Zenith Aircraft Builders and Flyers
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"Ultimate" Matco Wheel Leak Prevention?
When mounting tires on the split-rim Matco wheels, it seems sometimes we get lucky and the first try seals air-tight and then at other times, at least one of the wheels always has a chronic leak! Most install the wheel per Matco's directions with a generously-lubed (Vaseline or silicone paste) o-ring. Some give up and install a tube, which adds more weight and $$$.
A couple of years ago, I installed 21" Aero Classic tires on my STOL 750's 6" main wheels and used the o-rings with no problems. However, after about 18 months, the right main developed a chronic leak. I tried a shot of "Slime" tire sealant and it fixed the leak, but the tire spins up enough at take-off to produce a shuddering vibration due to imbalance as the wheel lifts-off. It's easy enough to stop it with a tap on the brake, but annoying and no one likes shuddering vibrations in an airplane!
I recently dismounted the tire, cleaned out the Slime, and generously lubed the o-ring and the groove it rests in when the wheel halves are bolted together. Using soapy water to inspect, I persistently had a leak that I could see coming from where the wheel halves are joined, bubbling up from the hole in the wheel where the hub comes through. Despite 3 attempts, it still leaked! (And yes, I did thoroughly clean the inside of the wheels and even buffed the mating surfaces with Scotchbrite in case there was a burr, etc. - I tried both 3M silicone paste grease and Vaseline for the lube.)
Finally, I tried applying a circle of a thin film of "Tite Seal" sealant, about 1/4" wide, to the inner faces of the wheels just outside the bolt circle but not on the groove where the o-ring will rest. Tite Seal has now been re-branded as "Niel Seal" but it is the exact same product. It is a thick sealant paste of a consistency similar to Pro Seal, but it is NOT an adhesive and is non-hardening and non-corrosive. (A lot of sealants are adhesive and it might make it tough to later separate the wheel halves.)
I lubed the o-ring with "EZ Turn" which is the same thing as "Fuel Lube.." Not sure of the composition, but it looks and feels like a silicone paste grease but seemed a bit thicker than the 3M product. After bolting the two wheel halves together, I also applied the EZ turn to the groove before pushing the o-ring off the rim and into the groove.
Finally, I had a good seal and no leaks! I just happened to have both of these products on-hand but they are available from Aircraft Spruce and elsewhere, Now, fingers crossed no mysterious leaks in 18 months! Ha!
John
N750A
Replies to This Discussion
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Permalink Reply by Perry Delano on
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Hi John,
Your story sounds exactly like my experience with my 701, using the same wheels and tires. No leaks on any tire for a couple years, then a persistent very slow leak on LH main (Plane has yet to do first flight). Once it goes to a certain level it does seem to stabilize, and I have speculated that pressure might be okay for flying off relatively rough grass field, but it would be nice to stop the leak. I have not tried to take wheels apart as yet, but before I do I will check out the products you mention and review your post again,
Thanks,
Perry
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Permalink Reply by John Austin on
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FAIL!!!
Well, the tire held pressure great and was no problem ... until today! :(
I went over to the hangar this a.m. to clean up the plane for the flight to Homecoming and the tire was flat! I had flown it just a couple of days ago and although I didn't check the pressure, it certainly didn't look like it had lost pressure. Anyway, I aired it up and sure enough, soapy water revealed leaking between the hub and the wheel, just as before (but not necessarily in the same relative place on the wheel).
One thing I did notice is that some of the Tite Seal had oozed out between the wheel and the hub - this completely surprised me as I thought it was too thick/viscous to do this! Anyway, I think that's why the new leak developed.
I tore down the assembly yet again, cleaned everything up, and even ran a straight edge across the inner faces of the wheel to assure there were no warps or high spots.
I'm going to reassemble and try a thin bead of RTV on the inner faces of the wheel. I didn't want to do this initially as I'm afraid the adhesive aspect might make it difficult to separate the wheel halves in the future, but at this point I don't see much alternative. I will again generously lube the o-ring with Fuel Lube or silicone grease. If this fails yet again, I think the easiest route would be to throw in the towel and insert a tube. Since I don't do extreme STOL with the tires really soft/low pressure, I think a tube will work OK if it becomes necessary!
John
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Permalink Reply by Mark Cymbaluk on
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I used clear RTV silicone....after several attempts of everything else....no more leaks.
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So far, (fingers crossed!), the thin bead of RTV seems to be holding!
John
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