Early 250sl injection pump rebuild

[Magruder]

Ok this is my first appearance on the site.
I recently bought an early 67 250 sl. At first thought I had an oil leak but after reading allot on this site I have come to understand the the injection pump is the issue. Having learned that there are two different pumps I believe I have the early one. It has the orange oil fill/ breather cap and a dip stick. Can someone verify that assumption?
The unit is filling to over fill and leaking out cap. Being the older unit I understand that the oil reservoir is self contained, not feed from motor. From my research that is telling that this is a leaking seal allowing fuel to contaminate the oil I.e. the leak. Please confirm.
The functioning of the pump is fine, car runs great. That being the case is there any reason I cannot get a seal kit, replace all seals and reassemble not having to send pump off to be completely rebuilt. If so is there a good diagram out there to assist in the process?

[mauro12]

I recently rebuilt the injection pump in my early 250sl . I don’t have the 250sl pump but a pump from a 280 ( calibrated for the 250).
From my experience is not convenient to touch these pumps unless you are aware of what you do . The best option for me was to send it to Germany and have it overhauled professionally . The fuel contamination in the engine oil is so typical of these cars . It depends from the calibration , delivery valves or injectors . Let them touch only by professionals.

[thelews]

The first thing I would do is make sure the oil is filled to the proper level on the DIPSTICK (separate from the filler cap) for the injection pump.  If too high you'll need to suck some out. 

[dirkbalter]

I don't think the later pumps 250+ have actual dipsticks. Its just a cap. But you can certainly poor a bit of oil in for initial lubrication. The 280 pumps (mine at least) don't have any access for oil filling or verification.

[BobH]

Ok this is my first appearance on the site.
I recently bought an early 67 250 sl. At first thought I had an oil leak but after reading allot on this site I have come to understand the the injection pump is the issue. Having learned that there are two different pumps I believe I have the early one. It has the orange oil fill/ breather cap and a dip stick. Can someone verify that assumption?
The unit is filling to over fill and leaking out cap. Being the older unit I understand that the oil reservoir is self contained, not feed from motor. From my research that is telling that this is a leaking seal allowing fuel to contaminate the oil I.e. the leak. Please confirm.
The functioning of the pump is fine, car runs great. That being the case is there any reason I cannot get a seal kit, replace all seals and reassemble not having to send pump off to be completely rebuilt. If so is there a good diagram out there to assist in the process?

Have a look on here, everything you need to know

https://www.sl113.org/forums/index.php?topic=4199.0

[Magruder]

Appreciate the info. This pump was bleeding oil out the cap, thin oil.
I have managed to suck out all the bad stuff, know there’s a fun exercise!!
Ended up putting 200mls back in that brought it to full on dip, may not have gotten all, believe 300 is the number.
That said let’s go drive this puppy.
Sold my 280 15 years ago for $20k thought I did well, times they are a changing!! Missed it ever since. Hoping my collect is back to complete.
Thanks for the input, I’ll be back

[BobH]

There's a picture on here, seems sometimes the T bar may not be there, so it may be just a screw

https://www.sl113.org/forums/index.php?topic=17027.msg117441#msg117441

[dirkbalter]

Bob, deleted my question, felt stupid. Found it.
Thank you

[BobH]

I thought i'd dreamt it!

[rwmastel]

Having learned that there are two different pumps I believe I have the early one. It has the orange oil fill/ breather cap and a dip stick. Can someone verify that assumption?

Let's deal with facts and clear up the assumption.  What does the metal Bosch ID tag say on the side of the pump?  You can post a pic if you want to type less.  :-)

[rwmastel]

That being the case is there any reason I cannot get a seal kit, replace all seals and reassemble not having to send pump off to be completely rebuilt.

I don't know everything about these pumps, not by a long shot, but I agree that the pump should be professionally rebuilt instead of anything done at home.  If you've been reading the Injection Pump threads, then you've probably read that the extremely tight tolerance of the fuel plungers in their cylinders is actually what prevents the oil from mixing with the fuel.  I don't think a "seal kit" exists.  If you want to get a spare pump to tear down on your work bench and learn how they work, some are for sale right now in our For Sale forum.

When I got my late 66 230SL, the pump was overfull.  Pulled the dip stick and lots of oil came out and made a puddle on the garage floor.  Removed and replaced the oil to proper level, drove the car a lot for a couple months, removed and replaced the oil to proper level again (it was much less overfull second time), another couple months driving, and the oil level checked OK.  It seemed it just needed exercised to decrease the problem.  Have others experienced this after buying their w113 with early pump?

