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+--- Thread: Fuel leak from top of gear pump head (/showthread.php?tid=7266)
RE: Fuel leak from top of gear pump head - Rawze - 04-17-2021
(04-17-2021 )SquareOne Wrote: So, once again cleaned it thoroughly and let the truck run. Very very subtle, but looks like the fuel is creeping through the threads of the torx plug. Grabbed the torque wrench and moved up in small increments to see the force it would take to remove it. Seems like it broke free at about 85ft/lbs. (I used a t60 socket....I believe a T65 would be perfect, but only had a 60 and 70 in that range. Cummins may have a specific tool as the ends are squared rather that pointed like a traditional torx bit).
Here are a couple pics I took of the removed plug. Seems to press on a spring loaded valve below inside the cavity. Also appears that it’s a machined surface seal. The plug has some very light marking within the center (maybe this is the issue?). Once tthe weather clears I’ll get some more pics and try to clean, reinstall and torque.
(speculation)...
It is likely a metal-to-metal "crush-fit" one time use seal, given that it likely has to hold back 40,000+ PSI.
Given it also has the same thread height as it does thread depth (providing no resistance to over-torquing at all) ... It will strip very easily if you over-torque it by very much. You need to measure the diameter and thread pitch ... Then find a screw/torque chart of screws of that size and pitch, showing different materials and get some references of what the max should likely be vs. what you measured.
RE: Fuel leak from top of gear pump head - SquareOne - 04-17-2021
I was afraid of the one time 'crush fit' as well, and my assumption is 'blank stares' if I ask the local Cummins store about purchasing (or even locating for that matter) a replacement. I'll do some research on the thread pitch/size in order to get the correct torque. There was no sealant or other product used on the threads so once the initial break, it literally came out with 2 fingers.
I'm going to inspect the threads within the head as well once the weather calms down to see if they are compromised. Looks like I'll be putting a head on it if this removal and re-torque doesn't work. I almost bought an entire head assembly with the last rebuild, just for the hell of it....
** Plug is a 3/4" Diameter with 16tpi. There is 7/16" of threaded surface. It is steel, but don't know the grade.
RE: Fuel leak from top of gear pump head - SquareOne - 04-17-2021
This is inside the head where the plug in inserted. Plug secures a small spring which holds down a check valve, possibly?
I used 3000 grit paper and cleaned the mating surface of the minor imperfections it had. Crossing my fingers with this one as I have no clue if it’s going to do anything. Will update after reinstall.
RE: Fuel leak from top of gear pump head - SquareOne - 04-18-2021
Reinstalled yesterday at around 10a once the weather allowed. Like mentioned earlier, cleaned the threads (which had no visible debris or imperfections), cleaned the mating surfaces, added a high temp chemical resistant sealant on the threads and torqued it down to 100ft/lb.
Based off the charts I found online, I went with the lowest torque number available (approx 102ft/lb) using the thread pitch, diameter, and surface area of thread. I used the lowest since I didn't know the grade of this plug. Last thing I want is to strip the head or plug. Again, it took about 85ft/lb for removal.
I applied the sealant (although it didn't have any to begin with) just as an additional measure. Careful to cover the entire threaded surface, but ensure none was on the machined mating surface of the plug. Could be a absolute waste of time, but hell, worst case scenario is I'm putting a head on the damn thing anyway so, what have I got to lose by giving it a shot. I'll wait a full 48 for the cure. Using a small space heater to keep the temp around 80-90 degrees to assist with cure. Sealant claims chemical resistant and heat resistant to 400degrees. I figure if it ever reached 400 or better, I'd have a lot more on my hands than this fuel pump issue lol.
RE: Fuel leak from top of gear pump head - tree98 - 04-18-2021
Seems like the plug would need a certain torque spec to apply an exact pressure to that spring(relief type valve I'm guessing). To tight it might wipe out the pump no ? Maybe should have counted the turns when taking it out. Hope it works for you though.
RE: Fuel leak from top of gear pump head - Rawze - 04-18-2021
(04-18-2021 )tree98 Wrote: Seems like the plug would need a certain torque spec to apply an exact pressure to that spring(relief type valve I'm guessing). To tight it might wipe out the pump no ? Maybe should have counted the turns when taking it out. Hope it works for you though.
If the plug was an adjustment for the spring then there would be another means of sealing it .. thread sealant or some other separate seal like a high pressure turcon o-ring, etc.
looked like the plug bottomed out against a metal-to-metal tapered seal. Spring tension is not adjustable if this is the case.
RE: Fuel leak from top of gear pump head - Mattman - 04-18-2021
May be a torx plus that fits the torx shaped head. Why do they make a torx and a torx plus I can't tell you but they do.
CAT uses torx plus on their peanut cover for the camshaft gears.
Horton uses torx plus on their fan clutch hub bolts.
RE: Fuel leak from top of gear pump head - Shotgun74 - 04-18-2021
I replaced the entire pump when my fuel pump leaked out of those exact same torx plugs on a new fuel pump that was a few months on the truck when I started smelling fuel in the cab & upon inspection you could watch the fuel pool up through those torx plugs. I wasn’t playing around with that pump possibly going out & taking the motor with it. My way of thinking was if it’s leaking there what else is weak in the fuel pump that would rear it’s ugliness in time. Thankfully the fuel pump was still under warranty & if it wouldn’t have been I still would’ve replaced it.
Good luck on what you decide.
RE: Fuel leak from top of gear pump head - SquareOne - 04-19-2021
(04-18-2021 )Shotgun74 Wrote: I replaced the entire pump when my fuel pump leaked out of those exact same torx plugs on a new fuel pump that was a few months on the truck when I started smelling fuel in the cab & upon inspection you could watch the fuel pool up through those torx plugs. I wasn’t playing around with that pump possibly going out & taking the motor with it. My way of thinking was if it’s leaking there what else is weak in the fuel pump that would rear it’s ugliness in time. Thankfully the fuel pump was still under warranty & if it wouldn’t have been I still would’ve replaced it.
Good luck on what you decide.
While I agree that whatever the truck needs, it should get (it is our livelihood after-all), I don't believe I'll replace the whole pump if this doesn't work. The head certainly, but even as overly maintenance oriented and cautious as I am, I don't see the need to replace the main portion of the pump without issue. I've been inside the pump at the 250k mark and once again just recently at the 450k mark, both times replacing the guts and inspecting the lobes carefully with no sign of wear much less any damage.
Someone can correct me if I'm wrong, but aren't the large majority (if not all) of failures due to the 'breaking down' of the lobes, rollers, and old ceramic plungers running throughout the lube system? In another post from a couple years back I even challenged if it really was the ceramic (on the older style) causing the issue or if it was just a secondary effect of the main issue , which IMO was the old style roller pins failing. My theory was that the older style roller pins failed causing erratic behavior between the roller and lobe, thus causing degradation between the 2. The erratic 'chattering' would then lead to the destruction of the ceramic plungers....plungers get the blame, but the rollers were the primary culprit---again, just my opinion. As a side note, the updated components had different plungers and DLC coated roller pins(Unilevers knew more about this) as an update. Any older style fuel pump failure pics I have seen have the roller pins destroyed.
Again, not saying there's anything wrong with replacing the entire pump, just don't see the need to given what we know.