Oh my Belly panel aches!

[Jpravi8tor]

Today I became a Mooney mechanic! As I lay there under the airplane removing 457 different screws to gain access to the inner workings I found myself marveling at the intricate simplicity of the design. The thought of pk screws vs machine screws kept running through my head, I have never been much of a fan of pk screws but damn they won the day! I think I would actually prefer sheet metal screws in all the belly panels!

[A64Pilot]

If they are PK screws, then you have the wrong screws which is pretty common.

You want the Tinnerman screws, the have a blunt not sharp tip, a different screw pitch and I’ve been told but can’t verify that they pull the nut plate tabs into the screw and that functions as a self locking feature

AKA type “B” trusshead screw https://www.aircraftspruce.com/catalog/hapages/trusstypeb.php

You may be ahead buying the SS screw kit for Mooney’s unless you already have a stock of screws

https://www.aircraftspruce.com/catalog/hapages/exterwasherkit.php?clickkey=23701

Edited May 15, 2022 by A64Pilot

[Guest]

14 hours ago, A64Pilot said:

If they are PK screws, then you have the wrong screws which is pretty common.

You want the Tinnerman screws, the have a blunt not sharp tip, a different screw pitch and I’ve been told but can’t verify that they pull the nut plate tabs into the screw and that functions as a self locking feature

AKA type “B” trusshead screw https://www.aircraftspruce.com/catalog/hapages/trusstypeb.php

You may be ahead buying the SS screw kit for Mooney’s unless you already have a stock of screws

https://www.aircraftspruce.com/catalog/hapages/exterwasherkit.php?clickkey=23701

Older Mooney’s have a huge variety of screws used everywhere.  PK style are quite common on the two fairings behind the cowl and the first belly panel, the second one usually has 10-32 truss head screws, then the small oval panels have countersunk 8-32 screw, then the flap cover goes back to 10-32 truss head screws.  Your J model may be similar unless it’s an 84 or newer with a composite belly fairing.
 

Clarence 

[A64Pilot]

Mines a J, his is an F. I don’t know what’s on an F, but PK screws don’t use nut plates but screw directly into the sheet metal?, and I hate them. I do my best to get rid of them, because of course eventually they get bigger.

I don’t think I have any PK screws on the belly, only ones I can think of are the close out pieces where the tail articulates, but there may be more

Edited May 15, 2022 by A64Pilot

[Guest]

The AN5308R8 (AKA PK screw) as used on Mooney airframes screw into a Tinnerman style clip nut which clips to the flanges on the belly structure.  You have to move to a much newer airframe to get away from PK style screws.

Clarence

[PT20J]

I researched this a while back when we were replacing fasteners on some airplanes at the museum.

Sheet metal screws are also called self tapping screws. Some people call them PK screws because an early manufacturer was Parker-Kalon. It's all the same screw.

But, there are different types. The two most common types are A and B. Type A has a pointed end and a coarser thread  pitch and is intended for screwing together thinner sheets of metal. Type B has a finer thread pitch and a blunt end and is intended for fastening thicker sheets of metal and tapping into castings. There is also a Type AB which has a finer pitch and a pointed end.

Tinnermans are pitched for Type B. A Type A will work in a pinch, but is a loose fit and won't hold as much torque.

The AN530 is a Type B. 

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[Jpravi8tor]

My forest had a variety of trees it certainly didn’t look like a farmer planted them!

[HRM]

15 hours ago, Jpravi8tor said:

...removing 457 different screws...

Time for a one-piece belly!