WTB: control yoke shaft p/n 710005-508 or 710072-508

[Vance Harral]

This is a cautionary tale about maintenance-induced failures.

AD 77-17-04 requires 500-hour inspections of yoke shafts.  Our 1976 M20F actually left the factory with ram's-horn yokes and large-diameter yoke shafts of the type found in M20J and later models, so one is tempted to argue the AD "shouldn't" apply.  However, the AD is technically applicable to all M20F models, and the associated SB M20-205B only permits discontinuance of the inspection if the OEM P/N 710005-508 is replaced with P/N 710072-508.  I don't know what the difference is between a 710005-508 shaft and a 710072-508 shaft, but there is no record of a replacement of the former with the latter in our logbooks.  Hence, we've dutifully pulled the yokes off every 500 hours for the inspection.

The AD was due again at this year's annual, and when we tried to remove the set screw that takes up the slack, the head broke, leaving most of the screw embedded in the yoke, with no way to turn it. 

Various techniques were tried to extract the screw: drilling, screw extractors, etc.  A half day's worth of labor by professional mechanics was expended trying to solve this problem.  Their ultimate solution was to simply wrench the yoke off the shaft, and this has scored the shaft pretty badly.

The head A&P at the shop has polished the score mark, multiple A&Ps have opined that the shaft is still airworthy with the score mark, and they're willing to sign it off as airworthy.  We're "mostly" OK with this, primarily because the shaft in question is on the co-pilot's side.  But we'd just as soon replace the shaft in the near future.  So now we're on the hunt for a replacement.  None of the salvage shops we've contacted has this item in stock.  LASAR has reached out to Mooney on our behalf, but Mooney says they'd have to fabricate a new one.  We're waiting on the quote, which I expect to be astronomical.

Really hoping @Alan Fox, @acpartswhse, or someone else here on the boards has a line on a replacement yoke shaft.  We do generally trust the shop, and believe the risk of continuing to use this yoke shaft is low.  But the no-apologies fix is to replace it.  Anyone have a source for this particular item?

[Marauder]

This is a cautionary tale about maintenance-induced failures.
AD 77-17-04 requires 500-hour inspections of yoke shafts.  Our 1976 M20F actually left the factory with ram's-horn yokes and large-diameter yoke shafts of the type found in M20J and later models, so one is tempted to argue the AD "shouldn't" apply.  However, the AD is technically applicable to all M20F models, and the associated SB M20-205B only permits discontinuance of the inspection if the OEM P/N 710005-508 is replaced with P/N 710072-508.  I don't know what the difference is between a 710005-508 shaft and a 710072-508 shaft, but there is no record of a replacement of the former with the latter in our logbooks.  Hence, we've dutifully pulled the yokes off every 500 hours for the inspection.
The AD was due again at this year's annual, and when we tried to remove the set screw that takes up the slack, the head broke, leaving most of the screw embedded in the yoke, with no way to turn it. 
Various techniques were tried to extract the screw: drilling, screw extractors, etc.  A half day's worth of labor by professional mechanics was expended trying to solve this problem.  Their ultimate solution was to simply wrench the yoke off the shaft, and this has scored the shaft pretty badly.
The head A&P at the shop has polished the score mark, multiple A&Ps have opined that the shaft is still airworthy with the score mark, and they're willing to sign it off as airworthy.  We're "mostly" OK with this, primarily because the shaft in question is on the co-pilot's side.  But we'd just as soon replace the shaft in the near future.  So now we're on the hunt for a replacement.  None of the salvage shops we've contacted has this item in stock.  LASAR has reached out to Mooney on our behalf, but Mooney says they'd have to fabricate a new one.  We're waiting on the quote, which I expect to be astronomical.
Really hoping [mention=7207]Alan Fox[/mention], [mention=12721]acpartswhse[/mention], or someone else here on the boards has a line on a replacement yoke shaft.  We do generally trust the shop, and believe the risk of continuing to use this yoke shaft is low.  But the no-apologies fix is to replace it.  Anyone have a source for this particular item?

I did the Mooney yoke upgrade in 1998 to allow me to move from the ram horns to the J style yokes. The entire kit including yokes was around $1200 back then. I think the difference between the two shaft types included a slight dimensional change requiring new phenolic shaft blocks to be used. And I think there was something also about the yoke attachment hole but can’t remember the details.




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[Marauder]

It’s interesting to see the serial number breaks don’t match the service bulletin. This is on the actual blueprints provided to me by Mooney for the yoke upgrade.





And what a blueprint it is!




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[Marauder]

And before I forget. I gave my old yokes and shafts to Isaac (the guy who built the fuel tank stripper gizmo). I know he sold his Mooney, but he may still have the shafts. They were clean.

This guy: https://mooneyspace.com/profile/11848-isaacpr7/

His N number is still listed. Maybe he gave them to the new owner when he sold the plane. Worth a look.


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[Vance Harral]

Thanks for the help, Marauder.  Unfortunately, based on an educated guess about your serial number, the yoke shafts that were in your airplane before your upgrade are likely not the same part number as the ones in our airplane.  I also note that the blueprint pics you posted don't include our serial number.

The last of the F models are a bit of a strange flock.  Mooney was in the midst of changes that would become the J, and many of the parts in our airplane appear identical to those in a 1977 J, despite having different part numbers (I suspect it's the same actual part, but renumbered).  You can see this in the applicability chart for yokes and yoke shafts.  S/N 22-1179 through 22-1245 and 22-1247 through 22-1305 have yokes like your old ones, and spec P/N 710005-506 for the right hand yoke shaft. S/N 22-1246 and 22-1306 and on have the newer rams-horn style yokes as in the J, and spec P/N 710005-508 for the right hand yoke shaft.  I don't know the difference between a 710005-506 and 710005-508 shaft any more than I know the difference between a 710005-508 shaft and the replacement 710072-508 shaft, but one presumes there is some sort of difference.  The J parts manual specs P/N 710064-502 for the early J model yoke shafts. Again, I don't know if that's really any different from the one in our airplane, or just the same part with a new P/N.  I suspect this is the sort of thing where only Mooney knows the full story.