Important Warning about valve stem caps! - Chicagoland Sportbikes
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post #1 of 16 (permalink) Old 04-22-2006, 11:43 AM Thread Starter
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Important Warning about valve stem caps!

I'm not sure if this is what caused my problem or not, but it's worth a warning to those that ride the track, or other high speed "areas". Sorry for the length, but you need to have the image of the day to get the full effect.

I attended the Learning Curves Racing license school yesterday (4/21). After already completing two full NESBA days at Road America and getting bumped to Intermediate, I was very confident in my abilities there compared to those in the class that had not ridden the track before.

Woke up early, took a shower, got the bike ready, and everything was going perfect as the sun was coming up. Finally found the LCR pit area, got in class, everyone is pumped up because it is a beautiful day. First class session is over and we're getting ready for our first practice session.

I check the tire pressure. Front 31 -check, Rear 25 -hmmm? I roll the bike over to get some air from a neighboring pit...nice guys from New Jersey. Rear 30 -check. Cool, now I'm ready to rock. First call for LCR...gear on, bike started, off the stand, and out to Pit-In.

We go out for our snail pace lap to show the new guys the track. No biggie...it's a beautiful 4 mile scenic trip. 2nd lap, Rick is waving us by two at a time. I get my wave on the carousel and motor around...remembering I don't have a lot of heat in my tires yet. I take it easy until I get back to turn 1, and then it's GAME ON. I pass one rider going into T-3, then another two down the straight to T-5. Now...this is where it all goes wrong...

Breaking hard and downshift for T-5, lean it in, a little squirmy...hmmm, roll on to drive out...REALLY squirmy...thinking maybe I picked up some sand or ran through something. I take it a little easier into T-6 but now it's even worse...can barely steer the bike out of the turn. My hand comes up and I'm riding the edge of the track at about 30mph trying to figure this shit out. I do the next 2 miles of the track at about 15 mph waving anyone behind me by hoping I don't get rammed by another student.

I finally get back to the pits, and up on the rear stand. Glove get thrown into the tent as well as the jacket and back protector. The Arai got gently placed in the chair.

My rear tire is completely flat...not one bit of air. You can almost push the tread all the way to the rim. The tire was so hot you could hardley touch it. I'm pissed. Get the tire off and go to get a new one. Dunlop brought the wrong tires due to a sticker error. Michellin has a tire...cool. Power Race - Medium/Soft

I go back to class...fuckin tight schedule. Get out of class, pick up my tire. The guy didn't look for a puncture. The tire was scorched anyway. Get the tire back on the bike. Check the pressure - 22 psi...good to go. That's when I notice my valve stem cap from the original tire sitting next to my stand. This had no meening until later...

Later on I realized that the only reason the original stem cap was there, was because I had NOT put it back on after getting the first tire some more air. I never removed it after the flat, because I new there wasn't any pressure in the tire.

The centrifugal force at the high speeds of the track were "probably" enough to pull the valve core in, and therefore, allowed the air in the my tire to escape because I DID NOT have the o-ring valve cap on as required by tech. It was on when I went through tech, so it is not their fault. It is my fault for allowing myself to get in a hurry and overlook a simple detail that could have had a far worse outcome than just the cost of a new tire.

I'm almost ashamed to admit all of this, but hopefully it will help prevent anyone else from experiencing this same ordeal.

PLEASE: Check you caps, and make sure they're on and tight.

BTW...The Michellin Power Race tires...

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STT "A" 130
Track: 2006 GSXR-750
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post #2 of 16 (permalink) Old 04-22-2006, 11:50 AM
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i have never seen a valve stem open due to rotating force, but hey, good job keeping it up and getting off the track in a safe manner.

i did LCR last year.. good stuff

-Mopar

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post #3 of 16 (permalink) Old 04-22-2006, 12:07 PM
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Maybe I'm still hung over, but the forces on the valve stem would actually push the seal closed if they effected it in anyway. And those o-rings caps, if given a release of 20+ psi would probably just stretch and pop-off the threads.

You probably just had puncture in the tire or some other leak.

Jeff
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post #4 of 16 (permalink) Old 04-22-2006, 12:08 PM Thread Starter
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I could have run over something, but the cap seemed to be the most likely cause. Especially since tech requires caps with o-ring seals. Hell...honestly, I don't know why it went flat.

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post #5 of 16 (permalink) Old 04-22-2006, 12:09 PM Thread Starter
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Quote:
Originally Posted by shadrach
Maybe I'm still hung over, but the forces on the valve stem would actually push the seal closed if they effected it in anyway.

You probably just had puncture in the tire or some other leak.
The core is pushed towards the outside of a tire to let the air out. Centrifugal force would act on that same part in the same direction.

