metal dust caps stuck

sithmaster

up to yet I have heated up with lighter they will not move
then I cut the tops off and put loads of wd40 on the threads left for 30 minutes with 2 pairs of pliers with all my strength they still will not move


the metal is quite thick for a dust cap about 3-4mm


I'm thinking I will just have to renew the valves


never using metal ones again

Ranger8

2 prs or pliers or mole grips.. 1 to hold valve as close to threads as possible to stop it twisting and the other to turn cap.
Worked for me

Richard53

Ranger8 wrote: »

2 prs or pliers or mole grips.. 1 to hold valve as close to threads as possible to stop it twisting and the other to turn cap.
Worked for me

Just about to say exactly this. Two pairs, one to hold and one to turn. It doesn't really matter if you damage the threads of the valve stem slightly, as the stem nut will probably straighten them out as you remove it. Probably a new tube would be a good idea, if it's old enough for the valve cap to corrode.

I like metal valve caps, especialy those with a rubber o-ring. The plastic ones don't look as if they would hold back a good sneeze, but a well-sealed metal one might slow down a failed valve core long enough for you to get somewhere safe.

As for the corrosion issue, if you are removing the caps weekly to check your pressures (as you should), it won't be a problem.

Strider590

Richard53 wrote: »

As for the corrosion issue, if you are removing the caps weekly to check your pressures (as you should), it won't be a problem.

AFAIK, it's not corrosion.... It's a chemical reaction between the alloy cap and the brass valve stem. For all intents and purposes they weld themselves together.

Richard53

Strider590 wrote: »

AFAIK, it's not corrosion.... It's a chemical reaction between the alloy cap and the brass valve stem. For all intents and purposes they weld themselves together.

OK, my bad. I'm no chemist, so I can't say if it is technically corrosion or something else, but I was using the familiar term.

And corrosion is still a chemical reaction, I think.

Strider590

Richard53 wrote: »

OK, my bad. I'm no chemist, so I can't say if it is technically corrosion or something else, but I was using the familiar term.

And corrosion is still a chemical reaction, I think.

Yes technically it is

However corrosion requires an external element and as such would only affect a small area, ie the first few mm of thread. But the reason these get so stuck is that the brass reacts with the alloy and literally welds the entire thread without the help of any external elements.

reeac

Strider590 wrote: »

AFAIK, it's not corrosion.... It's a chemical reaction between the alloy cap and the brass valve stem. For all intents and purposes they weld themselves together.

Corrosion is often described as a chemical reaction in the wrong place just as a weed is a plant in the wrong place.

Prothet_of_Doom

Strider590 wrote: »

AFAIK, it's not corrosion.... It's a chemical reaction between the alloy cap and the brass valve stem. For all intents and purposes they weld themselves together.

Technically it's corrosion. :cool::D An electronlytic reaction, causing corrosion that welds them together. Semantics. the result is the same PITA.

I had this and used 2 pairs of mole grips.

Richard53

Thus proving an important point:

The technicalities don't matter. Duct tape, WD-40, Mole grips and cable ties will fix anything.

londonTiger

worse case scenario, valve stems are disposable - though getting a wheel of a bike is probably a PITA compared to a car.

if a valve cap has seized onto the stem, it would mean the stem is a little damaged too and won't seal properly to a new cap.so dont be shy with about damaging it.

I would just use two mole grips and unscrew them apart. wd40 is not a penetrating oil, a proper penetrating oil will go up deeper into the corrosion than a wd40.