M20K/231 Alternate Air Box

[One Whiskey Hotel]

Couple of questions regarding alternate air boxes on the 231.

Mine is an aluminum box on which the forward rivets for the alternate air door hinge broke free of the aluminum, as discovered at annual. My IA is leery of the use of short bolts with locknuts, for the good reason that if one were to get loose, they’d be ingested into the turbo vanes in short order. As my alternate air door hinge is worn out in his opinion, his suggestion was to replace the entire air box with one from an ‘85 231; this air box happens to be constructed of fiberglass rather than aluminum. However, on this fiberglass box, the rivets attaching the air door hinges utilize washers on the inside of the box.

1) Is riveting to washers the way these were constructed originally? It seems to me all that would have to happen is a river pulls through one of these washers, which would be followed by the turbo immediately ingesting said washer with horrible end results. Examining the fiberglass box he had on hand, one washer is already missing....this seems like a red flag to me.

2) If one were to modify the construction of these hinge attachments with locknuts and perhaps also Loctite Red on the threads, would the risk be as great as the washer scenario outlined above? Seems to me that would never come apart again. My suggestion of this is borne from the idea that rivets appear to tear through these boxes with the constant air pressure on that alternate air door.

3) If mine (an ‘80 model) was an aluminum box and the replacement suggestion from an ‘85 model is fiberglass, does this suggests the fiberglass box is superior for some reason? Or is my aluminum air box the superior box? I suppose I could rebuild the aluminum box with the fiberglass box’s door and actuating apparatus as it does seem to work better than mine.

4) Last but certainly not least: None of these are the modified alternate air box, which should have been installed on this power plant a long time ago but wasn’t for who knows what reason. Where could one find this modification which for whatever reason never found its way onto an airplane going on 40 years of age? Lasar? Mooney? Continental?

Thank you all for your opinions.

 

 

 

 

 

 

Edited May 28, 2020 by One Whiskey Hotel