The Cessna 120-140 Association Forum

Just replaced the sump with a repaired one. It has a silicone gasket. Recommended fastener torque is 15 in-lb, which is only slightly more than finger tight. What do people use to lock these nuts at such low torque? I am concerned star washers may not provide enough spring. Leaning toward metal lock nuts. Thanks.

For the sump I prefer MS21042-4 nuts. They're all metal stop nuts and have a reduced size hex for easier installation in tight quarters.

6643 wrote: ↑Sun Nov 26, 2023 3:39 pm For the sump I prefer MS21042-4 nuts. They're all metal stop nuts and have a reduced size hex for easier installation in tight quarters.

Thanks this is helpful. Apparently the factory use the elastomeric ones but the metal seems more secure.

Some sort of locking nut is really important for anyone using tbe silicone gasket.

My oil sump was leaking so I purchased a new "Real Gasket" and removed the sump thinking that the gasket was the problem, this was not the case. the old gasket was in excellent condition but there was very little tension on the locknuts that secured the tank. Because I have drilled oil tank stud bolts I installed the new gasket and the tank using AN310-4 castle nuts torqued to the specified 15 in. pounds and then safety wired the nuts.
The safety wire was a real pain to install so I'm thinking that I'll use cotter pins when I check the torque in the future.

I ended up using these fasteners: https://www.chiefaircraft.com/hd-nas679a.html They seem fine for the load and also a bit lighter than the solid locknuts.