Alloy porosity

ISTR way back when I was a lad, that some Norton crankcases were found to be porous. They had to paint the inside with something-or-other to stop them leaking.

While I may actually agree with the gist of your argument how many tyres are repressurized a thousand or more times a minute.

G.Harman

With alloy engine parts, the holes/pores soon block with dirt/carbon particles. In any event any leakage is made up in the next fraction of a second. Which doesn't happen with wheels.

You have carbon/dirt in your cooling system? In which case something is porous.

No it doesn't. But I'd love to hear of a wheel which was genuinely porous, rather than just a poor seal between tyre and rim.

And somehow I doubt you've ever changed a tyre yourself.

An immigrant does it for him :)

If my pistons lose 0.1% of the gas on every stroke I won't notice. They are typically running about 25 power strokes a second. If my tyre lost

Andy

How about the cooling system often made of alloy these days. If that were porous, it wouldn't hold pressure.

The tubes of an alloy radiator are wrought and not cast. The process that makes the tubes compacts the alloy, distorts the crystal grain structure and removes (most) porosity.

Casting process can entrain gas and that results porosity. So cast blocks and heads can be porous but drawn tubes and rolled sheet won't be porous. In part the thicker walls of castings prevent porosity as all the holes have to line up and join up for it to leak.

Aero grade alloys for large cast structures (jet engine intercase) are vacuum melted to remove gas and vacuum cast. They can still suffer from strain induced porosity, where voids open up between the crystal grain. Unlike a crack that will go though a grain.

But loads of the rest of the engine, cast. Many engines these days have an alloy block and heads.

I have built cars from the ground up. How a bout you?

That I very much doubt.

Very well, thanks.

Can you see the corrosion if you take the tyre off. i.e. is it obvious to repair.

yes, but I would usually put detergent around the tyre first to confirm the leaking side/area.

I had mine resealed they just spun them on a jig then applied some magic to the milled surface and they were excellent afterwards. 20 quid.

I doubt that is the problem as the tryes need to be leaking to allow ingress.

They seem to use some form of sealer these days. I was having two new tyres fitted to the old car when the fitter took a phone call after applying it to one wheel. And was on the phone for ages. He didn't apply more, and that tyre leaked. The other OK. Had it re-done and it was fine.