Injection Pump - only some of the pistons are moving... how to free the others?

[scoot]

Here's a 250SL injection pump.  I'm trying to get all of the pistons to move when I rotate the camshaft by hand.  What happens is that 3 of the pistons and springs move as expected and 3 don't.  On the ones that don't, I can push the piston down (based on position of cam shaft) but when I do so the spring doesn't decompress, then when I rotate the cam shaft again the pistons move back up and stay there unless I manually move them down.

How do I free whatever is stuck?

thanks
Scott

[ja17]

Keep using the same procedure with plenty of penetrating oil and/or alcohol. In addition move the rack to different position during the procedure. The cylinder bores around the pistons may move upward if you turn the pump with the fittings off. The cylinder bores are "keyed" in their critical keyed position. If they move up then turn, they can get out of critical keyed position. If this happens, carefully turn them back to the keyed position and then back down.  Be careful not to move the rack if any cylinder bores have moved up out of place. The rack can safely be moved if all the cylinder bores are in place. Keep tapping the pistons down as needed, with a hard wood dowel.  Occasionally move the rack when all cylinder bores are keyed and  down in place. Then repeat the procedure of tapping the pistons down. The stuck pistons will not allow the rack to move or will make the rack hard to move.  Once all pistons are free, the rack will only then move freely and return to its rest position after being moved.

Take your time, do not damage the pistons using hard metal to tap them down (use hard wood) or aluminum. Clearances in the bore are in millionths of an inch. They do not tolerate much abuse.

[scoot]

Keep using the same procedure with plenty of penetrating oil and/or alcohol. In addition move the rack to different position during the procedure. The cylinder bores around the pistons may move upward if you turn the pump with the fittings off. The cylinder bores are "keyed" in their critical keyed position. If they move up then turn, they can get out of critical keyed position. If this happens, carefully turn them back to the keyed position and then back down.

Thanks for the reply Joe.  I don't know if what I've done is making the situation better or worse.   I removed the fittings on the top of the pump on the offending pipes.   See attached picture.  It was not possible for me to remove just the 19mm fitting without getting the one below also.  Inside the fittings there is a spring.  The other piece shown in the picture goes into the pump.  So I took that out.   Then I tapped on inside of the place where those piece where with a long punch and one of the "stuck" things gave way and started moving up and down as I turned the pump. 

  Be careful not to move the rack if any cylinder bores have moved up out of place. The rack can safely be moved if all the cylinder bores are in place. Keep tapping the pistons down as needed, with a hard wood dowel.  Occasionally move the rack when all cylinder bores are keyed and  down in place. Then repeat the procedure of tapping the pistons down. The stuck pistons will not allow the rack to move or will make the rack hard to move.  Once all pistons are free, the rack will only then move freely and return to its rest position after being moved.

Unfortunately my vocabulary is sorely lacking.  I have looked and kind find a picture of what is meant by "the rack" although I have done a lot of reading and looking.  The pistons in my first picture can move freely up and down but whatever is going inside the big springs doesn't move independent of the piston.  In this context, is "piston" the part that looks like a piston as seen from the side with the cover off below the big springs?  Movement of that piston seems to have no bearing on getting the spring to decompress, however tapping from above with the fitting and key removed does seem to free things up. 

Have I done it all wrong?
thanks
Scott

[scoot]

I guess I need a simple definition of
Piston
Cylinder Bore
and Rack.
...

:-(
Scott

[sandcrab59]

I have great success with Marvel Mystery Oil. Put it in the cylinders and let it soak for a couple of days.
Keep trying and eventually they will free up.
Could take a week or so.
This is of course if you did not damage any moving parts inside.
Tom

[scoot]

Put it in the cylinders and...

OK, so to add to my list of words I don't know in this context:

1.  cylinders
2.  piston
3.  rack
4.  cylinder bore

I don't know which parts are meant by the above terms.
help?
thanks
Scott

[sandcrab59]

Scoot:
I will try and explain these terms to you.
Joe (JA17) can verify.
A- Think of an engine, staring at the bottom.
B- at the bottom there is a crankshaft which turns as your engine runs.
C- Attached to the crank is the rods which has the pistons attached to them.
D- The pistons run up and down in a cylinder which is bored out in the engine block.
E- As these pistons go up and down they fire and make the engine run and also exhaust the fumes.
F- This of course is what is in the block without the cylinder head.