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STT "A" 130
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post #6 of 16 (permalink) Old 04-22-2006, 12:27 PM
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Quote:
Originally Posted by stkr
The core is pushed towards the outside of a tire to let the air out. Centrifugal force would act on that same part in the same direction.
???



The seal in the core pushes against a seat. Forces from the compressed air (and minimally from the spring that holds the stem in place) would push the seal closed even harder. In fact, there are valves used on some moutain bikes that have no spring in them at all. With little to no air pressure behind them, the stem will just float freely, allowing the rider to easily and completely deflate the tires for storage and transporation of the bike.

There is no way to increasing air pressure would ever create a leak in the valve, as the more pressure, the harder it would push the seal closed.

Air is let out of the valve by pushing the stem INTO the tire. The core is screwed into the tire and doesn't move, only the stem moves inward. "Centripetal" force would not pull the stem inward.

Jeff
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Last edited by shadrach; 04-22-2006 at 12:33 PM.
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post #7 of 16 (permalink) Old 04-22-2006, 12:38 PM
 
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Quote:
Originally Posted by shadrach

Air is let out of the valve by pushing the stem INTO the tire.
So, the same direction that centrifugal force would exert on a straight stem?
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post #8 of 16 (permalink) Old 04-22-2006, 04:00 PM
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Quote:
Originally Posted by shadrach
???

In fact, there are valves used on some moutain bikes that have no spring in them at all. With little to no air pressure behind them, the stem will just float freely, allowing the rider to easily and completely deflate the tires for storage and transporation of the bike.
Those are presta valves, not schrader valves that are used on cars/trucks and motorcycles.

Schraders CAN open up slightly under extreme rotational force. Enough to let air out a little at a time. Even plastic valve stem caps wont blow off the threads at 60psi (which is more than you put in your F3's tire). I've tried (practical joke on former supervisor's company truck). Also if the core isnt screwed all the way in its more likely to do this. Dealt with conversion trucks with similar issues. No nails, bead is good, stem was good but the cap bubbled the soap water on the balancer.
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post #9 of 16 (permalink) Old 04-24-2006, 07:20 AM Thread Starter
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Okay...the more I think about it, it probably was just something I ran over, but it's just an ironic coincidence that I had left my valve cap off during that session.

Either way, I learned that you cannot get complacent at the track and just assume that everything is fine like the last session.

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post #10 of 16 (permalink) Old 04-24-2006, 08:02 AM
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maybe it's a bad stem or you have a rim leak.

<--------Sticky Nicky
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post #11 of 16 (permalink) Old 04-24-2006, 08:04 AM
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Wow.....Good heads up on your part for getting off the track....SAFELY!!

Seriously though i do not really think you lost the air through the valve due to the G's. Like said more than likely a puncture or even the valve itself coming loose. (screw shrader right?)

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post #12 of 16 (permalink) Old 04-24-2006, 08:36 AM
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I know it was a pain in the ass and misforturne for you. But you did learn something and you will never make that mistake again. You also kept the bike on 2 wheels and demonstrated your adaptation to crazy things that can happen when in a racing situation.

If I were you I would be proud!

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post #13 of 16 (permalink) Old 04-24-2006, 09:26 AM Thread Starter
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Thanks Yup...there was some serious pucker factory going on going through T-5 The worst part was trying to make it 2 miles back to T-14 pit road at 10 mph wondering who was not going to see me and hit me from behind. I had my hand up AND my leg out just in case

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post #14 of 16 (permalink) Old 04-24-2006, 09:30 AM
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Quote:
Originally Posted by stkr
Thanks Yup...there was some serious pucker factory going on going through T-5 The worst part was trying to make it 2 miles back to T-14 pit road at 10 mph wondering who was not going to see me and hit me from behind. I had my hand up AND my leg out just in case
There's a lot of places to get off that race track.

On the inside of 8 you can get through the fence. And if you wanted to you can always just go to the nearest corner worker, lean your bike up against the wall and request a crash truck to bring you back.

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post #15 of 16 (permalink) Old 04-24-2006, 10:02 AM
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Real question is..did you get your race license?

I'll admit, once I check the pressure in the morning I tend to forget about it. Other than visual inspection, you really can't check tire pressure after they are nice and hot. But you can still go over everything else afterwards (brakes, oil, etc.)

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post #16 of 16 (permalink) Old 04-24-2006, 11:16 AM Thread Starter
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Yes...I got my diploma, so all I have to do is pay "another" $110 to get my license.

After the practice session, I went to get a new rear tire, but the Dunlop trailer brought the wrong tires. They had 180 stickers on 190 tires I ended up going to the Michelin trailer and got a nice Power Race-Medium. When I get some more money, I'll probably get a power race front also.

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STT "A" 130
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