[Ed Riefstahl]

Hey Rodd,

I have a 66 230sl purchased 21 years and 65,000 miles ago. I did the top end shortly after purchase and a lot of servicing. Just this past week I changed the oil in the injection pump for the first time. The level was right where it should be on the stick. It was a little dirty color, but not really all that bad considering.

I siphoned it out with a mighty vac and a pc. of plastic vacuum tube used on later MB's. I poured the oil into a measuring jar to measure qty. and look for foreign material. I filled a hand held pump type oil can with straight 30 weight oil and used the same tube to put new oil back in. Very quick and easy as it turns out.

I've never touched the IP and guess I never felt a need to do anything to it. Is there something I should be doing to the IP due to the age and miles since purchase?

We are considering another road trip this summer if I can get the noise figured out, possibly a month and up to 5000 miles. I'll admit, I'm getting cold feet a little after this recent noise has shown up out of nowhere. It's really making me nervous.

Just wondering if I should be thinking of doing something proactive to avoid sudden failure, considering how far from home we drive our car.

Ed Riefstahl
1966 230SL (Ms Magoo)
1970 280S (Miss Daisy)
1989 300SE (Majestic)
1999 BMW Z3 5 speed
1991 BMW 318I 5 Speed
1997 Toyota Paseo Convertible - Red 5 speed (have you ever seen one?)
1997 Ford Ranger step side (Mater)
2023 Mazda CX 5

[rwmastel]

Other than watching the oil level, I'm not aware of any regular "maintenance" on the IP.  Well, maybe check that its air filter is clean/functional.  If it constricts air flow, then sometimes people do other adjustments to compensate instead of just replacing the air filter, which just makes more of a mess of the system.

[BlackForest]

There is a lot of incorrect or partially correct info on this site regarding injection pumps prior to the 280SL.
I will do my best to clarify some of the ongoing concerns using the 250SL injection pump as an example.
All 250SL pumps have a separate oil circuit for lubricating the internal moving parts.
It is the same oil circuit in the front of the pump (pump housing) and rear of the pump (governor housing).
The oil migrates from the governor housing through the rear camshaft bearing into the pump housing.

The oil line that is attached to the pump from the motor is to create oil pressure for what Bosch refers to as oil blocking.
It also serves the purpose of lubricating the lower half of the plunger.
The oil block prevents the fuel from the upper half of the plunger leaking to the lower half and ultimately into the internal pump lubricating oil. The principal being that the oil pressure is higher than the fuel pressure thus blocking the fuel from leaking and migrating down the plunger.

The actual oil blocking o-rings are a seal between the barrel of the plunger and the pump housing.
There is one for each plunger and barrel element. They serve to keep the oil pressure in a small gallery at the top of the pump housing. When they fail, the oil then drains into the pump lubricating circuit, thus overfilling and leaking out of the fill cap.

Why do some pumps fill up with this leaked oil quicker than others?
1-2 o-rings leaking vs. all of them. (Over time they will all leak about the same)

Why do some pumps have a stronger gas smell in the oil than others?
This is due to the loss of oil blocking and the overall condition of the plunger and barrel elements.
It also has to do with how gasoline diluted the engine oil was in the first place.

In any event the cause of the failure is the same, failure and leaking of the o-rings in the barrel seats.

For the above concern for Magruder, the easiest thing to do is simply remove the dipstick and let the oil drain out.
Then reinstall the dipstick (some more oil will ooze out) and drive the car a few miles.
Park the car and remove the dipstick.
No oil comes out? Reinstall dipstick and drive 10-20 miles and recheck.
This will allow you to determine how bad the o-ring leakage is.
If it turns out to be minimal and a rebuild is not in the budget, then suck out the oil completely and fill with fresh.

I would set the oil level a little low, as it will overfill regardless.
The oil level is set by placing the dipstick in the recess only, NOT screwing it in.

Photo attached of an R18Z I just completed testing and calibrating.
This one had completely failed o-rings and the oil would spew out at idle.

[dirkbalter]

Excellent. Very helpful.
Thank you very much.

[thelews]

I've seen Michael in action with these pumps, like a surgical room.  He tests and calibrates them on a period tester, just like they did when new.   Very impressive machine, BIG!

[Alex D]

Black Forest rebuilt my early 250sl injection pump back in 2017, runs perfect no problems took a awhile but well worth it.

