Possible cause of “nailing” after crush washer and "O" ring replacement - PeachParts Mercedes-Benz Forum

Diesel911 · #1 03-10-2008, 07:15 PM

I am going to add some speculation: The delivery valves have seats that they ride in (they do not rotate) and wear in to their seats. When you remove them and (I hope) clean them they do not go back into exactly the same position (of course each delivery valve has mated parts that should not swapped around) so the seats that they wore into are now disturbed.
I am speculating that the sound goes away after X number of miles for most people after these valves have worn themselves a new seat (reseated themselves).
Colud the delivery vlaves be scribed with a mark so that the valve parts go back into the same position?
Could the delivery valves be reseated with some very fine lapping compoud (500-600 grit) only on the seating area (as engine valves are lapped) before being reinstalled and the "nailing" eliminated?

pimpernell · #2 03-11-2008, 12:03 PM

I definetly feel that you are on the right track. I did my delivery valves, and prior to the repair, the engine could not be heard at idle. After the repair, there was slight nailing at idle and when going about 15mph and taking your foot off the throttle. There was no issue with smoke, nailing, or power at highway speeds. I redid the valves, and the nailing has almost gone away. In almost every post you read about the delivery valve repair, the writer indicates that after the job, nailing that was not present suddenly appears. The other area that would support your idea is the fact that when the engines are started from cold, as long as the glowplugs are active, the nailing is not heard. Once the glowplugs dissengage, the nailing immediatley follows. That would correspond with the idea of extra fuel getting to the injectors. As long as the glow plugs are activated, this extra fuel is no problem, but when they are deactivated, this extra fuel causes the nailing sound.

Diesel911 · #3 03-11-2008, 03:18 PM

Quote:

Originally Posted by pimpernell

I definetly feel that you are on the right track. I did my delivery valves, and prior to the repair, the engine could not be heard at idle. After the repair, there was slight nailing at idle and when going about 15mph and taking your foot off the throttle. There was no issue with smoke, nailing, or power at highway speeds. I redid the valves, and the nailing has almost gone away. In almost every post you read about the delivery valve repair, the writer indicates that after the job, nailing that was not present suddenly appears. The other area that would support your idea is the fact that when the engines are started from cold, as long as the glowplugs are active, the nailing is not heard. Once the glowplugs dissengage, the nailing immediatley follows. That would correspond with the idea of extra fuel getting to the injectors. As long as the glow plugs are activated, this extra fuel is no problem, but when they are deactivated, this extra fuel causes the nailing sound.

Thank you for your comment. I am surprised more people have not said anything even if it was to disagree with me.
I do not think that the nailing is being caused by too much fuel; I think it is being caused by a change in the timing due to the delivery valves not seating well and allowing some fuel to seep back (causing less fuel delivered and at less pressure) causing the fuel to be injected later starting ignition later and causing the nailing.
I believe that when the glow plugs are on it speeds up the ignition to the extent that less fuel is burning later. In the same way the glow plugs on a cold day if used long enough stop the injectors from nailing during a cold start.
I do not recall the specific details (I have seen several threads on this) there are at least 3 stages of the ignition of the fuel when it is being injected. If for some reason; like a spray nozzle with a worn seat is not atomizing well there is a lot of unburned fuel left at the last of the 3 stages. When an abnormal amount of fuel burns at that end stage you get the loud knocking or nailing sound and this is what I think is happening due to the delivery valves not seating due to being disturbed.
Another aspect is that the delivery valve helps to regulate the shock wave that is created when fuel injection stops. The whole injection system from plungers and barrels to the spray nozzles is engineered to produce specific results. If something along the line changes it can cause unforseen results.

lrg · #4 03-12-2008, 01:24 AM

Diesel911,
I think that's a very reasonable hypothesis. If correct I wonder if I should stop using fuel additive for a while to help speed my recently disturbed delivery valves to "bed in".

michael cole · #5 03-12-2008, 12:16 PM

I too agree with your hypothesis that correct mating of the contact surfaces of the delivery valve would be needed to ensure fuel delivery pressure and timing.i would have assumed the copper crush washer would take care of this.but now im doubting.i do know if you over torque the delivery valve in an attempt to obtain a better seal you will risk distorting the aluminum IP housing.if this happens it may be impossible to get a good seal

TMAllison · #6 03-12-2008, 12:35 PM

Interesting thoughts.