Now as my memory remembers (I have diesel engines and I have a good book that explains how the injection pump works, I have had this book since the 70's. It is a navy manual).
I Just pulled the manual out (1976) and try to explain.
A- At the bottom of the Injection pump (IP) there is a cam shaft  just like the crankshaft shaft in an engine.
B-On top of this camshaft are lifters with springs sitting on top of them. Just like lifters in a head of an engine.
C-On top of each spring is a gear with teeth.
D- these gears rotate because alongside them is the rack. This rack is a long rod with matching teeth that runs from the back of the IP to the front of the IP.
E-On top of the rack is the fuel oil sump (Gas) . This is where the gas enter the IP.
F- Passing thru this sump are barrels for each injector.

Here is where it gets difficult to explain what happens to the gas to reach the injectors.
G-As the camshaft turns it pushes  springs up and down which rotates  the gears which pushes the rack, left to right or right to left.
H-The rack rotates the barrels (one at a time) in the fuel sump pump .
I- the fuel lines to the IP are under low pressure and places fuel into the fuel sump pump.
J- The barrel is hollow inside with an opening  to gather a small amount of fuel and then rotates upwards and it closes off the opening so it does not collect anymore fuel.
K- As the barrel reaches it upmost travel it rotates and the opening places the fuel into the injector fuel line under extremely high pressure.
L- When fuel is delivered the barrel rotes downwards and when it reaches the fuel sump pump it is ready to collect the next shot of fuel.
M- These barrels are in cylinders just like pistons in a engine.

Using the term fuel is because I am use to diesels. Fuel in the above means gas.
You know the term , a picture is worth a thousand words, I am looking at the naval manual with the page that has a detail drawing of the IP.
All I did above was interpret the drawing .

Hope this answers you question about terms.
Tom



















L-
E-

[ja17]

Good explanation Tom,

Yes these mechanical injection pumps are derived by the first MB diesel production automobile in 1926!

Scoot, it is ok that you removed the check valves under the 19mm fittings. The check valves are the spring and cone valve.  Beneath the check valves are the piston (sometimes called the plunger) and the bore or cylinder where the piston moves up and down. Don't worry about the springs below for now. The rack is the horizontal gear rod which moves front to back in the injection pump. Look in the injection pump tour for some good pictures of the rack and IP internals. The rack moves front to back in the IP, rotating the pistons and changing the fuel quantity injected depending on many factors such as linkage position, barometric pressure, engine rpms and engine temperature. Dirty fuel and water left for long periods of inactivity, will cause rust or varnish to accumulate in the bores of the injection pump, causing the pistons to stick. Since the pistons are tied in to the rack, the rack is held from moving by the stuck piston. You can remove the small circular cover on the front end of the IP and gently move the rack by tapping it if is stuck. Removing the rear cover on the IP will allow you to move the rack forward again. Once the rack is free, it will move freely and return to a "rest position". This will not happen until all the pistons move freely. As previously mentioned, move the rack then work on the pistons and repeat the process.

It may be too late to save this IP if you have been tapping the pistons down with a hard metal punch. Slight deformation of the pistons will never allow them to move freely again. Hopefully you have not had to tap hard enough to damage anything. Switch to  a hardwood tool or aluminum to prevent damage.

[scoot]

Thanks to both of you for taking the time to reply.

Scoot, it is ok that you removed the check valves under the 19mm fittings. The check valves are the spring and cone valve.  Beneath the check valves are the piston (sometimes called the plunger) and the bore or cylinder where the piston moves up and down.

So when I have removed the check valve including the spring, and the small thing with 4 splines as shown in my photo (cone valve?), what I see is a hallow tube (the bore or cylinder).  If I place a thin object into the bore and rotate the pump on a working cylinder the thin object moves up and down, the big spring on the side panel expands and contracts, and the shiny thing (that looks like a piston) beneath the big spring moves up and down.

What I did was place a long metal punch through what I am thinking is the bore and tap on it and POOF it gives way.  After that rotating the pump causes that cylinder to do the stuff that the working ones does.    Was that wrong?  It wouldn't have budged with something soft and honestly I don't know what is strong enough yet soft enough to fit inside the cylinder to the piston...

Don't worry about the springs below for now. The rack is the horizontal gear rod which moves front to back in the injection pump. Look in the injection pump tour for some good pictures of the rack and IP internals.

