Discussion in '6.9L IH & 7.3L IDI Diesels' started by Thewespaul, May 18, 2019.
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.
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.
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.
185cc? That could almost power two engines for me!
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