Oil Pumps and locking tab washers

[Old ITW]

I'm beginning to reassemble a 964 engine and have a question about oil pump installation. In some of the older engines the oil pump nuts are installed with locking tab washers. With later model engines the locking tabs appear not to be used. Is a nylon locking nut sufficient for oil pump installs?

[boyt911sc]

I never use a nylon lock nut inside a motor. Just buy the metal locking tabs and use them for peace of mind.

Tony

[Henry Schmidt]

Hardened AN washer with prevailing torque nut.

[Dpmulvan]

Porsche calls them oval nuts, other names top lock, acorn et.

[Old ITW]

Thanks to each of you for your responses

[porschedude996]

Metallic Lock Nut rather than Nylon Lock Nut. Belmetric dot com has many all metal lock nuts.

https://belmetric.com/nuts/all-metal-locking-hex-nut/

[Henry Schmidt]

The prevailing torque in prevailing torque locknuts comes from localized plastic deformation to an interference fit with continuous sliding during assembly. Let's break this down.

Localized plastic deformation - Some of the starting threads need to be able to accept the mating part (bolt, say) before the prevailing torque begins. The interference is therefore localized to not include the immediate start of the assembly. For nylon insert locknuts, the interference is only in the nylon ring, and the metal part of the nut is free-spinning; but the interference is the entire internal circumference of the nylon ring. For all-metal locknuts, the threads are plastically deflected such that there are points of interference (1, 2, 3, or 6 points of interference, depending on the configuration of the deflection) with the threads of the mating part.

[porschedude996]

Originally Posted by Henry Schmidt

The prevailing torque in prevailing torque locknuts comes from localized plastic deformation to an interference fit with continuous sliding during assembly. Let's break this down.

Localized plastic deformation - Some of the starting threads need to be able to accept the mating part (bolt, say) before the prevailing torque begins. The interference is therefore localized to not include the immediate start of the assembly. For nylon insert locknuts, the interference is only in the nylon ring, and the metal part of the nut is free-spinning; but the interference is the entire internal circumference of the nylon ring. For all-metal locknuts, the threads are plastically deflected such that there are points of interference (1, 2, 3, or 6 points of interference, depending on the configuration of the deflection) with the threads of the mating part.

Not sure this application needs to be as scientific as you are saying. As a Certified FAA Airframe and Powerplant Mechanic, the spec’s don’t differentiate the between the two nut types. In fact, most Airframe and Powerplant applications don’t even require a torque value that is proven with a torque wrench. This is no different that a fuel pump on the back of a Lycoming IO540. The big clue is when you start getting into fine thread applications.

[Turbo_pro]

Originally Posted by porschedude996

Not sure this application needs to be as scientific as you are saying. As a Certified FAA Airframe and Powerplant Mechanic, the spec’s don’t differentiate the between the two nut types. In fact, most Airframe and Powerplant applications don’t even require a torque value that is proven with a torque wrench. This is no different that a fuel pump on the back of a Lycoming IO540. The big clue is when you start getting into fine thread applications.

"Scientific"?
The best part of this forum is that real Porsche engine builders offer information you may not be aware of. Although most don't need the "scientific" information, more is always better.

[Dpmulvan]

Henry is correct that’s why you should use the lock nut manufacturers compensated torque specs over the Porsche torque specs. We’re splitting hairs here for an oil pump however other applications are more critical.

[Eledaketa]

Originally Posted by Turbo_pro

"Scientific"?
The best part of this forum is that real Porsche engine builders offer information you may not be aware of. Although most don't need the "scientific" information, more is always better.

I agree!

[porschedude996]

I have another tidbit of fastener installation probably unknown to most. And probably even unknown to many in the aerospace biz. We had to torque spacecraft mate to booster and faring to booster bolt applications using angular value tighting. So it a calculated tension based on thread ramp. We used Citric Acid applied to bolt threads and let dry to lube the treads. We used a angular scale to measure.

[reclino]

I would love to read the NASA document calling for citric acid as thread lube. In my little corner of the aerospace world we often use citric acid to pasivate stainless, but this is the first time I have heard it used as a thread lube.
EngiNerding

[porschedude996]

My error, it isn’t Citric Acid, we used Citric Acid to passivate stainless steel. The compound we used as previously listed for lubing fasteners was Cetyl Alcohol.

For those who don’t know or are inquisitive, passivation is used to remove the free iron molecules on the surface of a stainless steel part. Usually because of it being a new freshly machined part. We also used other acids to passivate like Nitrogen Tetroxide also know a N2O4.

As far as NASA, I don’t recall using it when I worked on space shuttle. My experience with spacecraft for the NRO.

And NASA is by no means the pinnacle of aerospace knowledge. NASA is more of a figure head for civilian US aerospace. NASA really doesn’t do much nor bring any technology to the table. Aerospace contractors are the ones who really work at figuring things out. Same with air force and any other military organization. They all hire contractors. NASA is no way the spokesperson for aerospace.