Fuel leak from top of gear pump head

[Rawze]

(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.