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?
That's just happened to me, 57 plate Zafira with 61k miles. NSR very
slow leak, taking a couple of weeks to lose more than a few psi. Fixed
at the local tyre place by cleaning the rim and applying fresh sealer.
Two months ago; so far, so good.
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.
*If Barbie is so popular, why do you have to buy her friends? *
Dave Plowman email@example.com London SW
When you say paint, what with and inside or outside the wheel? Or is
this referring to painting the edges, or more, with sealant.
Sorry if this is a stupid question, but I'm just learning how little I
know about wheels and tyres.
No point to adding it to the outside, it needs to be inside. The
problem with alloy rims, is that the salt and water corrodes the alloy,
causing a poor seal to develop between tyre and wheel rim. The
corrosion needs to be cleaned off down to bare metal, then the bare
metal painted to protect it.
There are plenty of places that will refurbish wheels to better than
new, but it is not cheap and takes a few days or so. One of my
customers had his Lexus wheels refurbed because they leaked extensively
and they were fine afterwards, iirc it was about 200 for all five.
For my wheels I strip the tyre, clean the inner rim up, and use a belt
sander on the important seal area around the edge, then spray them with
etch primer, then some silver wheel paint, works fine, even if you miss
out the etch primer.
Mine were done by Toyota on a recall when the car was a year or so old.
They lasted over 10 years, and then started to leak on the rims. I had
them redone, and they are bubbling in places only 4 years later.
When I was at university, my father used to edit the magazine "Paint
Technology". I used to write all my exam revision notes on his galley
proofs (fan-fold paper, about 5 inches wide, very convenient for
summarising key points). Towards the end of my professional career, I
found myself approving contracts placed with the Paint Research
Association at Teddington, which had been one of his very regular
Porosity is something that will have been there from manufacture. Over
time the pores can open up and then it leaks.
Cylinder head would have to be removed and pressure tested. Though just
running something like steel seal will cure most pinholes.
Wheels you will never find the pore, just paint the inside of the rim.
It seems that epoxy is not longer considered to be best but some sort of
Royal Enfield couldn't cast a non-porous crankcase with integral oil
tank for the 250 Crusader to save their lives. They all had yellow paint
on the inside to stop the oil leaking out.
I think the cylinder problem and the wheel problem are different. Alloy
wheels are normally varnished or painted to prevent corrosion. But
flexing of the tyre against the seat area can remove the coating. The
crevice between the tyre and the rim is then more liable to corrosion
from water and, especially, salt during the winter. The alloy becomes
pitted, leaving a leak path. The greasy lubricant used when new tyres
are fitted can help prevent this, but once you have pits the only real
solution is to to remove them by abrasion, and to "paint" the metal
surface to prevent further corrosion before the tyre is re-fitted.
Decent tyre suppliers should be able to sort this out.
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