I'm assuming you mean the section in the Technical Manual called Fuel Injection located here:  http://www.sl113.org/wiki/Fuel/Injection

The rack moves front to back in the IP, rotating the pistons and changing the fuel quantity injected depending on many factors such as linkage position, barometric pressure, engine rpms and engine temperature. Dirty fuel and water left for long periods of inactivity, will cause rust or varnish to accumulate in the bores of the injection pump, causing the pistons to stick. Since the pistons are tied in to the rack, the rack is held from moving by the stuck piston. You can remove the small circular cover on the front end of the IP and gently move the rack by tapping it if is stuck. Removing the rear cover on the IP will allow you to move the rack forward again. Once the rack is free, it will move freely and return to a "rest position". This will not happen until all the pistons move freely. As previously mentioned, move the rack then work on the pistons and repeat the process.

This confuses me.  It sounds like you are saying that if you have ANY stuck pistons the rack won't move, and the result is no fuel (cleaner) gets pumped to the lines.   I have a pump with some stuck pistons and some free pistons which to me implies the rack shouldn't be moving and therefore I shouldn't be getting fuel out of any of the lines.  Yet I am out of half of the lines.  (Explanation of my test method follows)

Test explanation - I have two pumps with the same symptoms.  One is connected to a car, one is on my kitchen counter.  The one connected to the car is a 6-plunger M189 pump and I have a fuel pump circulating a mixture of 80% carb cleaner and 20% ATF through the injection pump (bypassing the rest of the fuel system).  While doing this I have small injection pump lines with baggies on the ends of them to collect anything that comes out of the pump.  If I crank the engine, I get the cleaner mixture out of some of the lines.     

On my kitchen counter I have a similar injection pump from a 250 SL/SE.  This is a "dry test" except for spray lubrication and spray carb cleaner.  The 250 pump is a core on which I am experimenting.  If it "works" on the 250 pump I repeat on the M189 pump. 

It may be too late to save this IP if you have been tapping the pistons down with a hard metal punch. Slight deformation of the pistons will never allow them to move freely again. Hopefully you have not had to tap hard enough to damage anything. Switch to  a hardwood tool or aluminum to prevent damage.

Again this makes me wonder if the place I am inserting the long very thin tap into (under the check valve and cone valve) a cylinder until it rests on something.  Is that the "piston" that it is resting on?

One more question...   When all of the pistons move up and down, do I need to free the rack as you describe IF I have fuel/cleaner coming out of the lines when I crank the engine?

And finally, The electric fuel pump I purchased for this purpose fried (melted?) after a few hours of use, probably because the cleaning mixture wasn't gasoline.  Can anyone recommend a reasonable priced pump that I can use for the purpose of circulating cleaners other than gasoline through various parts of the fuel system that I wish to clean?

thanks
Scott

[Bonnyboy]

Scoot,  not wanting to delay all of your efforts so far but I would suggest that you get an alternate injection pump (a cheap one) that you can take apart and bash about to learn how it works.  I'm with you on trying to understand what all the names are???   To end my confusion I bought a pump out of a sedan, and took it partially apart and put it together again and then took it apart at a club meeting and the number of light bulbs that went on over the member's heads was outstanding. 

These pumps are robust to do what they are supposed to do but I expect that trying to force anything can have devastating results.   

I have since shined it up and put it on my bookshelf in the garage as decoration.  I probably pulled it down 10 times to see how things worked and have had a couple members come over to see how it worked before they tried something on their own car.   For me the Pagoda is just another toy in my garage that I play with much like I play with my other toys - I like to know how things work.    Gonna take apart a FREE twin cylinder aircompressor next week to see if I can make it work.   

[scoot]

Scoot,  not wanting to delay all of your efforts so far but I would suggest that you get an alternate injection pump (a cheap one) that you can take apart and bash about to learn how it works. 

Hi Ian -

Actually I am doing that sort of.  My "real" project is a rare 6 cylinder pump in a car with an M189 engine.  It most closely matches the 250SE/SL pump that I have on my kitchen counter.  Probably I should take the 250 pump apart further.  What I have done so far is try it on the 250 pump and if it works then apply the result to the M189 pump.

I think that you are right - I should take the 250 pump apart further.

thanks
Scott

[Naj ✝︎]

Hi, Scoot,

Hope you know some German  

I believe the M189 pump is R19?

[ja17]

Scoot, yes you are tapping on the top of the pistons (not shown on Naj's illustration, but inside #10). Check the level of the bores #10 on Naj's  illustration (Thank's Naj ! ). Even if the rack is stuck, some piston which are moving will pump fuel. Stuck pistons will not. The rack will remain stuck or hard to move until all pistons are moving feely.

[ja17]

Scoot here is some more information.  In these photos the bores are labeled  "cylinders"..................

