Fuel pump outlet fitting proper tightening question

Junglepilot · #1 09-09-2011, 08:32 PM

Not much experience with Lycoming mech fuel pumps.

That said, I have the 90? fitting with the tap for fuel pressure line and wondering about the tightening sequence for the fitting into fuel pump.

The jam nut that presses the o-ring I understand, but how tight should the actual fitting be.

Right now snug + 1/4 turn leaves the 3/8 male pointing to accessory case which won't allow me to attach fuel line to carb. However concerned that another 3/4 turn may crack FP neck.

Is the purpose of the jam nut to allow for getting the fitting in the right position then allow the jam nut pressing the washer & o-ring to seal the joint without leaking? I added some fuel tank sealant to the threads also.

Thanks

terrye · #2 09-09-2011, 11:05 PM

The threads are parallel threads like a bolt, so I don't think the fitting bottoms against anything, therefore the fitting does not have a tightening torque. The jam nut locks the fitting in place once it is clocked (except for straight fittings) and also acts as a seal for the o-ring. I think the tightening torque of the jam nut would be the same as a hose fitting swivel, Aeroquip has a chart and I think also on Van's site.

Junglepilot · #3 09-10-2011, 05:21 AM

OK, I didn't know that about the parallel threads. It didn't appear to be a pipe thread (tapered).

What I did was turn it in several turns with tank sealant on threads, position it to desired angle, then tightened up the jam nut/o-ring combo as you suggested using good German torque for now (Gutntight). Didn't have the chart, but I'll look on Aeroquip site for that.

Thanks!

Pat Stewart · #4 09-10-2011, 05:25 AM

Quote:

Originally Posted by Junglepilot

OK, I didn't know that about the parallel threads. It didn't appear to be a pipe thread (tapered).

What I did was turn it in several turns with tank sealant on threads, position it to desired angle, then tightened up the jam nut/o-ring combo as you suggested using good German torque for now (Gutntight). Didn't have the chart, but I'll look on Aeroquip site for that.

Thanks!

Not sure about tank sealent, You should position the fitting to align with the fuel hose and tighten the jam nut.

jrs14855 · #5 09-10-2011, 10:39 AM

This is standard Pitts setup. No sealant on threads. The fitting MAY bottom out. If it does I prefer to back it out less than one turn. I have never seen a specified torque for a jam nut with an o ring. It would be pretty hard to get a meaningful torque reading. This same setup is used on many low wing Pipers. Pitts and Piper do not normally pick up fuel pressure at this point.