Final NTSB report N393SX Sonex

[WaiexN143NM]

Hi all,
Good reading, especially for AeroVee owners , 27 may 2017 www.kathrynsreport.com

WaiexN143NM
Michael

[radfordc]

I had a similar failure of a swivel foot adjuster once. I found the broken adjuster during a routine valve adjustment and don't know exactly how long I had flown with it broken. There was no loss of power or any other sign that the adjuster was broken. In my case the swivel pad remained in place even though the stem had broken.

[x3 skier]

The link to Kathryn's report took me to a fatal on a Free Bird with a hirth engine, 176FB ?

Cheers

[gammaxy]

Here's a better link:
http://www.kathrynsreport.com/2017/05/brandt-sonex-n393sx-accident-occurred.html

I think this quote is important:

The remaining rocker arms did not exhibit the appearance of arm adjustment in accordance with the kit manufacturer's assembly manual.

As is this:

The ball bearing on the end of the valve adjuster had seized in place and could not be rotated

This picture from the docket (https://dms.ntsb.gov/pubdms/search/hitlist.cfm?docketID=59689) shows that the other 3 adjusters don't seem to be adjusted correctly:


I feel like the report didn't acknowledge that the purpose of that cross-drilled hole is to provide lubrication to the ball bearing and that with them adjusted as pictured, there may have been little/no lubrication at the bearing. Also, the hole would have been under much more stress since it may have been unsupported outside of the rocker arm.

[WaiexN143NM]

Hi chris,
Im on my its last legs ipad, thanks for direct links. For anyone new to kathryns report, i started reading in 2011 , when i believe it became online. The post is not to criticise anyone or product, but to share the information, in the interest of safety , and all can gain knowledge from this. Thanks for the explaination of the hole in the shaft, was wondering what is was for. All aerovee people should inspect, and make sure things are adjusted properly, per manuel. Fly safe!!

WaiexN143NM
Michael
Jab 3300

[mike.smith]

This picture from the docket (https://dms.ntsb.gov/pubdms/search/hitlist.cfm?docketID=59689) shows that the other 3 adjusters don't seem to be adjusted correctly:

Wow, the nuts are barely on the threaded studs, so the studs are extended WAY too far from the rocker arms. Too many shims under the rocker shaft assembly?

[rizzz]

Too many shims under the rocker shaft assembly?

Or the push rods cut too short, it would be interesting to see the rocker arm positions relative to the valve stem mid-lift.

[mike.smith]

Too many shims under the rocker shaft assembly?

Or the push rods cut too short, it would be interesting to see the rocker arm positions relative to the valve stem mid-lift.

Short pushrods is probably a better guess.

[x3 skier]

Thanks for the new link. Burr's certainly do reduce fatigue life and that's one reason I always deburr every hole I drill, even though it's a PITA.

No info on why the gear collapsed in Kathryn's report which I guess was not investigated since the FAA/NTSB felt it was a result of the engine problem and subsequent landing.

Cheers

[jeff0196]

When assembling my AeroVee engine, I found 6 of the 8 adjusters to have burrs like this inside the oil holes. Easily cleared by hand with a small drill bit. I agree that with them out as far as they were, burr or not, they were no longer getting oil and probably not supported by threads below the oil hole.

https://www.flickr.com/photos/151238915 ... res/C2614U