i have a silly dust cap problem

[warrenhewitt10]

my mates bike has its mot 2morro and the back tyre pressure is very very low, we tried to take the cap off and its well and truely stuck on....

http://file050a.bebo.com/20/original/2010/01/25/23/15062929a12141528636o.jpg

any ideas?? lol

weve tried mole grips and pliers to hold the bottom but dont want to try too hard for fear of wrecking the valve

[simesb]

Tried heating it a little with a lighter (it looks like a metal cap)

[warrenhewitt10]

we had a hairdryer on it for a good while but no luck :( a lighter would be alot hotter tho i suppose

[Sid Squid]

You're not alone in this - aluminium caps are well known for corroding in place.

Try a few sharp taps on the end of the cap to shock the threads, it's awkward as you need to hit it squarely on the end, and of course the hub is in the way, but it's worked a few times. Otherwise as the cap is aluminium and very soft in one stubborn case I managed to cut the cap off.

[barwel1992]

why not hold the bottom with pliers and the top with the grips and twist the top? or is that what you ment when you sead grips on the bottom

[warrenhewitt10]

why not hold the bottom with pliers and the top with the grips and twist the top? or is that what you ment when you sead grips on the bottom
yeh i tried that but it still didnt budge! didnt want to grip it too hard incase it splits!

does anyone know if a bike can fail the mot because of tyre pressure?

[barwel1992]

not sure but im sure they would try and pump it up if it was flat, so you could just see if they get it off when it goes in for the mot

[beabert]

we had a hairdryer on it for a good while but no luck :( a lighter would be alot hotter tho i suppose

what about curling tongs?

[7755matt]

Its not a reason to fail the MOT, however the tester is entitledto refuse to test the bike if he thinks the tyre is too flat to be able to safely test it

[The Guru]

Tried soaking it with WD of 4in1 spray?? Obviously try not get to much on the tyre

[fastdruid]

Boiling water, far less chance of melting the rubber, bubbling the paint or burning your finger...

Druid

[fastdruid]

Tried soaking it with WD of 4in1 spray?? Obviously try not get to much on the tyre

<repeating self>
Use plusgas or similar not WD40, WD40 while better than nothing is *NOT* a penatrent.
</repeating self>

See this table originally from "Machinist Workshop" but copied from http://bbs.homeshopmachinist.net/showthread.php?t=27429

Penetrating oil . Average load .. Price per fluid ounce
None ................. 516 pounds .
WD-40 .............. 238 pounds .. $0.25
PB Blaster ......... 214 pounds .. $0.35
Liquid Wrench ... 127 pounds .. $0.21
Kano Kroil ........ 106 pounds .. $0.75
ATF-Acetone mix.. 53 pounds .. $0.10

Druid

[yorkie_chris]

ATF and acetone ehhhh

[ophic]

I had this problem with an oxford aluminium cap. You can't get too much twisting force on the cap because the mounting is rubber and just deforms. In the end I used 2 sets of long handled pliers, one on the rubber and one on the cap, and I used such force that I thought I'd wreck the valve. Fortunately it's fine.

[Taipan]

Take the wheel off. Cut the valve off. Break the bead and put a new valve in. Or take the wheel to a tyre place and get them to do it. Wont cost much but riding with a flat tyre could cost you dearly.

[renman8957]

Got a new valve put in this morning, only way really, cost £15 and didn't take long, and passed its MOT. Thanks for the help guys, as always much appreciated

[yorkie_chris]

And don't forget to bitchslap whoever put such tacky chavness on there :-P

[renman8957]

haha, yes now I know not to do it again, stick to the bicycle style standard black plastic jobbies

[The Guru]

<repeating self>
Use plusgas or similar not WD40, WD40 while better than nothing is *NOT* a penatrent.
</repeating self>



You'd only be repeating it if I had read any of you previous posts... which I've not and I never said it was a penetrant. :rolleyes:

[fastdruid]

I never said it was a penetrant. :rolleyes:

Then why use (or rather suggest the OP uses) it? Apart from obviously the smell. ;)

Druid

[The Guru]

Because its probably got a better chance than boiling water

[ophic]

Penetrating oil . Average load .. Price per fluid ounce
None ................. 516 pounds .
WD-40 .............. 238 pounds .. $0.25

surely that's gotta be why.