[Benz Dr.]

There is a lot of incorrect or partially correct info on this site regarding injection pumps prior to the 280SL.
I will do my best to clarify some of the ongoing concerns using the 250SL injection pump as an example.
All 250SL pumps have a separate oil circuit for lubricating the internal moving parts.
It is the same oil circuit in the front of the pump (pump housing) and rear of the pump (governor housing).
The oil migrates from the governor housing through the rear camshaft bearing into the pump housing.

The oil line that is attached to the pump from the motor is to create oil pressure for what Bosch refers to as oil blocking.
It also serves the purpose of lubricating the lower half of the plunger.
The oil block prevents the fuel from the upper half of the plunger leaking to the lower half and ultimately into the internal pump lubricating oil. The principal being that the oil pressure is higher than the fuel pressure thus blocking the fuel from leaking and migrating down the plunger.

The actual oil blocking o-rings are a seal between the barrel of the plunger and the pump housing.
There is one for each plunger and barrel element. They serve to keep the oil pressure in a small gallery at the top of the pump housing. When they fail, the oil then drains into the pump lubricating circuit, thus overfilling and leaking out of the fill cap.

Why do some pumps fill up with this leaked oil quicker than others?
1-2 o-rings leaking vs. all of them. (Over time they will all leak about the same)

Why do some pumps have a stronger gas smell in the oil than others?
This is due to the loss of oil blocking and the overall condition of the plunger and barrel elements.
It also has to do with how gasoline diluted the engine oil was in the first place.

In any event the cause of the failure is the same, failure and leaking of the o-rings in the barrel seats.

For the above concern for Magruder, the easiest thing to do is simply remove the dipstick and let the oil drain out.
Then reinstall the dipstick (some more oil will ooze out) and drive the car a few miles.
Park the car and remove the dipstick.
No oil comes out? Reinstall dipstick and drive 10-20 miles and recheck.
This will allow you to determine how bad the o-ring leakage is.
If it turns out to be minimal and a rebuild is not in the budget, then suck out the oil completely and fill with fresh.

I would set the oil level a little low, as it will overfill regardless.
The oil level is set by placing the dipstick in the recess only, NOT screwing it in.

Photo attached of an R18Z I just completed testing and calibrating.
This one had completely failed o-rings and the oil would spew out at idle.

Just one question. If you check oil level with the dip stick sitting in the tube, not screwed in, wouldn't it show as over filled when checking later on when it is screwed in?

[thelews]

Just one question. If you check oil level with the dip stick sitting in the tube, not screwed in, wouldn't it show as over filled when checking later on when it is screwed in?

Yes, just like my riding lawnmower.  When I check the oil level I need to unscrew and wipe the dipstick first and then reinsert but not screw down.

[BlackForest]

Ha John, I don't think the Bosch engineers of the late 50's would appreciate you comparing their high-tech work with your lawnmower!

[MikeSimon]

Yes, just like my riding lawnmower.  When I check the oil level I need to unscrew and wipe the dipstick first and then reinsert but not screw down.

Lot of motorcycles require that procedure.

[thelews]

Ha John, I don't think the Bosch engineers of the late 50's would appreciate you comparing their high-tech work with your lawnmower!

Kawasaki was right up there with Bosch!

[BlackForest]

Regarding Dan's inquiry:

Yes, of course if you check the oil level incorrectly by screwing in the dipstick it will read overfilled.
But more importantly, if you set the oil level (incorrectly) by first screwing down the dipstick, you will be setting it considerably under full.

On these early pumps (R11 and R18) the lubricating oil level is approx at the center line of the camshaft.
It needs to be high enough so the oil can migrate through the rear camshaft bearing and into the pump housing.
Looking back at previous posts on this topic, I don't think this has ever been understood or explained. Some thought the oil pressure line for oil blocking was lubricating the lower pump housing, but that is incorrect. -Except when the seals are leaking of course!

The photo below shows where the oil level would be on an R18/R18Z pump with the dipstick NOT screwed down.

[BlackForest]

Lot of motorcycles require that procedure.

I have 2 early 70's BMW motorcycles and the motor oil level is checked exactly the same way (not screwing in the dipstick).
The recess makes it easy to set the dipstick in to a consistent level and simply pull out to check.
I have seen plenty of pumps with an incorrect or missing dipstick seal. This variable would cause inconsistency in checking the level. The correct seal for the dipstick is a fiber seal.