Air Vent Stuck

[pontus]

Hello:

The air vent on my 76 M20F is stuck.  Has anyone had this problem? Are there any suggestions to try before I hire someone to tear it apart. The handle releasing the opening on top of the plane will not turn.

Gus

 

[jetdriven]

unfortunately thats controlled by a cable that looks like a cowl flap cable, ram air cable, or bicycle brake cable.

 

Is it stuck open or closed?

[pontus]

It's stuck closed. I live in Florida so I would like the air it provides.

 

Thanks Gus  

[DaV8or]

Sadly, it is most likely the cable is rusted solid from disuse and sitting outside. If your's is like mine, it's a cheap all steal cable prone to this sort of thing. Difficult to service as the rear section is riveted. If you can get it to move at all, maybe with a friend pulling up a bit on the scoop while you turn the knob, then you could try spraying penetrating oil on both ends of the cable and it may free up if you can get it to go back and forth. You and your friend will have to be careful, as all the parts in this system are light weight and a bit fragile. To do this, you'll need to take dowm the plactic panel inside and have the scoop go up a bit. If you just can't get it to budge, then I think you'll have to have an A & P drill the rivets and get at the cable. This process will mess up the paint on the rivets, visable outside. This is why many people just give up on them when they freeze up.

[pontus]

Thank you for the responses

I will try to spary lubricant. The opening does not go up much but I will try.

I may have to leave it if I must drill rivets.

 

Gus

[robert7467]

Also try it when the plane is on the ground and not moving... I tried mine in the air, and due to the wind resistance, it would not close... As soon as I did it on the ground, it closed fine...

[jwilkins]

Gus,

The cables for air vents, cabin air, and cabin heat are very prone to rusting and sticking. When I originally got my F the all these cables were stuck solid. It took a long time but I eventually got them all working freely. With patience you may be able to also.

Here's what I did:

I used spray Tri Flow and sprayed both ends of the cable, as well as the spiral metal outer jacket. On my F the spiral jacket did not have a plastic lining so the Tri Flow could eventually soak into the cable. Over a period of several weeks I would periodically soak both ends of the cable and the jacket, then wiggle the control knob as much as possible without stressing it (Judgement call here; I also gently tapped one with a small plastic hammer to get it unstuck and moving). On one of the cable that was really stuck I put the spray nozzle where the inner wire went into the outer jacker and wrapped it with aluminum foil and then electrical tape to try to force some Tri Flow further into the cable. It took several weeks and a lot of patience (which I typically am short on) but I was able to get all the cables working very easily.

If I understood your post correctly you CAN get the vent open a little bit. That is great news as it has some motion and that motion can be used to eventually spread the lube further into the cable. I like Tri Flow but other penetrating fluids might work better. Once you get it working I'd use the Tri Flow.

You really need to be patient and gentle as you don't want to break the cable and then get stuck HAVING to replace it to keep the door closed.

Jim

 

[M20F]

Quote: DaV8or

Sadly, it is most likely the cable is rusted solid from disuse and sitting outside. If your's is like mine, it's a cheap all steal cable prone to this sort of thing. Difficult to service as the rear section is riveted. If you can get it to move at all, maybe with a friend pulling up a bit on the scoop while you turn the knob, then you could try spraying penetrating oil on both ends of the cable and it may free up if you can get it to go back and forth. You and your friend will have to be careful, as all the parts in this system are light weight and a bit fragile. To do this, you'll need to take dowm the plactic panel inside and have the scoop go up a bit. If you just can't get it to budge, then I think you'll have to have an A & P drill the rivets and get at the cable. This process will mess up the paint on the rivets, visable outside. This is why many people just give up on them when they freeze up.

[DaV8or]

To keep this positive a bit, the vent, when working, does work pretty well at suppling fresh air during taxi. IMO, it is worth pursuing.

[MARZ]

Marvel Mystery Oil is the best for creep in cables - I like the smell too!!

