Fab-320 clarity

[Funguy]

I'm probably missing something obvious but here goes:

1) There appears to be only 5 AN3 bolts for 6 filter bracket positions in the supplied hardware. The online parts list also says 5 bolts. What am I missing?

2) The new arm for the carb heat door (VA-00122-1) does not show the hardware stackup for the hinge but it looks like the supplied drilled AN3 bolt, a couple of washers to capture the control wire and a metal locknut in the photos. I cannot for the life of me see how using the locknut to both capture the control wire and also set the tension on the hinge is a robust and reliable way to do this but I'm open to being shown or corrected.

3) Can I assume #12 bit to drill the carb heat door arm hinge to size?

Thanks in advance!

Cheers, Sean

 

[Cth6]

1. One of the 6 bolts is a longer AN3 for the adel clamp pinching the carb heat cable.

 

[blaplante]

I'm probably missing something obvious but here goes:
...

2) The new arm for the carb heat door (VA-00122-1) does not show the hardware stackup for the hinge but it looks like the supplied drilled AN3 bolt, a couple of washers to capture the control wire and a metal locknut in the photos. I cannot for the life of me see how using the locknut to both capture the control wire and also set the tension on the hinge is a robust and reliable way to do this but I'm open to being shown or corrected.

...

Thanks in advance!

Cheers, Sean

Photo of the diagram for us to look at?

 

[Funguy]

This is from the FAB-320 Installation instructions.

"Tighten the nut on the pivot bolt just enough to securely hold the cable but not distort it. The pivot
bolt should move freely in the Carb. Heat Door Arm bushing. Lube the joint periodically with a drop
of oil."

I figured out that the nut and washer capture the cable in shear through the hole in the bolt but does not set a tension to hold the bolt to the bushing. So the bolt can move axially about 1/32".

I'm sure it works. It just appears to place a lot of trust on "just enough".

Cheers, Sean

 

[RV7 To Go]

The arms I have had on my builds didn't have the welded on boss, just the arm with the hole. If the bolt binds when you tighten it just take some off the boss to free up the bolt so you can tighten the nut enough. I like a thick washer on both sides of the cable. The washer will put a slight bend in the cable when the nut is tightened. Never had one come loose doing that. Leave the wire about an inch too long so you can bend it over the top to prevent the cable from pulling out if it ever loosened....also less of a poking hazard that way.

 

[blaplante]

So if the cable slips, the outcome is ... ?
I certainly wouldn't accept this for throttle or mixture controls but I've seen this sort of thing work successfully for a lot of carb heat and alt air doors.

Put a control cable onto it with a heim joint end if you'd like. It's EAB, your choice.

 

[krw5927]

There are alternatives for the carb heat cable which allow the cable end to be tightened securely without affecting rotation:

Anti-Splat Aero Bowden Cable Wire End | Aircraft Spruce ®

Anti-Splat Aero Bowden Cable Wire End Anti-Splat-Aero is excited to introduce another high-quality upgradeour Stainless Steel Bowden Cable Wire End!

www.aircraftspruce.com

Cable End B Nut | Aircraft Spruce ®

Cable End B Nut This universal NAP assembly will eliminate bent or smashed push-pull cable ends and get a strong hold at the same time. The cable end lays in a machined channel at the bottom of the screw hole. ...

www.aircraftspruce.com

 

[rvbuilder2002]

There are alternatives for the carb heat cable which allow the cable end to be tightened securely without affecting rotation:

Yes there are.
And over time with the influence of vibration (this is in a very high vibration area), and the above mentioned options only baring on the relatively thin metal arm, the hole will begin to wear and become enlarged. Once the wear starts it accelerates as the hole size grows.

The arm with the welded bushing has a large amount of contact area and doesn't wear.

 

[ShawnR]

Thanks for posting @Funguy . I am at the same point in my -4 rebuild and dropped in here to look for an answer to the same question. I was wondering how we could tighten the cable to not slip and yet, still have it rotate. I get it now. Thanks to those providing the responses.