230SL R11 Injection Pump Lever Return Resistance

[Tomnistuff]

Back on July 8, While in the midst of completing my restoration and preparing for Meeting of the Clans II, I reported that,  among several other things, my Injection Pump Arm had a tendancy to hang up at about half throttle unless an extra return spring was added to the linkage.

I added the extra spring and went on with my business of getting ready for my trip to London, Ontario and Dan’s Benz Barn in Port Lambton, Ontario for my long weekend with many of you.

Since I’ve been home from that incredibly enjoyable experience, I’ve been trying to make perfect some of the things that demonstrated their less than perfect behavoir during the trip.

One of my pet peeves has always been stiff throttle pedals.  That extra spring I added to the linkage to bring the injection pump lever consistently back to the closed throttle stop, appropriately damped of course, is not something I could ignore on a thousand kilometer trip taking 13 hours going and 15 hours coming back.  My limp was probably noticeable to some of you.

Along with LF brake squeal,  alternator/water pump belt  squeal, rich idle stalling at about 150o C during warmup, a driver’s window that dropped about a half inch after hitting a pot-hole and parking lot steering like a tractor, I have begun to reconsider the effect of the Injection Pump Lever Stiffness on throttle efforts and driving comfort or lack thereof.

Can someone please pop their hood and take a look at his or her injection pump return spring to see if it appears somewhat misinstalled or cocked at an angle like mine in the first photo below?

Also, would someone be so kind as to pop off the upper socket of the throttle linkage where it attaches to the injection pump rod, open the injection pump lever fully open, then slowly and gently release it back toward closed throttle to see if it closes all the way to the stop smoothly or does it tend toward hanging up at some open throttle position, as mine does in the center photo of the three pump lever photos.

Thanks for any advice you can provide.

Tom Kizer

[Charles 230SL]

Can someone please pop their hood and take a look at his or her injection pump return spring to see if it appears somewhat misinstalled or cocked at an angle like mine in the first photo below?

hi Tom, attached is a picture of the return spring on my R11 pump in the closed-throttle position. The spring appears cocked to some extent just like yours is, and I think this is normal. I noticed my pump doesn't have a 'cap' covering the return-spring. Any chance that cap could be binding or impeding movement of your throttle lever?
 

Also, would someone be so kind as to pop off the upper socket of the throttle linkage where it attaches to the injection pump rod, open the injection pump lever fully open, then slowly and gently release it back toward closed throttle to see if it closes all the way to the stop smoothly or does it tend toward hanging up at some open throttle position, as mine does in the center photo of the three pump lever photos..

Tom, I did as you requested and I noticed my throttle lever does tend to hang up around the 1/2 closed throttle position - it certainly doesn't bind but it does hesitate slightly while returning back to the fully closed position. I think this normal, and the slight hesitation is certainly overcome by springs elsewhere in the throttle linkage.
I remember several years back that my accelerator pedal was slow to return to the closed position, causing the throttle to remain slightly open - but this was easily remedied by replacing the spring on the firewall (pic below).

[Tomnistuff]

Charles, thank you very much for your photos and comments.  I noticed that, in addition to the cap that mine has and yours doesn't have, the springs terminate at a different points on the lever.  If they "anchor" at the same point on the IP housing, yours has about 180 degrees more or less wrap than mine does.
In the first of my three "full lever" photos, the one at full throttle, if you blow it up, you can barely see the hook on the end of the spring where it wraps over upper edge of the lever left of and below the shaft.  On yours, the hook terminates on the lower edge of the lever to the right of and above the shaft.  I went into the garage and verified mine.

You may very well be right that my spring is binding inside the cap.  I noticed that when mine binds at about half throttle, the spring "shifts" its position when I touch the lever to trigger its release and return to the stop.

Before I disassemble it to explore, I need to ask if there is a "positive", idiot-proof assembly relationship between the lever and the shaft.  I'm reluctant to remove the lever if I cannot be sure I can put back in the exact same place on the shaft.

During my restoration, I made a big mistake with the driveshaft balance by taking it apart without marking the mating positions of the two halves, so I learned my lesson.

Do you know the answer about the lever and shaft?

Tom Kizer

[mnahon]

Hi Tom,

Can you PM me your email address and I will send you a document on how that lever comes out of the pump---it's attached from inside the pump. It's not simple, and as you say, doing it without taking precautions could throw off your pump. Pat (shvegel) had helped me with this and I kept a record of our discussion. In my case, I was changing the lever on a FIP because the lever had broken.

Also: I tend to doubt you could do this with the pump still on the engine---you'd have to remove it from the engine first.

Meyer

[Benz Dr.]

The position of the shaft is critical and should never be played with. Also, don't ever start the engine or turn it over with the shaft removed!!! It will bend stuff inside of the pump that you may not be able to fix, or worse ruin your pump.

A certain amount of resistance upon return seems to be quite common and as long as there isn't any gritty feel to it you should be OK.

[Charles 230SL]

..I need to ask if there is a "positive", idiot-proof assembly relationship between the lever and the shaft.  I'm reluctant to remove the lever if I cannot be sure I can put back in the exact same place on the shaft.

hi Tom, I know of no idiot-proof relationship between the lever and the shaft - the orientation of the throttle lever on the shaft is calibrated with the pump off the engine. As Dr. Dan stated, the position of the shaft is critical. You may have already seen this: https://www.sl113.org/wiki/Fuel/Injection - but it provides a great explanation of how the throttle lever affects internal works of the pump.  Note that the shaft is connected to a lever inside the pump that rotates a cam - a stylus 'reads' the cam and adjusts the rack. If you loosen the throttle lever and permit it's orientation on the shaft to change, you'll change/rotate the position of the cam and likely (mal)adjust the rack. I know of no way to correctly re-orient the throttle lever on the shaft without removing the pump.  respectfully, charles

[Tomnistuff]

Thanks everyone for your comments, opinions and especially warnings.  Apparently my driveshaft lesson (separating the halves without marking their alignment) was well justified.  By the way, I got lucky when I reassembled it.  I could not have gotten lucky with the IP.

I'll just have to fine tune the throttle efforts without "violating" the IP, and live with the results.

Thanks, also, Meyer, for the pump lever write-up.

Tom Kizer