Delivery valve internal leak as a cause of nailing? Yes? No? Maybe??? - Page 7 - PeachParts Mercedes-Benz Forum

dieselbenz1 · #91 04-27-2017, 11:00 PM

Do you use a pick to snag them out I seem to recall them being flush with the crush washer? When I had a pump in for servicing years ago they said they adjusted the registers and explained it as setting the pop pressures of the delivery valves. I never read anywhere if this is even possible.

Diseasel300 · #92 04-27-2017, 11:05 PM

Yes they can be lifted out with a pick, toothpick, or a magnet. The new one can simply be dropped in.

Not sure what they did, but there isn't really a "pop pressure" for the DV. The spring just keeps the valve closed. There's no shim and no adjustment of the DV itself. As long as the pumping element is pushing fuel, it will flow through the DV. Perhaps they set the pop pressure of your injectors? If not, they may have been blowing smoke up your backside...

dieselbenz1 · #93 04-28-2017, 09:49 AM

Well I know they never touched my injectors as I only had given them my IP. They had run the IP on the machine adjusted things and made a point of saying now all the registers have been set. I now guess that is referring to the metered amount of fuel passing through the DV's?

Diseasel300 · #94 04-28-2017, 10:36 AM

It sounds like they were adjusting the fuel metering. I'm surprised they did this, most places I called when I had IP issues said they wouldn't adjust a used pump, it had to be rebuilt before it was allowed on their machine. I understand their reasoning, even though I don't like the consequence.

dieselbenz1 · #95 04-28-2017, 11:07 AM

Hmmm this is even stranger now I was also told the pump had a slight non repeatable hesitation when returning to idle but that would require a rebuild and big bucks so I accepted it and never had any issues with it. I was never certain what they did but it had cost 600 about 10 years ago.

Father Of Giants · #96 04-28-2017, 09:17 PM

Great research in this thread. Learned a lot! I will conduct my own research as well by replacing the delivery valve washers and o-rings on my injection pump and see if that stops the nailing from my injectors as well.

Will also use Shell diesel and see how that goes.

I should report back in this discussion no later than mid march and see how everything ties together.

Diseasel300 · #97 04-28-2017, 10:40 PM

Quote:

Originally Posted by Maxbumpo

Can you post some pix showing the DV wear? I beginning to think that is my issue as well, with new Monark nozzles and now worse performance (worse smoke, steady nailing from #3 cylinder). If a visual inspection can confirm the DV is the issue, I'll be more confident about pulling that DV.

Bear with me, camera operation is NOT my forte. I borrowed a better camera today and took some pictures of the DV out of #4 and the DV out of #6. For whatever reason, #4 was camerashy and didn't want to turn out a good image. #6 is clear as a bell.

The photos attached to this post show the moving plunger of the DV and the stationary "ring" part, which is what your sealing washers are actually sealing against. Note that the plunger part of the DV's are upside down in the photos. The part that looks like a fat phillips screwdriver fits down inside the stationary "barrel".

The beveled face of the stationary "ring" is in decent shape on both DV's. The wear is to the moving plunger part on both DV's that were problematic.

#4 actually has pitting on the wear ring, however since the camera decided it didn't need to turn out a focused image (this is the best one out of TWENTY FOUR attempts), this is the best we get.

#6 came out very sharp. Irritating that the very first image I took of it turned out perfect. The red arrow points to the wear ring (black ring) all the way around the plunger part of the DV. You can actually feel it with your finger nail if you scrape over it. The DV that replaced it does not have this wear ring and it is not nailing.

I hope this helps the "visual" crowd, even though the blurry picture of #4's DV can make your eyes bleed if you look at it long enough. The beveled face of the plunger part of the DV shouldn't have a wear ring on it. If you have nailing and your DV plunger has pits or wear on the sealing face, replace it. It would be interesting to know what caused the wear, that's an answer I don't have.

Maxbumpo · #98 05-11-2017, 01:28 PM

Yesterday my new copper washers and o-rings arrived, so I swapped out the #3 delivery valve for one from an old (dead) injection pump.

The bottom side of the delivery valve had some residue on it, so I polished that off on a rag and took a picture of the wear (at the twelve o'clock area of the DV face).

The "new" delivery valve makes a world of difference, all the nailing is gone now. Idle is still a little rough, but smoking is far less.

Diseasel300 · #99 05-11-2017, 07:39 PM

Sounds like yours is in the same boat mine's in. Idle still a bit rough from time to time (comes and goes) but miles ahead of what it was. Certainly no more "dead miss" feeling. Mine hasn't nailed since the DV's got redone. I have nearly 800 miles on the car since the last DV swap and it only seems to run better the more it's driven.

RunningTooHot · #**100** 05-13-2017, 01:37 AM

Wow guys! I'm really glad to see how this all came together since my initial posting. Take a bow everyone, great job! Especially you Diseasel!

