After reading through several of the posts on here on installing Shoulder Harnesses on an older short-body Mooney, I figured I'd give back to the community with our process on installing inertial reel shoulder harnesses on our 1965 Mooney M20E.
Which kit we installed, and what to know before you order?
We installed the inertial reel shoulder harnesses with lift-lever buckle release from Alpha Aviation: https://alphaaviation.com/mooney-m20-a-thru-k-front-inertial-reel-shoulder-lap-belt-replacement-upgrade-lift-lever-buckle/ . Can't say enough good things about them, they were extremely helpful over the phone and when we lost some of the washers in the included minor change kit (more on that later), they were kind enough to mail me a baggie full at no additional cost.
Before you order, you need to know 3 things:
What's the attachment point of the seatbelt to the airplane? There are two. Either it is bolted on where a bolt goes through to attach it to the airplane, or it's hooked on, where there's a metal hook clamp at the end of the lap belt that hooks into the metal ring on the seat.
What colour do you want? Match the interior. We went with the Fawn, they look great!
Push Button or Lift Lever? Personal preference. They say not to use the lift lever with the manual gear, however after a half dozen flights on ours with the Johnson bar I've never had it release on me or cause issues.
Now the fun part - installing!
Set of wrenches, if I remember correctly, a 9/16ths and a 5/8ths is what we used the most
Handy phillips head screwdriver
Socket head wrench for the bolt (or you can do it with a regular wrench)
Cotter pins since you're removing the seat
Drill with multiple bits (recommended a rotary ream)
Remove the seats. You're going to need the access, and this makes it easier to unhook the old seatbelts anyways.
Pray to Al that the engineers when assembling your particular Mooney gave you a little bit of clearance between the steel bars of the cage and the skin of the aircraft. Okay, now you're ready to get started. Do the pilot's side first, it's by far the hardest, and also the one you're most frequent to use.
Remove the side-plastics on the side you're working on, for this guide, I'm going to focus on the Pilot's side as I recommend to do that one first. Remove the window surrounds - side plastics/paneling around the windows. Remove the headliner.
Now the fun part. Take the clamp, and open the clamp up by inserting a screwdriver into each hole opposite of each other so they make an X, then push against them to open the clamp up so it will fit over the tube. You're going to need to install the clamp, included with the minor change kit, around the structural tube that runs in between the two windows with the flange & screw holes facing aft. This is murder. It is very hard to get the clamp on and turned around and took us probably 3-4 hours to do it. I wish I had advice for you, but there's not really any. What we did was used the needle nose pliers to hold the aluminum around the tube back and then just brute forced it on and kept pushing/turning, pushing/turning until it was where it needed to be.
One thing that makes it a little easier - try to find the place with the most clearance between the skin of the aircraft and the tube. For us, it was at the top under the headliner. We worked it on there then just shimmied the clamp down.
Once you finally have it turned around, align the clamp to the vertical midpoint of the two windows, then use those slack-jaw pliers to tighten the clamp.
Now it's time to do a test fit. The minor change kit includes the bolt, washers, spacers, and nut that you'll need. They are going to go through the provided hole on the inertial reel box, then through the two holes on the clamp, affixing the nut on the end of the bolt (spoiler alert: tightening the bolt on to that nut is like doing open heart surgery with swiss army knife tweezers), like so.
Do a test fit with the bolt through the clamp holes. Is the clamp in the right position or is it too high/too low?
Take the plastic window surrounds you removed earlier and line it up with the bolt holes on the clamp to determine where you need to drill the hole for the bolt to go through the plastic and into the clamp. It's more of an art than a science and requires some eye-balling. Mask off the hole, then use your drill & rotary ream to drill a hole big enough for the bolt to go through in the plastic window surrounds.
Make a blood sacrifice to Al. This part took us the longest. You're going to have to put the bolt through the inertial reel box, through the plastic window surrounds, through the bolt holes of the clamp, and hold the nut at the end of the clamp in place while you tighten the bolt on. Congratulations, you've got about an inch and a quarter to work with to hold it in place, and I hope you're instrument rated because you're not going to be able to see anything as the plastic is covering it. We tried several methods to do this, including using masking tape to tape the nut to the wrench itself but no matter how tightly we got it, it never was enough to hold tension for the bolt to start to thread through. Good luck, and may the Mooney gods be with you.
Once that's on, torque it to the appropriate setting (I want to say it was 70 or 90 inch pounds) and put the plastic cover back on the inertial reel.
Reinstall the headliner, plastics, etc. into place.
Reinstall the seat, install new cotter pin, and install the lap belt back on to the seat, then do a test fit. Crack open a cold one, sit back and admire your work, and look at your watch as you realize that just took you almost a full day.
I hope you found this helpful, this was not a fun process, but I will say the passenger's side is much easier (a lot more clearance, and you can actually see!) and rest knowing your flying now just became a lot safer. Apologies for the sideways pictures, they are right side up on my computer but inserting rotated...