67 M20F Overhead vent cable

[TNIndy]

I've found a few old threads on this but when I try to open the pictures nothing comes up. Can anyone tell me how to replace the over head vent cable in a 67 M20F? I've taken the access panel off the front, removed the knob, nut and bolt so that the geared mechanism is loose. The cable shielding is secured so that I can't pull it out enough to disconnect the cable or shielding. 

[gmonnig]

Underneath all that goo, is #6 or #4 screws. You have to remove all of those. The cable is held on the aft area with a clamp just before it connects to the top door. The knob comes off from the set screw, then a nut hold the mechanism on the sheet metal. If the cable is broke, obviously you’ll need a new one. Mine was not broke. It actually had a sheared spring pin that was connected to the arm that moved the door up and down. I don’t think this was any easier than a broken cable. I had to take aluminum stock and make a new arm, drill it out, and install a new pin. While everything was out, I cleaned up corrosion, painted everything, lubed everything, new hardware and sealed everything up with real duct tape. Worked out beautifully. Also installed a new speaker while the headliner was out!

[TNIndy]

Thanks! Your rear air box is a little different but not enough to matter. I cut the goo with a razor knife but seems I will need to drill the screws out. I removed my speaker. It was shot and I don't think it's needed/required. 

[Mcstealth]

1 hour ago, TNIndy said:

Thanks! Your rear air box is a little different but not enough to matter. I cut the goo with a razor knife but seems I will need to drill the screws out. I removed my speaker. It was shot and I don't think it's needed/required. 

Hmmm. If it is on the required equipment list, I would hesitate removing it just for the lawyer reasons. 

Thinking out loud, that is all. 

[gmonnig]

Yeah, plus the replacement speaker is just $50 from Spruce. It's an easy fix. My speaker was working ok and I still decided to change it. I really don't wanna take the headliner down for the next 5yrs so it's easy insurance 

[TNIndy]

My understanding is that if it's not listed in the Type Certificate, it's not required. 

[KSMooniac]

Be careful "cutting" sealant with a razor and scoring your aluminum roof!  I know the roof skin isn't structural per se, but you don't want to create a crack-starter or corrosion initiating point.  Sealant is best removed with non-marring scrapers, and heat helps as well.  The Yard Store (Wichita, KS) sells all manner of sealant scrapers, including some nifty rotary bits for a drill or die grinder.  I used a variety of tools on my cabin skin last year doing an overhead vent conversion...which included removing that pop-up scoop and plenum, and a lot of sealant.

I have most of my leftovers from that conversion, to include scoop, cable, knob, plenum, etc. except the interior plastic vent louvers in case anyone needs parts.

[Mcstealth]

1 hour ago, TNIndy said:

My understanding is that if it's not listed in the Type Certificate, it's not required. 

That's why I used the word "if". I have no idea one way or the other.

[TNIndy]

13 minutes ago, KSMooniac said:

Be careful "cutting" sealant with a razor and scoring your aluminum roof!  I know the roof skin isn't structural per se, but you don't want to create a crack-starter or corrosion initiating point.  Sealant is best removed with non-marring scrapers, and heat helps as well.  The Yard Store (Wichita, KS) sells all manner of sealant scrapers, including some nifty rotary bits for a drill or die grinder.  I used a variety of tools on my cabin skin last year doing an overhead vent conversion...which included removing that pop-up scoop and plenum, and a lot of sealant.

I have most of my leftovers from that conversion, to include scoop, cable, knob, plenum, etc. except the interior plastic vent louvers in case anyone needs parts.

Do you have any pics after your conversion? 

[KSMooniac]

27 minutes ago, TNIndy said:

Do you have any pics after your conversion? 

Not handy, and I don't think I bothered to take any before fitting the headliner!  My bad... I was in a hurry trying to finish it last summer.  Basically I transplanted the entire system from an '81 J into my '77 J, to include dorsal fairing with intake NACA duct, plumbing pipe, valve, overhead plenum + hoses, headliner with eyeball vents, etc.  @jetdriven has also done this work on their '77, as did @testwest on his former '77, so I'm not the first to do this.  It is a very worthwhile project, but labor-intensive.

[EricJ]

2 hours ago, gmonnig said:

Yeah, plus the replacement speaker is just $50 from Spruce. It's an easy fix. My speaker was working ok and I still decided to change it. I really don't wanna take the headliner down for the next 5yrs so it's easy insurance 

There's nothing special about the speakers AS sells other than the price.   Speakers like the Realistic model listed in my IPC are no longer made, so a close match that is safe for operation is practical. 

This was the closest thing I could find.    Works great, the mounting ears are even the right spread.   I'm sure there are others that would work as well.

https://www.amazon.com/gp/product/B01N4NY1KE
 

[Yetti]

Just replace the inner core with proper sized Bowden Cable.  Or piano wire.

[TNIndy]

On 6/20/2023 at 7:43 PM, Yetti said:

Just replace the inner core with proper sized Bowden Cable.  Or piano wire.

That's was the original plan. I couldn't get the front end pulled forward enough to take it loose. I pulled it out today after removing the rear clamp and hope to reinstall tomorrow with Teflon coated stainless spring wire.