Matco tailwheel issue

[1avidflyer 1983]

Hi all,  I was flying the Kitfox 4 this evening and after I landed the second time and was taxiing back to take off again, something didn't feel right with the plane.  Thought it was a bump first of all, then it wallowed real good and I stopped and checked what was going on.  Here is what I found.  Bearings blew out in the Matco 8" tailwheel.  I have 150 hrs on the plane, and some of those are ski time, so maybe 125 hrs on this tailwheel.  I think all I need is new bearings and that isn't to expensive.  But here is what I'm going to do to avoid having a wheel fall off in the future.  I will install a thin washer underneath the nut, so that even if the bearing balls all fall out like they did here, the washer will keep the wheel on the axel.  Having the wheel come off at full landing speed could make for a bad day.  I had a spare wheel so it was pretty easy to get it back in flying condition, but it could have been worse.  Just figured I would give a heads up to you all.  I'm including a picture of the spare wheel where you can see how much smaller the nut is than the bearing and why the wheel was able to come off.   JImChuk

 

PS.  I had some large thin washers, 1/4" hole, and 1 1/2" diameter.  I drilled out the hole to 1/2" and put them on the Kitfox and Avid.  Wont loose a tailwheel now.  I left the small diameter washer in place as a spacer between the bearing and the large washer so the large washer wouldn't rub on the wheel.

PS   PS  I did call matco and talk to their tech guy.  He didn't think it would hurt anything as long as the washer doesn't rub on the wheel.  I was sort of suggesting that this may be something they might consider doing as well.  I know if the wheel had flown off right as I touched down, things could have got ugly pretty quick.  

 

Edited 1 Aug 2023 by 1avidflyer
fixed the problem

[nlappos 413]

Great Idea, Jim!

[wypaul 448]

Hard to imagine that those bearings went bad so quickly.  Makes me wonder if the Chinese didn’t get them packed with grease during manufacturing. I have been running the dual fork model with no issues for over 1000 hours. Fortunately with the dual the wheel cannot depart but I will pay better attention during walk around, thanks for the heads up Jim.

Good solution for a safer installation, I wonder if Matco will use the knowledge you imparted. 

[1avidflyer 1983]

 

Good solution for a safer installation, I wonder if Matco will use the knowledge you imparted. 

If bought in bulk, those washers would cost all of maybe $.25 each.  I don't see a downside for the safety added.  JImChuk

[saskavid 47]

Just at a glance I'd say/guess over torqued axle bolt and created an excessive side load on the bearings. looks like there is a grease type wetness in the wheel and the race covers.In terms of matco using any of our ideas...I know with the original matco front wheels on the avid where the inner race wants to spin on the axle because of excessive seal drag the best answer is some kind of plastic spacer between the inner races to moderately pressurize the bearing and overcome the drag. Matco's best answer is to just add unnessicary drag by tightening up the wheel nut until stops spinning on the axle and that the added drag of doing this inconsequental to the energy profile of the aircraft. They don't consider that the added nut torque with added vibration and conditions of side load will slowly over time with use lead to base metal compression of the alloy wheel with the super hard bearing cup pushing into the magnesium alloy or whatever it is.. Of course this is all just theoretical observation on my part.  

[1avidflyer 1983]

Not sure I can agree with the over torqued axle bolt theory,  The bolt is 1/2" diameter.  There is a 5/8" diameter bushing/tube that sits on the bolt and that the nut tightens up against.  The bearings sit on the tube, and are not pushed in by the nut.  The inside diameter of the bearings is 5/8".  JImChuk

[saskavid 47]

Ok then that idea is shot. didn't realize the bearings sit on a tube independent of the bolt and nut influence to side loading. In terms of bearing life I do know some of the chinese manufacture bearings that I've used to replace worn ones on my combine have demonstrated fractional service life compared to the ones they replaced. 

 

Jim: just out of curiosity how much play is there between the pipe and the bearings laterally when everything is assembled?

[1avidflyer 1983]

The bearings push up against a smaller opening in the wheel hub (shoulder) so they can only go so far in.  There is only enough room  between the bearings and original washer and tailwheel arm on the other side so the bearings and wheel spin freely.  My washer has a 1/2" hole, so it goes up tight against the end of the 5/8" tube, so the wheel still spins freely.