Author Topic: Porous wheels  (Read 1059 times)

Offline Laverda Dave

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Porous wheels
« on: June 11, 2022, 11:22:36 AM »
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
1976 Honda 400/4
1977 Rickman Honda CR750
1999 Honda VFR 800FX
1955 750 Dresda Triton
1978 Moto Morini 350 Sport
1978 Honda CB400/4 'Rat' bike
1982 Laverda 120 Jota

Offline K2-K6

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Re: Porous wheels
« Reply #1 on: June 11, 2022, 12:22:24 PM »
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.

Offline McCabe-Thiele (Ted)

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Re: Porous wheels
« Reply #2 on: June 11, 2022, 12:23:08 PM »
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.
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Offline Yetanotherbike

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Re: Porous wheels
« Reply #3 on: June 11, 2022, 12:50:08 PM »
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

Offline Oddjob

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Re: Porous wheels
« Reply #4 on: June 11, 2022, 12:57:00 PM »
Never seen a porous mag wheel in all my years in the trade.

I'd suspect a crack or most likely rim leakage.
Kids in a the back seat cause accidents.
Accidents in the back seat cause kids.

Offline Laverda Dave

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Re: Porous wheels
« Reply #5 on: June 11, 2022, 05:59:22 PM »
From what you have all said it sounds like potential rim leakage. This is strange though as I have checked the rim and all appears to be fine, no dings or cracks either. The tire fitter (he's actually an ace mechanic, used him for 25+ years) also checked the rim inside and out and he could find nothing wrong BUT he did say only slight damage would cause a leak at the pressure involved. The green gloop did slow it down but did not eliminate it so maybe it is the critical area between the rim and the tire that is slightly damaged.

Nigel & Ted, yep, I did the soapy water test a couple of times and could find nothing on the rim but there was a very, very slight weep on the valve head, bubbles took over 30 minutes to show but they were tiny. Anyway I replaced the valve (twice) and the problem is still there.

I will install the new rim with my new tire and see how it goes. I won't use the paint, Honda never did so if all is fine it will point to the old wheel being damaged and fit for the bin.

Thanks for all the replies.
1976 Honda 400/4
1977 Rickman Honda CR750
1999 Honda VFR 800FX
1955 750 Dresda Triton
1978 Moto Morini 350 Sport
1978 Honda CB400/4 'Rat' bike
1982 Laverda 120 Jota

Offline robvangulik

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Re: Porous wheels
« Reply #6 on: June 13, 2022, 02:55:03 PM »
Like Ted said, hold the complete wheel under water and it WILL show where it leaks!
Even a very small inflatable childs swimming pool works, and doesn't cost you any real money.

Offline Trigger

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Re: Porous wheels
« Reply #7 on: June 14, 2022, 07:52:39 AM »
Have had to have lots of alloy wheels powder coated due to rim leaks over the years.
If you put a innertube in and it doesn't go down, you know it is the wheel  ;)

 

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