What I learned about pipe thread building the m/c lift.

[John Ranalletta]

Bought a bigger air spring and it arrived with the strangest fitting I've ever encountered as it has internal and external threads.  Unlike the first spring that used NPT (universally available National Pipe Thread) this called for either  a 3/4-UNF or a 1/4-18 NPTF.  Raise your hand if you have either of these in your kit.  As it turns out, the only source for the smaller one is a vendor to Grainger.  Just picked them up but not tested yet.

 

       

So, you might wonder what's the diff between NPT and NPTF.  The F stands for fine which means the threads are machined vs. rolled NPT threads.  NPT requires a sealant like Teflon tape or pipe dope.  The NPTF does not.   Can you use NPT and NPTF together?  Well?  Depends upon who you ask.  Members on some forums said to apply the tape and tighten.  Experts on thread design say, "No, no, Nanette".

 

In the picture comparing the two abpve notice the blunt threads on the NPT vs the sharper threads on the F.  There are other differences in pitch, etc.

 

Now, I just hope they hold air.  Lesson's over.  As you were.

 

 

[DakarTimm]

https://omega1.com/blog/npt-and-nptf-thread-connections-whats-the-difference/#:~:text=The primary difference between these,temperatures%2C contaminating fluids and gases.

 

[Joe Frickin' Friday]

From this page:

 

Quote

How NPTF Threads Work

 

Crests of the threads are crushed against the mating thread roots when assembling NPTF threaded components. This crushing is in addition to the interference fit provided by the thread taper wedging the thread flanks together. Like NPT connections, tapered threads hold NPTF connections together. And these connections are solid and tight. Crushing the thread crests fills the potential spiral leak path in NPT connections. Filling this leak path is why NPTF connections do not generally need thread sealants and why NPTF is considered a dryseal connection.

 

 

It looks like you could probably mix NPT and NPTF, but you'd want to use sealant, since the NPT fitting's threads would still provide spiral leak paths at its root and crest.    They also say not to reuse NPTF fittings, since metal-on-metal galling from the first tightening/loosening cycle may compromise the seal during the next tightening.

[John Ranalletta]

11 minutes ago, Joe Frickin' Friday said:

From this page:

 

 

 

It looks like you could probably mix NPT and NPTF, but you'd want to use sealant, since the NPT fitting's threads would still provide spiral leak paths at its root and crest.    They also say not to reuse NPTF fittings, since metal-on-metal galling from the first tightening/loosening cycle may compromise the seal during the next tightening.

Thanks.  Hopefully, I'll never have to unscrew this connection.  The connection is holding air w/o sealant.  I'll test again with the m/c on board.  If I see tiny leaks, I'll Teflon it.

[John Ranalletta]

1 hour ago, John Ranalletta said:

Thanks.  Hopefully, I'll never have to unscrew this connection.  The connection is holding air w/o sealant.  I'll test again with the m/c on board.  If I see tiny leaks, I'll Teflon it.

It leaked.  Reassembled with Teflon and working as designed.

 

Some testing to go.  Air seems to be holding at a table height of 34.5".  The new bag can go higher but it isn't required.  Here's my assistant turning letters, errr.. holding the m/c in case it should fall.  Quite a gal!

 

If someone wanted to preorder raw steel parts, air spring and hardware, likely this would be a 30 hr job given one had a drill press, more smarts than moi, can weld a bit and the desire.

 

Fini' (at least until I hear a crash from the garage).

 

   

 

 

[Joe Frickin' Friday]

17 minutes ago, John Ranalletta said:

It leaked.  Reassembled with Teflon and working as designed.

 

Some testing to go.  Air seems to be holding at a table height of 34.5".  The new bag can go higher but it isn't required.  Here's my assistant turning letters, errr.. holding the m/c in case it should fall.  Quite a gal!

 

If someone wanted to preorder raw steel parts, air spring and hardware, likely this would be a 30 hr job given one had a drill press, more smarts than moi, can weld a bit and the desire.

 

Fini' (at least until I hear a crash from the garage).

 

   

 

 

 

The outriggers and straps are a nice touch.  Years ago when I was replacing the crankshaft rear main seal on my R1100RT, I had the rear wheel, swingarm, driveshaft, and gearbox all removed.  With all of that weight missing, I went to torque the flywheel bolts and damn near tipped the bike over.  Straps and outriggers like you've got on your lift would have saved me from that close call.

[John Ranalletta]

Thanks.  I have side boards that are not installed that are held on by the outriggers. They're in the photo standing against the doors.  Decided to leave them off for the spring test.

 

 

A side story:  the RT needed oil/filter service prior to START.  I waited for the fittings to arrive because I wanted to do the initial service using the lift.  Yesterday, Grainger updated the ETA for "later this week" due to vendor material shortages.  This morning, as I was wiping up the few oil drips and putting oil service tools away, Grainger advised the part was ready for pickup.