OVERFLOW VALVE REPLACEMENT early 1980s DIESELS
 

I don't know if this is the only way to post this, but Mercedes does supply the overflow valve on the back side of the injection pump. I have seen repeated entries about stretching the internal spring to 27mm. After 35 years these springs wilt, and should probably be replaced.


The problem in going to the dealer and in looking at epc net online parts is that my pump shows no overflow valve, but the pump that preceeded it shows the part. I ordered this part not knowing whether it included the inner spring and ball bearing or if it would even work. BOTH MERCEDES PARTS AND EPC NET SAID THIS VALVE WAS NOT FOR MY CAR. I also admit naivety, but had I given this number on the old part to the parts department, it would have made this easier. The parts guy also did not suggest getting the part number off the valve, and did not look for it.


I have not installed the valve yet, but I called a local company that rebuilds the old IPs, and they told me this new part number is a direct replacement for what I have. If you have an overflow valve and a clear fuel line on the back of the IP, this part should fit.


The old part number is imprinted on the 17mm "nut" and it is 14174 over 13012. The direct replacement for this part, according to the rebuilder is 14714 over 13046 which is what I received from Mercedes for $23.37 net. A brillo pad should hopefully reveal the part number on your valve. I have included a photo of the old and new valves. According to the rebuilder, the ball bearing on the end of the valve does nothing but to seal the assembly. Everything critical seems identical.


FUNOLA, if you are still watching, Mercedes does not carry the smaller silver washers at this connection or the 14mm bolt on the fuel filter, but they now send a copper compression washer, WHICH MAY BE A PROBLEM. I was told that Mercedes used other washers than silver, but found that they had a metal reaction fusing the parts together which would be a big problem on the side of the IP and the head on the large filter. I am guessing that the problem is not at the brass-ended fuel lines but on the injection pump and large filter head. Using copper on either may cause you to replace or pull those two parts to fix the problem.

I have been a member of this forum and spent a lot of time looking at other mercedes forums. I have never read of any one having an issue using a copper washer on the Filter Bolt.

The copper washer can some times be used by reheating them red hot and letting them cool.

Copper or aluminum washers both should be fine. Is the valve on the left with the exposed ball the new one? I'm curious how that can work w/o fuel leaking out of there.

I went with Greazzer's performance overflow spring. Worked great. IIRC it cost less than the quoted MBZ price as well.

NEW INFORMATION
 

For some reason, I cannot open my attachment (too large a file?).


Yes, the new version is on the left, and it is a sealed unit, according to the MB parts guy. Note that the new part does not have the cap that holds the spring and ball bearing in place. When you read the manual, many pumps have a relief valve, so that when you prime them, they will let any air (fuel?) out. If it is not sealed mechanically, you have a large bearing at the end, with the spring pushing both bearings apart. It could be the four times greater mass of this outer bearing keeps it from leaking. Remember, the small inner bearing will only give way when there is enough pressure, and when that happens, the fuel will flow through the hole on the side of the valve into the clear line. I will let you know the results when I hopefully get the engine started


I am still suspicious of the copper washers interacting with the IP (which looks like steel) and the filter housing, which could be aluminum. I know that connecting a heavy copper fitting to steel pipe will not be a problem for a long time, but connecting steel to thin copper pipe can be a problem, and these copper washers are thin, about 1 mm. I have seen this when I re-plumbed my boiler and many of the pipes which were copper, steel and cast iron.


With regard to geazzers spring, I think it was for a 300D turbo, and never found out if he had one for a 240D.


I am getting a quote on some aluminum washers, and will relay the results. All of my washers are original and they are all silver on all three of the clear lines. When I bought the clear line that goes to the fuel pump body (where the primer pump is), there was a note on a tag to use silver washers.


BTW, THE PART NUMBER THAT I GAVE FOR THE VALVE IS A BOSCH NUMBER. THE NUMBER FOR MERCEDES SHOULD BE A 000 074 72 84. I am assuming that this part will work on any pump with a clear fuel line to the BACKSIDE of the IP. And, as I said, I will put up the results.

MORE INFO & UPDATED PHOTOS
 

The new valve is on top in each photo.


I tried to push the ball bearing on the new valve in and it doesn't move. Since the spring is small, it should be easy to do. I therefore believe that the large bearing on the end is stationary and sealed, somehow.


The only difference that I see is that the hole on the new valve is slightly smaller.

I was selling all 4 flavors for the OM616 / OM617 family of engines:

Turbo Spring
Non-Turbo Spring

NEW Turbo OFV
Rebuilt Non-Turbo OFV

IMAGE OF BAG THE VALVE CAME IN, on request
 

If you use epc.net, and enter model 123123, North American, and click on the valve, it will say it does not fit this car. It is the same for the clear lines, also.

DOUBLE DARN
 

Well, I got it all together, it started up in 3 tries and subsequent starts are easily; but the engine is running so rough that it will not even hold an idle; also making a lot of noise; no smoke; no fuel leaks.


I replaced all of the return lines; the clear lines off the IP; the primer pump and the new overflow valve.


The car sat 7 months, but I think the fuel is OK, and looks clear in the filter.


For now, I am going back to the manual to see what tests I can do related to the lift pump that the primer pump is mounted.


Ay, caramba!

Might take a bit to bleed all the air from the system, and it will indeed sound like hell and run badly until then. It may not even be running on all cylinders yet. Do you have a clear piece of tubing on the fuel return, to check for air bubbles?

How's the rest of the engine? When were valves adjusted, glow plugs in good order?

LOTSA BUBBLES
 

I started the car again, and I am getting a solid stream of bubbles coming through the clear fuel line running from the overflow valve on the back of the IP to the large filter. Is that the return line you are asking about?


I don't get this as I have probably run the engine for 15 minutes total. Yesterday, I also pumped the primer pump for between 5 and 10 minutes. It filled the clear fuel line mentioned above, and then some. I never heard any noise from the overflow valve while priming, as Funola suggested.

The overflow valve you have operates on a different principle than the original 2-piece valve did. The old-style valves had a spring and a ball inside and kept a constant pressure in the fuel system. The new-style valves have a drilled orifice and a weak spring holding closed a non-return valve. The orifice is smaller to provide restriction. Either valve should work if your lift pump is in healthy shape. The new-style valve showed up with the M pump and was standard equipment on the OM60x series engines.

If you have air in the system, find the leak, likely your primer handle if its the old style. The OFV won't have anything to do with air in the system. Since there isn't a ball bearing chattering in the new style OFV, you won't hear it "squeak" when priming.

LIFT PUMP GUMMED UP?
 

Diseasel300, I have read many posts where you need to stretch the spring to 27mm for good performance in the old valve. My spring was 20.5mm long. The new spring is thinner and shorter but the valve seems to operate on the same principle as the old valve. Both versions have a ball bearing first (the valve)in the path followed by the spring which logically should be calibrated to maintain a certain static pressure of fuel delivery to the IP. While a Bosch repair company says this new valve is the direct replacement for the valve I have, it stands to reason that if it opened at a lesser pressure, things won't be good.


I replaced the primer pump with a new Monarch pump. I closed this firmly after priming the system. How do you test the lift pump when the engine is not running? Do you know what causes these lift pumps to fail and at how many miles? I am at 156,000 miles.

Actually on my year and model the mimimum presure si 8 psi at idle and 18 psi at 3000 rpm. So the valve does not hold a specific static pressure all though the rpm range.
No specifics on it but at 3000 rpms there is less time for the elements to fill so the higher pressure compenseates for the reduced fill time.