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Porous wheels

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Laverda Dave:
This is not SOHC related but still has a Honda theme! Actually it’s a request for my 1999 VF800fi so four cams and not one :o

I’ve been having problems with the rear tire losing up to 10psi over 3 or 4 days. I originally put this down to a slow puncture/leaky valve but after changing the tire twice and four new valves later it is still doing it. I have tried everything from using a green anti puncture gloop in the tire to using rim sealer and nothing works. The tire fitter is sure the rim is porous as he has seen this before and especially with Chinese cast bike wheels. I bought the bike with the ‘slow puncture’ four years ago and have lived with it but now it’s become a pia when I use it for trips away.

I have bought a s/h VFR wheel from ebay, it has its original paint and is in excellent condition. The tire fitter has advised I seal the inner rim with anti-porous paint before fitting the tire and new valve just in case this wheel has the same issue.

Can anyone recommend a suitable anti-porous paint, all I can find is garage floor paint and I really don’t need 2.5 litres of the stuff at £50!
I know 1960’s Royal Enfield’s had a problem with porous engine castings and they used to seal the inner halves with a special paint although that was a high temperature paint and I don’t know what that was called either ::)

Any recommendations welcome otherwise I'll have to travel with my air compressor in tow!

Cheers
Dave

K2-K6:
Worthwhile first Dave, that's if you've not already done it that is, lay your faulty wheel and tire on it's side and put a "bead" of soapy water round the rim to watch for bubbles, they can be veeeery slow but will show over 1/2 hour or so. Then flip and do the other side.

I've had to do quite a few car wheels recently and none were porous casting but all leaked through under the paint/lacquer under where the bead sits on the rim. These were corrected with clearing all finish and starting again with etching primer to refinish that area.

McCabe-Thiele (Ted):
10 psi over 3-4 days is a fair leak. Is it feasable to do a water immersion test and rotate the wheel possibly helped by inflating the tyre nearer to the maximum. I have had similar issues on cars over the decades and it's ways turned out to be rim seal due to rim corrosion. I fixed this last time by having the rim stripped & powder coated. I would have expected a porous rim to fix with the gloop stuff the AA use.

Yetanotherbike:
I had a similar leak on my Triumph T595. It turned out to be a minute hairline crack in the valve body. Even with soapy water if was barely bubbling. Luckily my local tyre fitter was on the ball

Oddjob:
Never seen a porous mag wheel in all my years in the trade.

I'd suspect a crack or most likely rim leakage.

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