Throttle Stop Shaft O-ring Size

[jbayer]

Nitrile is Buna-N, which is the o-rings they have on the shelf at the local HW store for plumbing at about 10 cents. Calling it "Military" or "Tactical" does not make it "better." If you look up a chemical compatibility chart for elastomers you'll find that Viton (my top choice for many demanding applications) or PTFE are likely chemically resistant "better" materials considering the wide range of "fuels" people use in these trucks. If you poke around locally, you might have an o-ring or seal outfit that sells to local industrial places. Online with McMaster or other industrial supply places are easy solutions if you can't find them locally.

The -012 seems to be a very close fit, yet the cross-section is a bit over what the NSN info lists as the max. Likely not an issue though. It looks like the original version was Buna-N, so I would expect Viton to last much longer due to it's improved chemical compatibility.

If you want to learn about o-rings and seals, the Parker O-Ring handbook as lots of great info, including SAE and metric standard sizes. Shore A 70-75 hardness is the most common. There's also great design info for static and dynamic seals.

https://www.parker.com/literature/ORD 5700 Parker_O-Ring_Handbook.pdf

Well that' very good information, but, just so you know, I do know a little about Mil #'s, currently still working (29 years, 1 month, 22 days)for one of the top three defense contractors where we build one the carrier based A/C from the ground up.

Mil Spec O-RingsMS29513, superseded by AS29513

(MS stands for MILITARY Standard, and no JO-SCHMO can just call their part "Military" as you put it))

"Packing Preformed O'Ring fabricated from MIL-P-5315P 70 durometer nitrile rubber used in aircraft fuel systems with jet engines (-65 to 200F) Hydrocarbon and fuel resistant." Quoted off the MIL SPEC

 

[mikey]

Looking forward to that write up when you get the time!

Mikey

 

[Wildchild467]

I do not have much to add to this thread other than the "-012" O-ring works great. I think some of the stop shafts that get stuck could have something to do with the o-ring swelling or something sometimes. With my experience with putting the next size bigger o-ring in, it made the throttle sticky. So if anybody is going to pull the over to check to make sure that shaft is not stuck, I would put a new o-ring in it while they are there. It is very easy to do if they do not know the condition of the current o-ring.