[scoot]

Hope you know some German  

I know enough German to understand 75% of commercials, the traffic report, and the weather report on the German radio stations I listen to.  (75% because they are so context sensitive and repetitive).   I get maybe 25% of the news.   With written German it is easier because I can go slow and use Google Translate as needed.   If I have to speak it it comes out all mush with occasional English and Russian words thrown in by mistake.   

The diagram is helpful, thank you for posting it.

[scoot]

Scoot, yes you are tapping on the top of the pistons (not shown on Naj's illustration, but inside #10). Check the level of the bores #10 on Naj's  illustration (Thank's Naj ! ). Even if the rack is stuck, some piston which are moving will pump fuel. Stuck pistons will not. The rack will remain stuck or hard to move until all pistons are moving freely.

And would I be correct in assuming that the rack is part #27 in the illustration?

[scoot]

Scoot here is some more information.  In these photos the bores are labeled  "cylinders"..................

Thank you Joe.  I understand better.   I am thinking from what I have digested that I want to try to wiggle the rack with an M4 screw - trying to move it back and forth a little, is that correct?  Do I do this from the front only or from the front and from the back?   I can get an arbitrarily long M4 screw FWIW. 

[ja17]

Yes 27 is the rack and the threaded hole is in the front.

[Kevkeller]

Whatever happened with this Scott?

I’m experiencing the same symptoms. Did you get the pump working again?

Kevin

[Benz Dr.]

I'm not trying to rain on anyone's parade here but I've said this before so I'll say it again.  None of us have the ability to rebuild these pumps. It takes a lot of time to learn everything you need to know about them, a build sheet to make all of the correct adjustments, and test equipment to make it work right. To that end, if you just want to fool around with an old pump to see what's inside I can't see a problem with that. If you want to do external adjustments that's something that you should know about. If you're planning on starting a pump rebuilding business then you will need to learn everything about them.

 My concern here is only that we might inadvertently confuse someone into thinking they can rebuild their own IP and have them end up with a lot of damaged parts. I've had people hand me a box of parts from a IP they took apart wanting me to fix it for them. The only thing that saved this pump was they numbered all of the injection elements. Pump rebuilder was NOT impressed.

So, there are some things you can do yourself and others where you should be wise enough not to touch.

[Kevkeller]

I certainly don’t plan on rebuilding mine or taking it apart. My engine hasn’t been run in over a year because of other maintenance I was trying to get done. I finally went to restart it tonight and it wouldn’t start. I determined that only the rear 3 cylinders were getting fuel (I cracked the injector line nuts) and they eventually did fire.  The front 3 remained dry. It could be that the injector pipes are clogged and I will check that next time. 

I am assuming from what I have read here that my injector plungers are stuck.  It doesn’t sound too difficult to unfreeze them by removing the check valves and tapping them with a hard wood or brass. The pump is still in the car and if this is a viable procedure I will try it. Unless it’s not recommended. This will most likely be the extent of my trouble shooting. I don’t mind too much sending it out but would rather not if possible.

I used to work on diesels and I know that the injector pumps and injectors were built to extremely high tolerances, probably to millionths. I don’t know but I’d find it hard to believe these were built to those same tolerances as I doubt they’d need that precision and it would be a waste of money. I’m usually wrong though.

I was curious if Scott was successful. Thanks for your advice though.

[mbzse]

.../...I used to work on diesels and I know that the injector pumps and injectors were built to extremely high tolerances

They most certainly were. As JoeA writes the tolerance for the plunger in the pump cylinder is 2 microns, and the slightest surface corrosion (or scratches) will ruin your pump's performance. A bit like watchmaking technology. The injection pumps are assembled submerged in a bath to avoid dirt or dust particles when factory or professional workshops do this. I'd say, it is not a device a layman can easily work with on the kitchen table...

Also, as DanC pointed out, one needs a series of jigs and measurements to assemble and adjust the basic settings in these pumps, long before they are mounted onto an engine.

.../...hard to believe these were built to those same tolerances as I doubt they’d need that precision

The Bosch fuel injection pumps for our old Mercedes definitely need and have that degree of precision, just to the same level as the diesel units you worked with

[Kevkeller]

Like I said, “I’m usually wrong.” 

Not arguing,just discussing, but diesel pressures are much higher and need very tight tolerances to achieve those pressures. I was also taught that with the tight tolerances you needed the lubrication properties of diesel fuel. If you ever used gas in a diesel injector it would seize.

I just find it surprising that they’d need such tight tolerances for much lower pressures that gas engines deal with.

But the cleanliness, jigs, time, knowledge, etc would definitely preclude me from taking one of these apart.