I also feel that residual rubber particles remaining in the pump body from the deterioated o-rings is a contributing factor. You can have everything sparkling clean before removal and rinse the valve holder numerous times before reinstalling but will still have contaminated fuel that remains inside the lower portion of the valve.

When restarted those particles end up at the inj.

Iin an attempt to avoid this I've suggested more recently that once the DV's are back together a few ounces of fuel be pumped out before the hard lines are reconnected to the inj's.

nhdoc · #7 03-12-2008, 12:54 PM

Does anyone really know what the function of the copper crush washer is? It appears to me that it doesn't really get crushed, so calling it a crush washer may be incorrect. It seems more to act as a "bearing" surface between the spring and the DV plunger part. I've always questioned the necessity of replacing the washer since, as I said, it never gets crushed and don't think it will even wear out. I don't even see it pictured in that drawing in post #1 of this thread. I wonder what would happen if it was left out completely?

I always assumed it allowed the plunger piece to rotate if it wanted to since having it be between the bottom of the spring and the top of the plunger allows the plunger to slide against the washer instead of the bottom of the spring - where it could get snagged on the end of the spring wire or the spring itself could wear into the top of the plunger piece if they were in constant contact with one another. I'd love to know if someone actually knows the exact purpose of that copper washer in there.

lrg · #8 03-12-2008, 01:11 PM

Quote:

I also feel that residual rubber particles remaining in the pump body from the deterioated o-rings is a contributing factor. You can have everything sparkling clean before removal and rinse the valve holder numerous times before reinstalling but will still have contaminated fuel that remains inside the lower portion of the valve.

I agree. Short of dismantling the whole IP I think it's impossible to get it 100% clean after a delivery valve O-ring replacement. When you consider the secondary fuel filter is there to filter out exactly that sort of very fine grit it makes sense that there would be some impact related to it being downstream from the filter. Even cranking to clear out the injectors may not get it all.

A good way to know if this is a factor would be if someone had all their injectors rebuilt/replaced a few 100 miles after a delivery seal job. I assume you'd need some miles after the DV work to allow all the particles to clear out of the IP. Anyone out there done that? If so did the nailing get softer or stop after the injectors were replaced?

Diesel911 · #9 03-12-2008, 03:55 PM

Quote:

Originally Posted by nhdoc

Does anyone really know what the function of the copper crush washer is? It appears to me that it doesn't really get crushed, so calling it a crush washer may be incorrect. It seems more to act as a "bearing" surface between the spring and the DV plunger part. I've always questioned the necessity of replacing the washer since, as I said, it never gets crushed and don't think it will even wear out. I don't even see it pictured in that drawing in post #1 of this thread. I wonder what would happen if it was left out completely?

I always assumed it allowed the plunger piece to rotate if it wanted to since having it be between the bottom of the spring and the top of the plunger allows the plunger to slide against the washer instead of the bottom of the spring - where it could get snagged on the end of the spring wire or the spring itself could wear into the top of the plunger piece if they were in constant contact with one another. I'd love to know if someone actually knows the exact purpose of that copper washer in there.

