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Vintage Diesel and Oil Engines Fairbanks Morse, Lister, Petter, Witte and other pump injected Diesel oil engines.

Vintage Diesel and Oil Engines

CAV DPA Injection Pump - Nothing From the Upper Bleed Screw


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  #1  
Old 03-28-2018, 07:09:47 PM
Joe Stewart Joe Stewart is offline
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Default CAV DPA Injection Pump - Nothing From the Upper Bleed Screw

This injection pump is on a 1964 David Brown 990 implematic farm tractor. The seller told me that the tractor "needs a new injection pump", but he did not tell me exactly what was wrong with it. I dragged the tractor home and started experimenting. I drained the old diesel fuel out of the tank and replaced it with fresh fuel. I used the hand primer pump on the side of the block to bring fuel to the injection pump. I ran the fuel line into a glass jar to confirm that I am getting tons of solid fuel to the injection pump with no air bubbles. I began to bleed the pump by loosening the lower bleed screw (circled in red) and I was successful in bleeding out all the air and getting plenty of solid fuel to spurt out. Then, I focused attention on the upper bleed screw (circled in blue). When I loosen this screw and pump the hand pump, I get nothing to come out of that screw - no air, no bubbles, no fuel, no nothing. I can completely remove that screw from the housing while pumping the hand pump and still nothing comes out. I'm pretty sure this is not normal. This model pump is used on seven other diesel engines that I own and I am pretty sure that fuel should be flooding that upper case portion of the pump during normal operation.

Furthermore, I am getting no fuel out of the return line (none whasoever, not even a drop).

I am beginning to think that this pump might have an internal obstruction to fuel flow? Calling all CAV DPA experts: Does anyone know specifically what might be causing this symptom? Any input appreciated.
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  #2  
Old 03-28-2018, 10:32:44 PM
Heins Heins is offline
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Default Re: CAV DPA injection pump - nothing from the upper bleed screw

You might loosen one fuel line to one injector, remove the bleed screw circled in blue, and run the starter while you pump the hand pump.
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Old 03-29-2018, 07:25:54 AM
Oil Power Oil Power is offline
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Default Re: CAV DPA Injection Pump - Nothing From the Upper Bleed Screw

I would not be concerned about no fuel from the upper bleed screw. Fuel only reaches this bleeder when the whole pump is full of fuel which either comes from normal internal leakage within the pump or a back flow from the return side of the filter. Different plumbing on various engines will sometimes mean fuel reaches the top bleeder sooner. You should loosen all the injector pipes and see if you can get pulsing delivery when you crank the engine. If not it is most likely the metering valve is stuck in the shut off position. Keep the throttle in the full speed position. Moving the stop lever to stop and back to run position a few times, can sometimes free a stuck metering valve but you would have to be lucky. If you felt confident the metering valve can be serviced by removing the cover from the pump but there are several traps to fall in so it is best to remove the pump and have it serviced by your fuel injection specialist. Other causes of the pump failing to pump would be stuck plungers or a seized head that has sheared.
Hugh
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Old 03-29-2018, 08:23:45 PM
Joe Stewart Joe Stewart is offline
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Default Re: CAV DPA Injection Pump - Nothing From the Upper Bleed Screw

OK Thank you to oil power and Heins. I will try your recommendations after I get the cylinder head back on. I just re-installed the pistons today with new rings (I forgot to mention that the motor was frozen from rain water entering the uncovered exhaust- seller "forgot" to inform me of this). The starter is shot, so I will have to "pull start" it to bleed the lines. I will probably get around to this in the next couple of weeks, as these projects move slowly (too many projects, etc etc). Thanks again and will post back to let you know what transpires.

Also forgot to mention that I've removed the top cover on several of my other DPA pumps (in order to install new o-rings on the leaking throttle shaft and fuel cut off shaft). I'm aware of the little spring in there with the three holes. I've never completely disassembled one of these pumps, but may experiment with one that I have sitting on the shelf out in the garage.
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Old 03-30-2018, 05:00:38 AM
oldgoat oldgoat is offline
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Default Re: CAV DPA Injection Pump - Nothing From the Upper Bleed Screw

There is a video on youtube about a stripdown of a dpa pump look for the one by" bundy bears shed"
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Old 03-30-2018, 07:00:17 AM
Joe Stewart Joe Stewart is offline
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Default Re: CAV DPA Injection Pump - Nothing From the Upper Bleed Screw

Oldgoat: Yeah, I've watched the majority of that excellent video. He does a great job of going through it step by step, and he's a real likable fellow. I'm going to reseal one of my DPA pumps using his video. Here's the link:

https://www.youtube.com/watch?v=h26p78YZIr4&t=2007s
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Old 04-22-2018, 01:29:55 PM
Joe Stewart Joe Stewart is offline
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Default Re: CAV DPA Injection Pump - Nothing From the Upper Bleed Screw

OK, thank you for all replies!. I tried to prime and start engine without bleeding the upper bleed screw. Would not bleed or start. So I removed pump and disassembled it.

I discovered that the carbon fiber vanes were missing from the vane pump section (previous owner did this) and there was a healthy chug of water at the bottom of the pump.

I used the Bundy Bears Shed video as a guide. I installed new front seal and torqued up retaining screw. I then put a new o-ring on the pump head and slid it into the aluminum housing of the pump. See photo. The problem I am having is that I cannot line up the three retaining bolts that hold the pump head to the aluminum housing. See red arrow in photo.

It looks like the pump head needs to slide about 0.25mm more into the housing, but I cannot get it to go in any further. I've taken off and re-installed this pump head three times to look for the reason why it won't go any farther, and I cannot see any obstructions.

Posting here to see if anyone has any ideas.
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Old 04-22-2018, 04:28:50 PM
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Marcel P Marcel P is offline
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Default Re: CAV DPA Injection Pump - Nothing From the Upper Bleed Screw

Can't help you with the housing but without the vanes it probably was not gonna work. Another problem that occured with these DPA pumps was that the plungers got stuck in the upper position from standing. The easiest way to unstuck them is to connect an injector testing pump and while it is under pressure rotate the pump slowly until you hear the plunger popping back. I think this pump also has a regulator that regulates the fuel delivered by the vane pump, this contains a small valve that can get stuck as well.
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Old 04-24-2018, 08:30:16 AM
Oil Power Oil Power is offline
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Default Re: CAV DPA Injection Pump - Nothing From the Upper Bleed Screw

Joe, have you had the cam ring and timing circlip out of the housing? Could be the circlip is not installed properly. Check if the head is coming up against the cam ring, or is it being held out by the drive shaft. Re check assembly of all parts.
Hugh
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Old 04-24-2018, 07:00:56 PM
Joe Stewart Joe Stewart is offline
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Default Re: CAV DPA Injection Pump - Nothing From the Upper Bleed Screw

I never removed the cam ring or the circlip. Left them in place. The cam ring is mobile even after I have the pump head fully pressed in. I can partially rotate the cam ring, but there is a stud attached to it which sticks out the bottom of the pump (visible in above photo) which prevents rotating to a greater degree.

I am almost certain that it is the MAIN DRIVE SHAFT which is preventing me from pushing the pump head in.

But I cannot imagine how it "fit before but it doesn't fit now".

I am guessing that I need to pull the "drive hub" off the front of the pump again and have a good look at its internal splines. May be a piece of trash in there that I missed, which is preventing main drive shaft from being pulled forward.
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