Metal Dust Caps

[200h]

today i found i had a puncture,i was going to inflate the tyre so i could get to the tyre bay

unfortunately the metal dust caps had seized on so i couldn't inflate the tyre,

just about got home where i have a full set of spare ct alloys with tyres fitted

i have had to change the wheel so in the morning i can get the puncture repaired.

now i am back on ugly plastic caps as its not going to happen again to me.

[ColinBarber]

A little bit of copper grease on the thread should stop it seizing.

[Wass]

I have never encountered this issue because I check the tyre pressures ( about every other week). I appreciate that some may not have the time or inclination to check tyre pressures and may not have any copper grease to hand. In the past, when needing to lay my hands on a very small quantity of anti corrosive or lubricating oil I use a drop of oil from the engine dip stick. I would use any oil or grease very sparingly on the tyre valve threads to make sure that nothing gets inside the valve itself or reacts with the rubber surface of the valve body.

[rayaans]

Ive had the same metal caps on for 3 years. Never has it seized on my car. Most people tend to put them on way too tight in the fear of them flying off. You only need to tighten them with fingertip force and they wont seize.

Another issue is when people use different materials for dust cap and valve which seems to make them corrode. I dont know the chemistry behind this but it appears aluminium + stainless steel is not a good combination!

[200h]

over the winter time i have checked my pressures especially when the temperatures where dropping so the caps have been off 3 or 4 times this year

the fronts where ok but the rears where solid and wouldn't budge.

i used to check the pressures more often but you get to know how well your tyres keep their pressure and therefore i have checked them less often.

[adnewton]

It pays to check tyre pressures every 1/2 weeks for efficiency. Overtightening is also one of main causes. Finger tighten only ( lightly ). Im on aftermarket caps now - had my originals stolen possibly by some kid for his bike. Use antt-theft ones now.

[matt-c]

Pic of said caps? Most are hex shaped, and often come with a key wrench, but in a pinch any suitably sized spanner or even a pair of pliers will fit

[200h]

i got the caps from kwik fit a while ago the caps where only ever finger tight i.e. screw on until you feel the cap touch the valve stem then tighten 1/16 of a turn only a smidge thats why i was surprised to find the rear caps stuck on.

ah well i have learned a valuable lesson i wont do it again.

[matt-c]

So are they hex shaped? Did you try a spanner/key/pliers?

[200h]

yes they are hex shaped,i tried a spanner,then using pliers holding the valve stem and using the spanner together and they still didn't undo all i found was the valve had stated to spin,so at that point i stopped and hoped i would have enough air left to get me home.

[matt-c]

That's very interesting. I'd be surprised if the caps were anything but aluminium, and of course the valves should be brass, so there should be no way they could rust enough to bind that tightly unless it was steel on steel (and mild at that). My guess is they got cross threaded?

[ColinBarber]

Aluminium and brass react together, especially if water and salt is added.

[200h]

on my other rear wheel i had the same issue (found out on the same day) and i had to hacksaw the cap off it looked like it was brass that had been chrome plated

,the threads would probably be tapped after plating so you would then have brass on brass with a bit of corrosion you probably get the result i've had.

[matt-c]

Aluminium and brass react together, especially if water and salt is added.

They do? Guess I should have paid more attention in chemistry!

[ColinBarber]

When combined with water and road salt, to form an electrolyte, you have galvanic corrosion between the two different metals:

http://en.wikipedia.org/wiki/Galvanic_corrosion

[matt-c]

Well I certainly learned something!

[Pac Man]

By the way you are describing the material of your dust caps I would say that you have had low pressure loss caps fitted at some stage? These are a a big upgrade to the cheap and nasty plastic ones fitted by car manufacturers which allow leakage from the Schrader valve ,unfortunately for them to work correctly they have to fitted over finger tight - but they do work in preventing air loss.

Paul