The International Cessna 170 Association

Has anybody had a door latch problem where the tiny pin disappears from the catch? Started to get out of the plane yesterday only to discover the left door wouldn't open by either handle. I think my springs are ok since the handles return to their correct positions. Used a small flathead screwdriver between the door and the frame from the outside to work the catch and get the door open. The pull bar is no longer connected to the catch. The IPC pg 60-61 calls the part (number 47) NAS-41-2-.500 "Shaft -Catch stop." I'm not having much luck finding that part yet.

Hoping there's a way to replace that little dude without removing the latch. From what I've read on here, removing the latch sounds like a bit of a pain.

Does anybody have pictures that might show what that little shaft looks like? Perhaps I could make one.

It is a small piece of steel music wire .133" or between a #29 and #30 drill bit shank by 1" long. You could use a drill shank but they will rust. You could buy a piece of stainless steel from K&S Precision Metal. 1/8 will be to small, 5/32 .020 to large but you might be able to polish it down. Tedious but I've done it. https://ksmetals.com/collections/rod?fi ... st-selling

Your mouse trap spring is not there anymore because it is held in by the pin that is missing. Maybe it's in your door. I sell replacements.

You are not likely to get it all back together without removing the latch. I know these latches pretty well and I wouldn't even attempt fixing it without removing it.

I've emailed you instructions how to remove your latch.

There are two pins at play here. The one that Bruce mentioned is the one that the catch pivots on. The other, smaller one is where the bar actuates the catch. Both were made from NAS41 piano hinge pin, 3/32 and 1/8, the idea being that you grab a chunk of hinge pin and cut the length you need. The larger pin P/N is still available at Cessna in 6 inch lengths.

Woops. Looking at your pictures closer I see you didn't loose the pin that holds the latch and pin but the pin that holds the control rod to the latch. That is .100" diameter. best I can measure it, by .5" long and it looks to be brass in my sample. I wouldn't be afraid to use soft steel here.

I'm pretty sure you will never get that pin back in through the control rod without removing the latch same as the other pin.

Paper Clip…

Another bit of advice. Before one does any disassembly of the latch at all, take about 10 pictures of it from all angles. You be glad you did.

I'm the type of guy who can disassemble and reassemble about anything but these latches have beat me more than once and I've taken a few more than most apart. Still I'm no better at remembering how they go back together.

Thanks to everyone’s help, especially Bruce with his detailed latch removal procedure, I think I’m back in business. It was tight getting that latch out and thankfully someone had done it before me so no drilling rivets. They had replaced the broken mousetraps with a single “upgraded” spring which had cause part of the latch to twist over time. By fishing inside the door with a magnet, I found the missing pin. I ground the top ever so slightly to create a burr in hopes that it won’t fall out again and reinstalled it. Then I straightened the twist out and added a second spring to the other side. Seems to be in good shape for a 70 year old mechanism.

Thanks for the assistance!

Those springs are not the Cessna "improved" springs best I can tell but springs found at Hillman hardware section. You won't be alone with locally procured parts in your latch. Amazing you found the pin in the door.

Bruce,
If the outside latch works, but the interior one just moves with no actin on the door lock, what do you think is missing that I need to replace to get the interior door handle to operate?

Thank you,
John

Not quite sure I understand.

Does the interior door handle open the latch but the handle not return to a neutral position on it's own?

Or does the interior door handle not open the latch no matter what is done with it?

If the first case, I doubt there is anything that you would want to do to fix the issue. Simply manually move the door handle to the neutral position releasing the latch to catch and hold the door open. Understand that the little mouse trap spring is the only force that moves the latch out AND rotate the door handle to the neutral positions AND in the case of external door handles with no return spring, hold that handle closed. This is a lot to ask fo that one little spring. I have no ideal how they worked right from the factory. Add 70 years of play, dirt and upholstery 3 times thicker than original pushing out on the door handle, it's no wonder the inside door handle won't return. Remove all the slop worn in the system, clean the dirt, add some dry lube and remove the thick upholstery is all I could suggest.

In the second case, which sounds like your problem, likely the long flat control "strap" is ripped and broken. There is nothing in a stock mechanism from stopping someone from turning the door handle the wrong way to open it. And when they do and continue to turn it in that direction, they will twist and rip this strap in two disconnecting it from the latch assembly. You must remove the door upholstery and with a flash light observe the condition of this strap and what happens when you actuate the door handle. I've repaired my own ripped strap and I've seen examples of other repairs to this strap but it is not an easy chore and the strap must remain thin and not have anything to catch the slots it must slide through.

Here’s the strap Bruce mentioned. The outside door handle pivots on shaft “A” and pushes on shaft “B”, which actuates the door latch. B can also be pulled by the strap by the inside handle. So either handle is able to open the door. Or should be.

The strap loops around B and is spot welded to itself. At the other end it engages with the interior handle. If that attachment fails the interior handle will move but won’t open the door.

The strap has to be carefully bent so it feeds through the door to reach the interior handle without rubbing on the door structure. And it has to be thinned/carved at the handle end, which you can see in this picture.

Edit: I see rmorton put up better pictures of how shaft B connects to the door latch, and of the spot weld in the strap.