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Flat tire number two! :-(

PandaCub

Active Member
I posted earlier about a flat main on my -14A where lack of tire talc caused the debossed area of the tire to chaff a remarkably similar pattern on the inner tube (photos 1 and 2).

Well, while doing routine maintenance yesterday I noticed the valve stem cap was missing from my Beringer nosewheel, so I put on a cap from an old tire, reinstalled the wheel fairing, and thought nothing more of it.

This morning as I started to roll the -14A out of the hangar I heard two scrape sounds (in as many wheel revolutions) and thought this can't be good. I began to push the airplane back into the hangar for inspection, only to hear the dreaded psshhhhh from the nosewheel. It was flat within 10 seconds and later examination showed a sheared-off valve stem (photos 3 & 4). No flying today!

Are clearances so tight between the valve tip and nosegear brackets that you can't install a valve stem cap? I really don't like operating with exposed valve stems. Maybe a low-profile plastic one will work - and I'll definitely try the spin test while it's on the jack - but those yellow metal caps are evidently a no-go with my setup. Wonder if one of my wheel fairing screws is too long? I'm scratching my head here (as I await shipment of new valve stems).
 

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Yup. I can't put a cap on my nose wheel either. Seems to be a common problem with the Vans nose wheel fork. I just replaced my tire and tube after adding air to my nose wheel resulted in a flat tire in my hangar. I'm sure that junk got into the Schrader valve and that caused the leak but having been stranded away from home on a weekend with a flat nose tire I don't mess around.

-Marc
 
I have the Beringer nose wheel on my -14A and have no problems with the valve cap; however, the cap is not the yellow type but black that came with the wheel. Next time I have the fairing open I will take a look at clearances with the fork.

Yep, true with most of Van's front forks, minimal clearance to the stem and the large yellow caps will hit, no cap or the black plastic is the one to use.
 
Clearances

.062 is the clearance with the plastic cap on and .188 with the cap off for the Beringer nose wheel rim to fork.
 
Many thanks to all for the replies.

Just goes to show how you can't take anything for granted with regard our airplanes: e.g. I innocently screwed a yellow Michelin Airstop valve cap onto an uncapped nosewheel stem and it ended up grounding me for 5+ days while I wait on the U.S. Snail to deliver new parts. Good thing I'm at home base and don't really need to fly anywhere! Live and learn :)

I located some low-profile metal valve caps that I'll try out before I put the nosewheel fairing back on. The standard plastic caps measure out at 13mm. These are a couple millimeters shorter:
 

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I've had a similar issue crop up recently. I have the Grove tubeless nosewheel on my 6A and have had 2 valve stems shear apart on landing in the past month. Both times I had the yellow cap installed on the valve, which seems to have impacted the fork and bent the valve stem. Prior to these 2 recent incidents I had been flying the plane for 2 years with the same setup and never had an issue (and the previous owner flew for years without issue as well). I've checked that all bolts on the hub and axle are properly tightened, I've measured the clearances from all angles, I've confirmed that the fork is straight, I've compared the measurements of the fork to the original builder's plans, I've made sure the nosewheel spins straight and doesn't move side to side...everything checks out perfectly. I asked the manufacturer (Grove) if they have seen this issue before and they said "never".

Does anyone have any ideas of what may have changed that would cause this to suddenly become an issue?

I'm now running with just a black automobile dust cap instead of the yellow cap so that there's more clearance, and also carrying a spare valve stem in my plane, but I am very curious as to why this would only become an issue after many years.
 
Are clearances so tight between the valve tip and nosegear brackets that you can't install a valve stem cap? I really don't like operating with exposed valve stems. Maybe a low-profile plastic one will work - and I'll definitely try the spin test while it's on the jack - but those yellow metal caps are evidently a no-go with my setup. Wonder if one of my wheel fairing screws is too long? I'm scratching my head here (as I await shipment of new valve stems).
That right-most photo when zoomed in... It certainly looks like something has been chewing away at the side of the tire. Are your screws holding the wheelpants on too long? I'm amazed it was holding air.
 
That right-most photo when zoomed in... It certainly looks like something has been chewing away at the side of the tire. Are your screws holding the wheelpants on too long? I'm amazed it was holding air.

I saw those marks and thought it was just the flat nose wheel scrubbing on the concrete when he was pushing the plane back in the hanger.
 
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