ZQ

I'm having a hard time imagining the operation of the cable, you say that the cable holds it forward to the stop position by default? So you must pull the cable in the car to start the car? So the car starts with a cable and not with a key?

The gorrilla knob has four positions:
- Stop (all the way in)
- Run
- Glow
- Start (all the way out)

When released after starting, the knob/cable will default to run. To stop the engine push the cable forward into the dash.

The key turns on the electrics, and unlocks the steering.

resago2000 · #14 08-26-2021, 03:13 PM

referring to #2, pull out one of those bolts and see if they are banjo bots, if so, you are missing the pipe that you've seen on other cars.

gmog220d · #15 08-27-2021, 08:57 AM

Quote:

Originally Posted by d!0+]@9$f3>yEI$Il3ZQ

1. Where does the valve cover breather tube connect to? On some pictures I've seen it goes to the fitting on the bottom side of the intake manifold, but there is no where for it to go on mine and I don't have the tube itself.
Attachment 163074 Attachment 163075

2. What are the bolts on the intake runners for?
Attachment 163076

You're missing some bits and pieces of crank case breather system. See this thread for answers to these two questions:
Oil Bath Air Filter Filling with Oil

If you still have questions let us know.