One question, although the answer seems relatively obvious. Has anyone determined with absolute certainty as to whether the central plunger of the delivery valve assembly is uniquely matched with the outer cylinder piece? It would seem that with such precise tolerances and that chamfered face, mixing & matching inner & outer pieces probably isn't a good idea.

But that is theory... what has your practical experience been?

I'd be concerned that the cylinder-to-cylinder fueling balance would be off when arbitrarily putting in pieces from a used pump. But then again, it's pretty damn "off" when that plunger isn't sealing! So slightly off is better than hellaciously off...

Diseasel300 · #**101** 05-13-2017, 09:16 AM

According to everything I've read or been able to find, the DV's are a matched set. The plunger and the barrel are machined to give a good tight seal. Since BOTH of the DV's I've replaced have shown wear to both the plunger face AND to the matching chamfered face in the barrel, I wouldn't waste my time just replacing the plunger. You'll still have problems, if not immediately then at some point sooner rather than later.

The DV's will NOT affect anything to do with fuelling calibration. They're nothing more than a check (non-return) valve. Their pressure is determined by the spring in the DV holder. A worn and leaking DV will certainly affect fuelling calibration since it can leak back and that line will have a different initial pressure than the other lines in the system.

RunningTooHot · #**102** 05-13-2017, 11:22 AM

Thanks! That makes perfect sense. When looking at a cross-section of a pump, it's more evident that they serve simply as a check valve to maintain residual pressure in the hard lines. With the bleed down of a defective valve, the delivery volume is reduced, and the timing would be delayed significantly.

Now it's a matter of sourcing. I'm curious what they'd cost new from a pump shop versus cannibalizing an old pump.

If they are prohibitively expensive, I've got another idea. How many people here are old enough to have ever used valve-grinding paste? (For hand-lapping cylinder head valves.) I'm wondering if that could possibly suffice to clean up the mating surfaces?

Diseasel300 · #**103** 05-13-2017, 11:28 AM

No idea about the cost of new valves, I haven't looked. I had a spare IP to harvest parts from and those valves were fine, so that's what I used.

I too have thought about attempting to lap the valves, but haven't done anything with that yet. Providing there isn't any excessive pitting, I'd be inclined to think that re-lapping the valves should provide satisfactory results. At some point I may attempt a re-lap of one of the damaged valves to see if there is any sort of improvement.

RunningTooHot · #**104** 05-13-2017, 11:53 AM

Quote:

Originally Posted by Diseasel300

...I too have thought about attempting to lap the valves, but haven't done anything with that yet. Providing there isn't any excessive pitting, I'd be inclined to think that re-lapping the valves should provide satisfactory results. At some point I may attempt a re-lap of one of the damaged valves to see if there is any sort of improvement.

That would be a very cool experiment to try. It may be a bit of a challenge to keep the paste from going inside the bore and possibly messing with the clearance between the center pin & bore... which I now discovered is highly critical too.

I did some research, and what I found was both logical, yet counter-intuitive. Seems the DV's not only hold the line pressure, but they are designed to slightly reduce the line pressure before holding it. (!) This allows the injector to snap shut cleanly to avoid any dribble or secondary burn. From the description, it appears to be a hydrodynamic effect. The nuanced engineering that goes into these old "simple" mechanical pumps is amazing.

Check it out: Bosch Injection Pump Delivery Valves | Diesel Engine Troubleshooting

barry12345 · #**105** 05-13-2017, 11:58 AM

I have never seen a metal to metal check valve last forever. The valves in these injection pumps seem to last a long time though.

They are busy check valves as well. Weak return springs may cause then to wear quicker as well. If they do not get back on their seats quick enough flow erosion may be more probably. They may be a matched pair of parts but I doubt it. Machines for a long time now can generate perfectly flat surfaces. So I doubt they are lapped as a pair.

I can see lapping on the injector element cylinder and piston.

Rebuilt injection pumps now are pretty expensive. I wonder if you always get a new set of delivery valves in the process?

I do not know if changing your secondary fuel filter periodically does extend their lives or not. As a filter gets dirty it presents more resistance to the fuel flow. This may allow dirt to get pushed through.

Other than cleaning some accumulated junk from the surfaces. I do not think we can recondition them at home. I did think of a home test as many members are getting interested in delivery valves.

Safer to test it just with air. Watching the amount of time it takes for say twenty pounds of contained air pressure to dissipate. Then you would not have to guess if they are a problem or not.

A simple kit with a hose and pressure gauge and a shut off. Let the air pressure build to twenty pounds. Shut it off from the air supply and time the decline. Basically just a comparison test.

I do not think that 20 pounds of air pressure leaking down through into the element could do any damage. You may need to rotate the engine for each delivery valve test so the air has an escape route through the elements port. Because air is so compresable you may get no observed drop until you reach a position where the filing port is open.

This test might be reserved until you are just about at your wits end. Or we could have a lot of delivery valves out there that are worn enough. To justify a random check.

There might be a real change by changing any you find bad. You could even check some used ones on a bad used injection pump before using them as replacements.

They are expensive new I think I read somewhere.