Stripped out rear seat anchor nuts

[170 Scott]

1950 170A, 2 of the 4 anchor nuts, the forward and RH ones, that hold the rear seat in are stripped.

It looks like the seat tracks and floorboard would all have to be removed to gain access to the forward anchor nuts' rivets, and the right, rear seat bracket would have to be removed to to buck in a new anchor nut. There's no way, on the forward one, to reach through an inspection panel to put a nut onto a longer bolt either. Also, drilling and retapping it to a larger size won't work because then the seat mounting hole would have to be drilled out too.

I'm thinking of drilling out the rh one and either fishing in a new anchor nut using some string under one of the gaps in the bottom of the bracket and try and start a bolt in it to hold it while using a couple flush cherrymax rivets to remount it, or just go with a rivnut? I'm really not sure on the forward one, I really don't want to rip up the floor for this. Trim the floorboard to access the rivets or maybe drill it out and squeeze in a rivnut? Anyone had to deal with this before? Looking for your thoughts and advise. Thanks!

[c170b53]

I have the same thing with my forward floor nut plate. I've been flying with the seat removed to allow space for my camping gear and bicycle. I agree, It would be a major pain to pull the floor up just to replace it. As for the sides, I think, fishing either with fish line or a strong magnet you might position it into its new home.

[GAHorn]

An impatient installer is the usual reason for this problem. A hurried person will become frustrated with the tight fitment of this seat and force/cross-thread a fastener into the nut thereby damaging it.
Rivnut sure is tempting for the floor.

[johneeb]

Is there enough material in the damaged nut plate to put in a "Hilical' thread repair insert?

[ghostflyer]

I think the rivnut is a bad idea as I am sure they will not pass the stress test. Those 4 little bolts hold the seat and 2 big lumps of lard to the aeroplane . Use a new anchor nut but cherry max rivets could be used to hold in position .If using cherry lock rivets make sure of your grip length . Cherry max rivets are a little more forgiving in this area. Also use the outside skin panels to your benefit . I have just watched a mechanic huff and puff working on a seat rail replacement and when he was going to cut another access panel in the floor to gain access When it was pointed out there is a outside skin panel nearly under his work site .he was too focused on the floor and interior area.

[wingnut]

On the forward nutplate, the flush head rivets that attach the nutplate to the bulkhead flange are underneath the floorboards. You can use a nutplate drill jig to 'find' those 2 rivets. Drill through floorboards, removing old nutplate. Install new nutplate with button head rivets through floorboards, or use blind CCR rivets.

On the side mount, it's not but a half hour job to remove the bracket, replace nutplate with solid rivets, reinstall bracket........ but then you have paint touch up on the outside.
Remove damaged nutplate. Fish a new one up in there with safety wire or magnet. Use the Cherry 'CCR' rivets. They are 3/32" (#40) and made exclusively for blind nutplate installation.

[c170b53]

Gee thanks Del, dah...I hadn’t thought of that idea to remove the floor nutplate.

[170 Scott]

I went with Del's suggestions and they work perfectly. I actually threaded a 10-32 screwed backward onto new anchor nut and then screwed it into the one on the floor to use as a jig to drill them out. After drilling out the side one I fished a piece of safety wire through the top rivet hole and out the top of the bracket, put the anchor nut on it and it slide right in place where I could put a cleco in it.
As far as them being cross threaded, this is pretty much impossible since there's about a 1" sleeve the 3 forward bolts have to go through in the seat which keeps them aligned. The problem is the holes in the seat don't line up perfectly with the anchors, after you get 2 of the 3 forward bolts in, the third one takes a lot of force on the seat to line it up, so it has a lot of side load on it which after removing and re-installing the seat so many times will eventually damage the bolt and nuts.
Thanks for all who commented.
Scott

[wingnut]

That's using the ole bean. Yes, those back seats fit like a sock on a rooster.

[c170taildragger]

I have another question about the back seat. I took the backseat out for my first annual and realized the seat back is bolted to the bottom seat assembly. I was only familiar with the front seat in the Cessna 140 in which the bottom attachment points of the seat back are simply on a spring rod that can easily be pushed in to remove or reposition the seat back. Are there any modifications that would allow easier removal of seat back for loading baggage compartment instead of unscrewing the nuts that attach to the bottom seat assembly?

[DaveF]

My seat back is held with spring-ball pins like this. https://grainger.com/product/3HLK1

A more secure but still convenient method would be clevis pins held with lock pins. Spruce sells them.

[cessna170bdriver]

If you got the back seat out with the back still attached to the bottom without beating the crap out the rear door posts, you’re a better man than me. I replaced the bolts with spring ball pins like Dave.

[c170taildragger]

Thanks Bruce, how did you know! I did continue to look through the forum and did find the solution you folks have given.. Have to get me some of those!

[c170taildragger]

Sorry Miles . Not sure why I said Bruce probably because I was laughing so hard as I pictured my self beating the seat out of the aircraft!