C2 wheel porosity......

**Tracy C.** · December 13, 2006, 04:40 PM

Re: C2 wheel porosity......

Bill,

I'm not making the same connection as you with regard to enlarged valve stem holes. I believe an intertube stem would fit through a regular sized valve stem hole just fine. (I don't know why anyone would enlarge the holes)

I'd put a set of tires on them and see how they hold air before coating them them with anything.

good luck,
tc

**Wayne K.** · December 13, 2006, 05:17 PM

Re: C2 wheel porosity......

Bill,

As a rule I think that an alloy wheel has a tendency to lose air over time more so than a steel wheel. It could be that whoever installed the tubes just didn't like that characteristic. I also remember some customers when I worked in a service station in the 60's that insisted that we put tubes in tubeless tires because they thought that was safer. As Tracy has suggested it just might be that there is nothing wrong with the wheels unless you know for sure differently. We never had to change the hole size to install tubes in any wheels that we put tubes in.

Wayne

**John Daly** · December 13, 2006, 05:41 PM

Re: C2 wheel porosity

Here's the repair procedure from the General:
Aluminum Wheel Porosity Repair
1-Remove the tire and wheel. Refer to Tire and Wheel Removal and Installation .

2-Inflate the tire to the manufactures specified pressure as stated on the tire.

3-Submerge the tire/wheel into a water bath in order to locate the leak.

4-Inscribe a mark on the wheel in order to indicate the leak areas.

5-Inscribe a mark on the tire at the valve stem in order to indicate the orientation of the tire to the wheel.

6-Remove the tire from the wheel. Refer to Tire Mounting and Dismounting .
Important: Do not damage the exterior surface of the wheel.

7-Use number 80 grit sandpaper to scuff the inside of the rim surface at the leak area.

8-Use general purpose cleaner such as 3M®, P/N 08984 or equivalent, to clean the leak area.

9-Apply 3 mm (0.12 in) thick layer of adhesive/sealant, GM P/N 12378478 (Canadian P/N 88900041) or equivalent, to the leak area.

10-Allow for the adhesive/sealant to dry.

Align the inscribed mark on the tire with the valve stem on the wheel.

11-Install the tire to the wheel. Refer to Tire Mounting and Dismounting .
Pressurize the tire to 276 kPa (40 psi).

12-Submerge the tire/wheel into a water bath in order ensure the leak is sealed.

13-Inflate the tire to the specified pressure as stated on the tire placard.

14-Balance the tire and wheel. Refer to Tire and Wheel Assembly Balancing - Off Vehicle .

15-Install the tire and wheel. Refer to Tire and Wheel Removal and Installation .

**Bill W.** · December 13, 2006, 05:49 PM

Re: C2 wheel porosity......

Tracy/Wayne, You may be right, I have not mounted a tire to test these wheels ability to hold air. The only way I can account for the enlarged holes is by someone adding tubes. The owner does remember some problems with these wheels, but isn't sure what was done to them. They have been off the car for many years.
Bill

**Bill W.** · December 13, 2006, 05:55 PM

Re: C2 wheel porosity

John, I was not aware the General had a repair kit for porosity problems. Thanks for posting this! Unless someone comes up with a better solution, I think my next move is to test these wheels and apply GM's sealant as needed. Bill

**Michael H.** · December 13, 2006, 06:08 PM

Re: C2 wheel porosity......

Bill,

Many years ago, I learned about what was supposedly the first 64 to roll off the assy line with KO wheels. I don't remember the owners name at the moment but I'm sure others will remember. He purchased a silver blue FI coupe with KO wheels. The dealer eventually informed him that the order was being held up because of the wheels. The problem was indeed porous castings. Somehow, he was able to have the order pushed through and the car was delivered with the KO wheels but, according to the owner, left the plant with tubes installed in all five tires. This car is a very low mileage one owner that was shown at the Bloomington Gold event years ago. Still had the original wheels and tires on it when I judged it. (some time in the early 80's) If I remember correctly, there was paperwork to support his claim. I think his name was Alan and he probably still has the car to this day. Lives in central Illinois?

Not sure about this but I seem to remember that tubes for 15" tires had the large size stem which would have required larger holes in the AL wheel?

**Mike McKown** · December 13, 2006, 07:39 PM

How many points deduct for tubes? *NM*

**Michael H.** · December 13, 2006, 08:11 PM

Re: How many points deduct for tubes?

Interesting question. I really don't know because I would have been the engine/compartment judge at that time. Now that you mention it, I have to wonder if the tubes were ever seen and points deducted?

**Christopher R.** · December 13, 2006, 08:58 PM

Re: C2 wheel porosity......

Common problem in the aerospace industry. See MIL-STD-276. Your tax dollars at work. This may be too much for this problem. Ask tire and wheel places.

**Mike McKown** · December 13, 2006, 09:23 PM

We used to use a product available through

Rotunda (Ford). It was a two part epoxy probably much like JB Weld. It's purpose was to seal porous automatic transmission cases. I dont' know why something like that wouldn't work. The problem would be finding the leak if it was tiny.

**Mike McKown** · December 13, 2006, 09:27 PM

I've never used them but it seems

the valve stems that are held in place on the back side with a threaded nut have a larger hole than a standard tubeless stem. Could this be it? Maybe he had problems with the stems sealing. There are different diameter tubeless stems also.

**Wayne P.** · December 13, 2006, 09:58 PM

Re: I've never used them but it seems

If you don't want to smear epoxy all over the place and you only have a few small holes, here is the easy, clean fix. When you locate the leak, just peen it with a sharp punch. I've done this many times on newer model aluminum wheels and it always worked.

**Jimmy G.** · December 13, 2006, 10:34 PM

Re: C2 wheel porosity......

Call John Ballard. He can recommend a coating (paint) to seal the aluminum. It should be a simple process just like sealing a basement wall from water leaks. I would think a high build epoxy priner should work to solve this problem. Ask John 502-426-2184.

**Bill W.** · December 14, 2006, 12:10 PM

Re: C2 wheel porosity......

Thanks for all the suggestions. After considering the problem, I think I'll skip mounting 5 tires and leak testing, then dismounting and leak fixing. I am fairly sure these wheels are leakers and that the easiest way around it is to seal all five before mounting tires. This may take awhile as the owner is busy with other projects, but I'll try to learn how sucessful this it and post an answer later. Thanks again! Bill

C2 wheel porosity......

C2 wheel porosity......

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