bbjordan
Snow Monkey
Sub'd.
CDD DB4 Pump Build
- Thread starter Thewespaul
- Start date
Sub'd.kla94
Registered User
kla94
Registered User
Very interested
K-nite
Registered User
Wes, Thanks for the offer to test my pump, I actually have an old Bacharach test stand that's on my to do list. I've never seen a .450 plunger pump, but the rotor must be different to handle the size. I did see one for sale on E-bay for $2000+ a while back. The plunger bore in our pumps is limited by the leaf spring screw hole depth, so I think the .390 is the safe max, but give it a try. Good luck, Josh.
Thewespaul
Full Access Member
Let me know if you need anything to get that stand going, all we run are Bacharach stands. Good point on the screw hole, I could see that being an issue, I’ll post up the bulletin on plungers I found where I got the part # for the 450s.
Thewespaul
Full Access Member
Got a chance to spend the day at the fuel shop running the db4 on monday, our current setup is:
-Highest fuel delivery shoes
-Both leaf springs bottomed out
-Marine 6.2 cam ring flipped for 7.3 rotation
-Maring 6.2 cam pin installed
-#12 advance piston machined for db4 cam pin
-Transfer pump in place with standard light load advance
Checked our main fuel setting first to get an idea of how it was going to run (1400 rpms) and as soon as we started running it up to speed it pegged our housing pressure gauge, and our advance reading pegged all the way retarded. Stopped the stand and found our advance piston was stuck, but the cam ring could still pivot with the top off so we knew the cam pin wasnt snapped. Went to pull the cam pin out and it was stuck, odd. Took a moment to realize the inner plunger the light load advance arm acts on was stuck on a chamfer on the db4 cam pin, which was binding the advance plunger and forcing all the way retarded once the transfer pressure came up, which opened to lube passage up to the housing which dumped all the housing pressure out the return, which spiked the housing pressure. So theres no way the 6.2 cam pin can work with the timing unlocked, we took an ag db4 cam pin off the shelf that doesnt have that chamfer and installed it in place of the 6.2 cam pin. The ag cam pin is actually a bit more girthy, and doesnt have the any interference with the inner plunger on the advance piston.
With that installed, our advance seemed to work properly again, and we ran it up to test main fuel. We got 110 cc with the pump at temp, the same as it made when it grenaded the db2 cam pin previously. Rather disappointed we started fiddling with it trying to nurse more fuel out of it without having to pull it down to pull the leaf springs. Gutting the return fitting, playing with some governor mods I recently came up with on my db2 build for the shop truck, and bumping up our transfer pressure got us to 130-135cc for our main fuel. Seems we are just limited too much by the leaf springs so we are tearing the pump down to run it again without them once I can clear another day to spend at the fuel shop. We did test hot start cranking spec to check the condition of this brand new db4 head and rotor and set a new rotary pump record, 185cc at 150 rpms, this thing wont have any issues hot starting thats for sure. More to come.
-Highest fuel delivery shoes
-Both leaf springs bottomed out
-Marine 6.2 cam ring flipped for 7.3 rotation
-Maring 6.2 cam pin installed
-#12 advance piston machined for db4 cam pin
-Transfer pump in place with standard light load advance
Checked our main fuel setting first to get an idea of how it was going to run (1400 rpms) and as soon as we started running it up to speed it pegged our housing pressure gauge, and our advance reading pegged all the way retarded. Stopped the stand and found our advance piston was stuck, but the cam ring could still pivot with the top off so we knew the cam pin wasnt snapped. Went to pull the cam pin out and it was stuck, odd. Took a moment to realize the inner plunger the light load advance arm acts on was stuck on a chamfer on the db4 cam pin, which was binding the advance plunger and forcing all the way retarded once the transfer pressure came up, which opened to lube passage up to the housing which dumped all the housing pressure out the return, which spiked the housing pressure. So theres no way the 6.2 cam pin can work with the timing unlocked, we took an ag db4 cam pin off the shelf that doesnt have that chamfer and installed it in place of the 6.2 cam pin. The ag cam pin is actually a bit more girthy, and doesnt have the any interference with the inner plunger on the advance piston.
With that installed, our advance seemed to work properly again, and we ran it up to test main fuel. We got 110 cc with the pump at temp, the same as it made when it grenaded the db2 cam pin previously. Rather disappointed we started fiddling with it trying to nurse more fuel out of it without having to pull it down to pull the leaf springs. Gutting the return fitting, playing with some governor mods I recently came up with on my db2 build for the shop truck, and bumping up our transfer pressure got us to 130-135cc for our main fuel. Seems we are just limited too much by the leaf springs so we are tearing the pump down to run it again without them once I can clear another day to spend at the fuel shop. We did test hot start cranking spec to check the condition of this brand new db4 head and rotor and set a new rotary pump record, 185cc at 150 rpms, this thing wont have any issues hot starting thats for sure. More to come.
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IDIBRONCO
IDIBRONCO
185cc? 
That could almost power two engines for me!
That could almost power two engines for me!
