Alloy porosity

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?

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

Reply to
Retro Futurist ...

Paint them well before the tyres are fitted, they will probably be fine. Testing would cost more than a new wheel.

Reply to
MrCheerful

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.

Reply to
Ramsman

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.

Reply to
Bill

Bill laid this down on his screen :

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.

Reply to
Harry Bloomfield

The annoying thing is that you can't fit an inner tube to the things.

Reply to
Ade

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.

Reply to
MrCheerful

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.

Andy

Reply to
Vir Campestris

+1

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 stamping grounds.

Reply to
newshound

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 acrylic.

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.

Reply to
Peter Hill

+1. I have a very good local tyre place and he knew by the wheel (2007 Audi) that the inner rim had likely corroded slightly and leaked. Cleaned it 6 months ago and it's needed no air in that time.
Reply to
RJH

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.

Reply to
newshound

Alloy wheels are laquered inside to get over this problem.

Reply to
harry

Until the lacquer flakes off (as it did on my 5 year old car). I ended up getting all of the wheels skimmed and re-lacquered.

Reply to
Bob Eager

Well castings can be p porous, and normally they used to be Xrayed to show this up, but I've not heard of it happening later without the start of these issues being there to start with. Seems to be yet another cost cutting method, but really how old are they? brian

Reply to
Brian Gaff

Alloy wheels are generally painted (or coated with something similar to paint). If the paint is damaged where the tyre meets the rim they are more likely to leak. As they will often corrode where the paint is damaged.

Reply to
Dave Plowman (News)

Why not?

Reply to
Michael Chare

I have some that got scratched by some weights that were crimped around the rim, instead of glued, like they seem to be now; and this is where they have corroded and now leak slowly.

Reply to
Dan S. MacAbre

Just the usual meja bollocks. If alloy really did go porous, your engine would soon be scrap. Given pistons are made of alloy and have been for many a year as is much else on a modern engine. And the pressure inside a cylinder is far higher than in a tyre.

If a steel wheel is rusty where the tyre meets it, that will leak too.

Reply to
Dave Plowman (News)

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