On Sunday, 1 October 2017 19:23:23 UTC+1, Retro Futurist ... wrote:
"Bill" wrote in message
...
I may be about to buy, from a scrapyard, a set of 5 replacement wheels for
the recently purchased car to get a spare wheel, proper sized tyres and
wheels that fit the wheel nuts.

In the past, I've often been told that the reason for a slow puncture was
that the alloy wheels had gone porous.
More recently, I've been told that the cylinder head on a certain vehicle
had gone porous and that was why it chuffed when cold.

I have always wondered whether this is a standard get-rid-of-him phrase
taught as part of the Car Mechanics PhD (Hons) course, or whether alloy
does actually start to leak.

Does anyone know? Is there any sort of standard test, like wheel tapping,
that can detect this sort of rot?

I have found them to leak and the seal goes at the rim ......

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.