Thewespaul
Full Access Member
We got the pump torn down a few weeks back and pulled the leaf springs out to get full stroke with all four plungers to try and get the fuel we are after and made 200cc at cranking, but made no more than previously at our main fuel setting (1400 engine rpm) but found the issue almost instantly. Now with the plungers moving so much fuel we found the transfer pump was not able to maintain proper transfer pressure to fully fill the charging chambers at any significant rpms. We boosted the inlet pressure using the stand's supply pump set at 50 psi and got a pretty good gain in fuel but transfer pressure never exceeded 60 psi. We took a return flow reading and with the return gutted it was ******* the stand's flow meter and with a non gutted return the housing pressure exceeded 20 psi with still very high return flow. I know with my work on the 150cc db2 that the transfer pump can supply more than enough fuel flow so it had to be bypassing transfer pressure to the housing side somewhere in the pump. Going back over my notes I found that I started having increasing low transfer pump readings after boring out the advance piston for the db4 cam pin, so its got to be the tolerance in the cam pin to advance piston bore was allowing transfer pressure in the passage for the light load advance plunger in the advance piston marked in blue was leaking through to the other passage marked in red which goes to the opposite end of the advance piston, which is only exposed to housing pressure
We originally had bored this out with a mill, and had a really tough time at it with how hard the material is, I knew EDM would be the best route, but I wasnt finding a shop that was willing to take a small project on like this. Well with some work I found a shop that would do it, I had to find a tolerance for them to machine it to, so I worked backwards with an already very hard to source DB4 marine advance piston, and found a company that distributed aftermarket, new advance pistons for stanadyne. I got through to their engineering department, explained what I was doing and he was able to get me a spec to machine the bore to. I wont give away exactly what that spec is, but its a tolerance window of less than a fifth the diameter of a human hair, just not possible with a mill and cobalt bits.
Here is the finished product with the 7.3 advance piston machined for the larger cam pin, you can see the difference in width around the barrel of the pin, about 7/16 vs 3/8, but more importantly is the ball end which fits into the cam ring, it is much larger than the db2 end, which is the weak point where they break.
Now we should have our transfer pump pressure fixed, we should have this in the pump and on the stand next week, Ill update with more numbers once we have them.
You must be registered for see images attach
We originally had bored this out with a mill, and had a really tough time at it with how hard the material is, I knew EDM would be the best route, but I wasnt finding a shop that was willing to take a small project on like this. Well with some work I found a shop that would do it, I had to find a tolerance for them to machine it to, so I worked backwards with an already very hard to source DB4 marine advance piston, and found a company that distributed aftermarket, new advance pistons for stanadyne. I got through to their engineering department, explained what I was doing and he was able to get me a spec to machine the bore to. I wont give away exactly what that spec is, but its a tolerance window of less than a fifth the diameter of a human hair, just not possible with a mill and cobalt bits.
Here is the finished product with the 7.3 advance piston machined for the larger cam pin, you can see the difference in width around the barrel of the pin, about 7/16 vs 3/8, but more importantly is the ball end which fits into the cam ring, it is much larger than the db2 end, which is the weak point where they break.
You must be registered for see images attach
Now we should have our transfer pump pressure fixed, we should have this in the pump and on the stand next week, Ill update with more numbers once we have them.
IDIBRONCO
IDIBRONCO
So is that chamfer around the 3/8" hole important? I noticed that it's not there on the "about 7/16"" hole. That's a big difference on hole sizes on a part that small.
Thewespaul
Full Access Member
Yes, the first db4 cam pin had one and gave us troubles, it’s a chamfer for the inner advance plunger that the light load advance acts on, with the chamfer the plunger would snag and keep the piston from sliding over. Going with this ag style db4 cam pin that has no chamfer eliminated that issue, it required us to rewrite the light load advance settings a bit to accommodate for less travel in the inner plunger but it’s doable without any modifications to the light load advance setup.So is that chamfer around the 3/8" hole important? I noticed that it's not there on the "about 7/16"" hole. That's a big difference on hole sizes on a part that small.
IDIBRONCO
IDIBRONCO
Not that I'll ever build an engine that requires a DB4 for fuel, but it's cool reading about it anyway.
Thewespaul
Full Access Member
Thanks brother, lookin forward to hearing that bronco run
Garbage_Mechan
Garbage Mechanic
36 years after their debut someone has found the time and patience to really understand the pumps. Thanks Wes! I’m sure Mel from Connestoga helped push this a long as well as others.
Thewespaul
Full Access Member
Thank you sir, Justin at R&D has been a help in this project, letting me bounce ideas and questions off him from time to time and sharing info on his own pumps, as well as @Goose_ss4 whos keeping the show goin. As of right now, I’m the only pump rebuilder that offers a warrantied db2 with more than 100cc, and in the next few months I’ll be setting up my test stands in house which is going to allow me to make these pumps a bit more affordable, as well as give me the ability to spend some time on some other ideas I have to really push the db2 platform, I’ve got a db2845 that needs to be built after this for the race truck
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