[fastdruid]

Because its probably got a better chance than boiling water

Boiling water will cause the cap to expand[1], ideally expanding enough to free off what is presumably the corrosion attaching it to the stem. Using a naked flame is either asking to be burnt, set fire to the stem, blister the paint or all three. WD40 as previously stated is *not* a penetrant so will do virtually nothing unless there was little wrong in the first place. BTW that test was after *soaking* the parts for 8 *hours*.

Druid

[1] I'm not sure what the metal the thread on the valve is made from but I presume either steel or maybe brass, both of which have a lower Coefficient of Thermal Expansion[1] than Aluminium - http://en.wikipedia.org/wiki/Coefficient_of_thermal_expansion

[Dicky Ticker]

Looking at the picture it seems to be cross threaded-----let the tyre down, break the rim seal, cut the old valve off and fit a new one and blow the tyre back up to the proper pressure.
Apart from the MOT Examiner being able to refuse it is dangerous to ride if it is so under inflated that you are worried about it passing the MOT.

[The Guru]

Virtually nothing or nothing? There is a difference.

And yes tyre valves are typically made out of *Brass*

[GOZA]

ive seen people loctiting these on so they cant be nicked bit stupid because then you can get the proplem uve got. proberly have to get the valve changed

[independentphoto]

And don't forget to bitchslap whoever put such tacky chavness on there :-P

Strange that. It is possible to get those in black too and Bridgestone actually recommend metal caps with o-rings because UNDER LOAD (i.e. riding), a trye can go down very quickly without a cap fitted.

That's what the man says and he knows better than I. Don't fancy doing a test either before some wisearse suggests it.

Garry
:cool:

[renman8957]

wasn't cross-threaded, was just corroded in place, new valve on it and MOT passed

[Holdup]

At least when its stuck on no one can nick them :p

[warrenhewitt10]

At least when its stuck on no one can nick them :p

i had some nice dust caps that even said SV650 on the top and then i went to portrush for the nw200 and came back to the bike and they wer gone........gurrr

[ophic]

[1] I'm not sure what the metal the thread on the valve is made from but I presume either steel or maybe brass, both of which have a lower Coefficient of Thermal Expansion[1] than Aluminium - http://en.wikipedia.org/wiki/Coefficient_of_thermal_expansion
Could this be a contributory factor? We all know aluminium and steel tend to corrode each other, but the threads must be made of something relatively corrosion resistant. Could it be just that the cap was put on in summer and now the weather is colder, it's contracted?

[yorkie_chris]

Strange that. It is possible to get those in black too and Bridgestone actually recommend metal caps with o-rings because UNDER LOAD (i.e. riding), a trye can go down very quickly without a cap fitted.

That's what the man says and he knows better than I. Don't fancy doing a test either before some wisearse suggests it.

Garry
:cool:

Metal caps with O rings in some racing rules. BUT racers aren't so frigging stupid as to leave them in place so long they seize. Bridgestone man is talking out of his 'arris though. Pretty much all new bikes have got plastic valve caps on. You think they would mess with liability?

Fair enough no cap at all isn't good, but that's not the arguement here.

Test? Easy. I send you a valve core, you weigh the moving spindle. Test how much force is required to move the valve against air at 40psi (or whatever hot pressure you end up with). F = mv^2 /r if first F you got is bigger than second one, you going to die. Simples.

Chav dustcaps on a roadbike are utterly pointless, there's bugger all wrong with plastic ones. Plus they come free with valves that are 12p each so there's no excuse for not fitting a fresh 'un with every tyre.