[MARZ]

Quote: jwilkins

You really need to be patient and gentle as you don't want to break the cable and then get stuck HAVING to replace it to keep the door closed.

Jim

 

[DaV8or]

Quote: maropers

 Replacing the inner cable is possible but plan on a full day

[MARZ]

No not actually - this from my post a while ago.....

 

Finally rolled up my sleeves and attacked the vent cable - some pointers for those that want to undertake the task.

Rotary Vents - They are held to the ceiling with a stud off the knob - don't try to take it off before you remove the plate it attaches to.  There are two plates that are screwed to the roof plenum - you won't see them until you remove the duct tape.

Remove both vent plates (2) - there are 12 little screws around the edge of the plate on the right and 12 little screws and the vent door control to remove on the left.

Cable - I found a suitable cable inner from Lowes - actually a throttle cable for a lawn mower.  The cable attaches to the vent door with a clevis and to the control by slipping the coiled end over the control arm. 

The easy (relative term here) way to install the inner cable is to remove the clevis on the vent door, remove the pin from the vent door hinge and remove the door itself.  Pull the cable from the cable housing, and remove the broken end from the control end.  Cut the new cable end off straight, lube the cable and insert from the door end, feed as much as possible into the cabin.

To make the coil end on the cable - bend approximately 1/2 inch of the end to a 90 degree, you will vice grip this end to a 3/16 drill bit so the tab is aligned longitudinally to the bit.  Once secure make three tight coils around the bit, release the vice grips and cut off the 90 degree tab. 

The coiled end slips over a post on the control arm.  Once in place put the left vent assembly together temporarily and operate the control noting the movement of the cable.  Retract (close) the cable and put a mark at the point that the inner cable meets the outer housing at the vent door.   Now extend (open) the cable to give you room to make a coil on that end.  

The beginning of the door end cable coil should start approximately 1/8" beyond the mark you have made.  For this coil you will need a smaller drill bit (to match the clevis pin) and initially clamp the cable perpendicular to the bit.  I found this method to be a bit more challenging than the other but it gives the control over the required length of the cable.

Reinstall the vent door and attach the cable and test. 

Don't forget to paint the Royalite vents while they are apart!!!  Put everything back together - put bandaids on the cuts on you fingers, and your done!!

Time invested - 6 hours

Weight lost sweating in 98 degree heat 3 lbs

Parts - $8.79

Ability to control my vent door again - priceless

[KSMooniac]

PB Blaster is the best product I have found for dealing with rusty parts.  Available from any good auto parts or hardware store.  Good luck!

Nice write-up there, Mike.  

[danb35]

Another good choice is Kroil.  I get it from Brownell's (gunsmith supply shop), though no doubt there are other sources.

[M20F]

Corrosion X works great as well

[DaV8or]

Quote: danb35

Another good choice is Kroil.  I get it from Brownell's (gunsmith supply shop), though no doubt there are other sources.

[DaV8or]

Quote: maropers

No not actually - this from my post a while ago.....

[jetdriven]

Wish someone had some photos.  Our scoop only opens 1/3rd of the way.

[Vref]

pontus I feel your pain...a lot of work to get to the core of the problem...

hope this helps a bit the excellent clarifications from maropers...

Luc

[MARZ]

Front vent removed from plenum - remove front vents for access to the control cable. 

[pontus]

OK I unsrewed the plate near the handle and sprayed lubricant on the all parts inside. I will do this several times and try to move the handle. I hope it works and wish to thank you for the tips and info.

Gus

[DaV8or]

Quote: pontus

OK I unsrewed the plate near the handle and sprayed lubricant on the all parts inside. I will do this several times and try to move the handle. I hope it works and wish to thank you for the tips and info.

Gus

[pontus]

Well I must say that the tips you all gave me saved quite a bit of money. The vent works perfectly. All it took was some lubricant. I thank you all. The vent opens about one and three quarter inches. 

Thank you, Gus

[MARZ]

SWEET!!