(Please see FIG-11 only)-The purpose of the Copper Crush washer is to provide a seal between the top of the Delivery Valve Support-item 5 and the Pressure Valve Holder- item 1. The Copper Crush washer is exposed to the same pressure as the injectors and in fact it is possible for the high pressure to erode the crush washer.
The reason the Crush Washers need to be changed is that in order form a seal the copper compresses conforming to any irregularities between the Pressure Valve Holder and the top of the Delivery Valve Support. Ounce used the Crush Washer is in a sense deformed to fit; and also when squashed down during the torque procedure the Crush Washer becomes work hardened and is no longer as soft as before (meaning if you use it again it may not seal well).
Also I believe that the Crush Washers are some stiffer alloy that is not as soft to begin with as stay the copper washers on your fuel filter banjos. (If you heat these red hot and let them cool they become soft again and can be reused.)
Back to the picture- There are the words “Lapped Surface” with 2 lines pointing to where the lapped surface is. Below that parting line is where the Plunger and Barrel Assembly; the plunger part of this is the part that rotates.
Also the Lapped Surface area if lapped properly dose not need any sort of seal do to a precision fit between the bottom of the Delivery Valve Support and the top of the Plunger and Barrel.
Item number 3 the Delivery Valve Cone; the part that we call the delivery valve dose not rotate it just goes up and down.

Diesel911 · #10 03-12-2008, 04:01 PM

Quote:

Originally Posted by TMAllison

Interesting thoughts.

I also feel that residual rubber particles remaining in the pump body from the deterioated o-rings is a contributing factor. You can have everything sparkling clean before removal and rinse the valve holder numerous times before reinstalling but will still have contaminated fuel that remains inside the lower portion of the valve.

When restarted those particles end up at the inj.

Iin an attempt to avoid this I've suggested more recently that once the DV's are back together a few ounces of fuel be pumped out before the hard lines are reconnected to the inj's.

YES. Open the hard lines at the injectors and crank the engine until you are getting good spurts of fuel out of the line; cleans out the lines and bleeds the air out at the same time.

Diesel911 · #11 03-12-2008, 04:13 PM

Quote:

Originally Posted by michael cole

I too agree with your hypothesis that correct mating of the contact surfaces of the delivery valve would be needed to ensure fuel delivery pressure and timing.i would have assumed the copper crush washer would take care of this.but now im doubting.i do know if you over torque the delivery valve in an attempt to obtain a better seal you will risk distorting the aluminum IP housing.if this happens it may be impossible to get a good seal

(Please see FIG-11 only)- The sealing area that I was referring to is actually the area between the Delivery Valve Cone- item #3 and the Delivery Valve Support-item #5 with the sealing area being at item #4 which is a Steele metal to Steele metal contact (some what like a valve in the cylinder head except the spring pushes down on it instead of pulling it up.) The copper crush washer should not be touching the Delivery Valve cone and should be sealing item #1 and #5.
And, Yes over tightening can damage the aluminum pump housing.

nhdoc · #12 03-12-2008, 04:23 PM

OK, I see now what the crush washers do, thanks. Looking at the photos in this wiki again helped refresh my memory:

http://www.peachparts.com/Wikka/OM606DeliveryValveSeals

My problem was I didn't see how the crush washer got centered over the plunger part when you screwed the DV cover on but it looks like it is tapered some to help. I wonder if some people who have terrible troubles after doing the job muck up the centering of the copper washer and that's what causes poor running since that might interfere with the operation of the plunger part?

Diesel911 · #13 03-14-2008, 01:21 AM

Quote:

Originally Posted by nhdoc

OK, I see now what the crush washers do, thanks. Looking at the photos in this wiki again helped refresh my memory:

http://www.peachparts.com/Wikka/OM606DeliveryValveSeals

My problem was I didn't see how the crush washer got centered over the plunger part when you screwed the DV cover on but it looks like it is tapered some to help. I wonder if some people who have terrible troubles after doing the job muck up the centering of the copper washer and that's what causes poor running since that might interfere with the operation of the plunger part?

You will need to look up the DV assembly for your specific engine/IP there is some as they are not all the same.

lrg · #14 03-14-2008, 12:23 PM

On my '87 I put the washer in the pressure valve holder with a drop of diesel to hold it in for assembly. The PV holder has a collar inside that the crush washer sits on so it's almost impossible for it not to center properly if you assemble it that way.