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selwyn
Joined: 12 Mar 2008
Posts: 102
Location: Australia
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 Posted: Tue Mar 08, 2011 3:26 am Post subject: Matco Brakes and Wheels |
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Hi all,
I spent most of today changing the tyres on ELZ. "That's a bit slow" I hear you say. Well yes, it is, but it turned out to be a much more educational experience than bargained for.
First off, some time in the last one or two flights one of the through bolts on the left hand wheel had broken and allowed the wheel to distort somewhat so that it did not want to slide off the axle. Easily fixed, let the pressure out of the tyre and all was well. The big question is why did the bolt break?
The fault may not be as simple as an inadequate bolt. The tubes supplied with the kit have a washer and nut on the base of the valve stem. In my example, the washer was chewed about a bit and there was some corresponding damage around the valve stem opening in the two halves of the rim. I cannot tell if this damage occurred before or after the bolt broke but it is possible that the washer became caught in the opening when the wheel was assembled, wedging the halves apart, and subsequently worked free and left he bolt loose to flex and fracture. I would like to think that I would have picked this up during assembly but the possibility exists.
I remember that others have had bolts break in these wheels so there is obviously a design fault. I wonder why Matco has not fixed it and issued some advice to operators, I also wonder why there has been no remedial advice from Arion.
I removed the nuts and washers from the valve stem and replaced all the cap screws with high tensile items which should fix the problem.
The next learning experience goes back to to a Matco service bulletin issued last year, see Lightning newsletter of July 2010 for detail. This deals with the screws which attach the brake disc to the rim and identifies problems with a screw and washer combination different from that supplied in my kit. There is also advice from Arion that the problem identified by Matco does not apply to wheels with the Allen head cap screws with lockwire safeties as in my Arion kit, and, as far as I know, most others.
I'm here to tell you that it ain't necessarily so! When I removed the cap screws securing the disc to the wheel there was evidence that the disc had been working on the screws. There was no obvious free play but the evidence of movement and fretting indicated that there was not enough tension on the fastening because the screws were bottoming out in the holes in the rim. Subsequent inspection confirmed this. The fault was not obvious in a daily inspection, even without spats fitted and I know of one other occurrence of this problem so I respectfully suggest that a careful check of your disc attach cap screws may be in order.
I shortened my cap screws by a couple of millimetres and reinstalled and I believe this will cure the problem.
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Cheers, Selwyn
Kit 66 VH-ELZ |
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info(at)flylightning.net
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| Posted: Thu Mar 10, 2011 3:50 pm Post subject: Matco Brakes and Wheels |
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The problem with the thru bolt failure is from over torque of the bolt.
The bolts are only torqued to 8ft lbs I belive, most guys tighten them
up good and don't bother to check torque here. That is the explanation
from matco, since we have started paying attention to that we have not
seen anymore bolts break.
nick
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selwyn
Joined: 12 Mar 2008
Posts: 102
Location: Australia
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| Posted: Sun Mar 13, 2011 2:12 am Post subject: Re: Matco Brakes and Wheels |
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That would not be the case here. My original installation was to the specified torque.
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Cheers, Selwyn
Kit 66 VH-ELZ |
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info(at)flylightning.net
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| Posted: Sun Mar 13, 2011 3:45 pm Post subject: Matco Brakes and Wheels |
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Not sure than, Matco advised us that over torque or under torque was the
cause. Either not enough clamping force between the wheel half's or the
bolts had been compromised from too much torque.
We have see 3 or 4 wheels do that, since advising to build the wheel per
matcos specs we have not seen it.
Nick
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selwyn
Joined: 12 Mar 2008
Posts: 102
Location: Australia
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| Posted: Mon Mar 14, 2011 12:27 am Post subject: Re: Matco Brakes and Wheels |
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OK, so where on the Arion site would I find that advice from Matco? Not that it would have made any difference in this case.
To my mind the more important point from my experience is the problems with the disc attachment setscrews. Advice provided from Matco and Arion has been shown to be inaccurate, the effect can be difficult to detect, the consequences may be serious and my advice is that owners should check their own installations.
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Cheers, Selwyn
Kit 66 VH-ELZ |
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