Cabin Vents Leaking air

[Niko182]

For a while now I've started doing some longer flights at higher altitudes and leaking vents haven't been an issue, since in the summer around the SW, even in the mid teens it's pretty warm. However now in this season with the OAT getting way below freezing, It has now become an issue. The cabin air vent leaks a bit of air, however the 2 side vents leak a considerable amount of air and that happens to be where the main issue lies. I removed the 2 side vents and compared it to the parts illustrated catalog and both vents seem to be different than shown in the PIC. I have pictures and it seems relatively easy to fix, but I figured I'd ask here in case anyone has some tips. This is what It looks like compared the the parts illustrated catalog. I don't seem to have the cup(33) on either side.

Thanks for any help in advanced,
Nik

[PT20J]

Sometimes the wemacs get gummed up and don’t close completely. You can take them apart from the rear and clean and lube them. 

The wemac flange should be sealed where it attaches. The trim ring is upside down in the picture, but I assume it was originally installed correctly so that the countersunk holes fit the screws. 

[Niko182]

On 12/25/2021 at 5:57 PM, PT20J said:

Sometimes the wemacs get gummed up and don’t close completely. You can take them apart from the rear and clean and lube them. 

The wemac flange should be sealed where it attaches. The trim ring is upside down in the picture, but I assume it was originally installed correctly so that the countersunk holes fit the screws. 

I'm a bit confused as what you mean the trim ring is upside down. as far as the leak goes, the cabin vents don't leak. The area that leaks is the gap between the 2 panels. The air goes through the inlet scoop on the exterior of the aircraft and goes in between the 2 panels. I'm trying to figure out how it is supposed to be sealed off, because I don't think it is supposed to be this way. I drew a picture to try to explain. I might as well tag other LB owners as they might have an idea or a fix or those that consistently work on them. @StevenL757 @GeeBee @M20Doc@carusoam

[PT20J]

I'm not clear about the picture of the wemac. Now that I enlarged it and looked at it again, it looks like it is just the wemac and perhaps the holes have been countersunk and the trim ring is not pictured.

The way my '94 J works is the wemac valve flange seals against the skin with duct sealant and protrudes through the hole in the sidewall panel. Then the metal trim ring goes on over the sidewall panel and the four screws go through the trim ring, the sidewall panel, the wemac flange and into tinnermans in the skin.

Skip

 

[Niko182]

2 hours ago, PT20J said:

I'm not clear about the picture of the wemac. Now that I enlarged it and looked at it again, it looks like it is just the wemac and perhaps the holes have been countersunk and the trim ring is not pictured.

The way my '94 J works is the wemac valve flange seals against the skin with duct sealant and protrudes through the hole in the sidewall panel. Then the metal trim ring goes on over the sidewall panel and the four screws go through the trim ring, the sidewall panel, the wemac flange and into tinnermans in the skin.

Skip

 

Would you mind taking a picture next time youre at your plane?

[PT20J]

9 hours ago, Niko182 said:

Would you mind taking a picture next time youre at your plane?

I will try to remember, but a picture wouldn't show much when it's all assembled. I made a sketch showing how mine goes together (pardon my drawing skills ) For the sealant, I used regular duct seal because it is easy to remove if necessary https://smile.amazon.com/Ideal-Industries-31-601-Duct-Block/dp/B003MZK122/ref=sr_1_4?crid=Q6Z62E8X5QAF&keywords=duct+seal&qid=1640630281&sprefix=duct+seal%2Caps%2C159&sr=8-4. 

If this is the way yours goes together, it requires removing the interior trim and positioning the wemac over the opening in the scoop skin (the sealant will hold it in place) and then placing the trim over the wemac.

Skip

[M20F-1968]

When I did my rebuild I installed the interior so that the Wemac aluminum flange is sealed against and screwed the structure of the dict leading to the outside world.  That way water can not come in and soak the carpet and interior panels that are in between the duct and the Wemac flange.  The panels then have a cut-out and the interior panels are just held against the sealed Wemac.  At one point I made a decorative ring out of aluminum but never installed them.

John Breda

[Yetti]

so if the interior panel is not drilled bigger than the screw, the screw will pull it away and leave a gap between panels.   You could drill the interior panel.  Or use some aluminum tape to seal the gap between the panels and provide some clamping so the screw does not pull the panels apart.

[Guest]

Skip’s drawing above makes the most sense, although many are not assembled this way.  On many airframes the the Tinnerman nuts are missing, so the screws won’t draw the layers together sealing the cold air out, even when the vent is closed air leaks from between the scoop and the side panel or Wemac vent.

Clarence

[Niko182]

12 minutes ago, M20Doc said:

Skip’s drawing above makes the most sense, although many are not assembled this way.  On many airframes the the Tinnerman nuts are missing, so the screws won’t draw the layers together sealing the cold air out, even when the vent is closed air leaks from between the scoop and the side panel or Wemac vent.

Clarence

The part that confuses me is that the screws that were on the airframe arent long enough to reach the tinnermans and are too large in diameter to fit them.

[PT20J]

33 minutes ago, Niko182 said:

The part that confuses me is that the screws that were on the airframe arent long enough to reach the tinnermans and are too large in diameter to fit them.

I have run into a number of issues over the years where someone before me had taken things apart and not put them back together correctly. Sometimes the IPC has enough detail to figure it out and sometimes not and you have to look at another airplane or just noodle it out. (I once spent hours rebuilding an elevator trim position sensor on the museum Beech 18 that someone before me had jury-rigged. With no drawings it was trial and error until I finally figured it out.) Point is: never assume that the way you found it is correct .

Skip

[Niko182]

well as one problem gets solved another one gets created. I went ahead and bought some different screws and some duct seal and that did the trick very nicely. however, now the there is a nice seal around the side cabin vents, the pressure increased around that area and the lower cabin vent is now leaking more air. I already checked the tension of the cable  for the main vent to make sure its sealing well and it was. any ideas how to get it to seal a bit better?

[PT20J]

I would start by removing ducts so I could visually inspect the valve to see where it is leaking. 

[carusoam]

On 12/27/2021 at 10:16 PM, Niko182 said:

well as one problem gets solved another one gets created. I went ahead and bought some different screws and some duct seal and that did the trick very nicely. however, now the there is a nice seal around the side cabin vents, the pressure increased around that area and the lower cabin vent is now leaking more air. I already checked the tension of the cable  for the main vent to make sure its sealing well and it was. any ideas how to get it to seal a bit better?

With long bodies…

There are two versions of the cold air butterfly valve up front…

Find out if your butterfly valve has holes in it intentionally…

I believe Mooney added the holes as a safety mechanism…

It constantly bleeds cold air into the system… so if you open only hot air… it doesn’t air-fry your charts on the floor…

 

It could also indicate that your rubber seals around the butterfly valve have aged… and not working as seals any longer…

PP thoughts only,

-a-

[Niko182]

Just now, carusoam said:

I believe Mooney added the holes as a safety mechanism

Mine has 2 holes in it

[carusoam]

Niko,

How do you feel about adding enough hot air to not notice the added air flow coming through…?

 

You can always block the holes in the butterfly valve for testing the seal…. Reverse Vacuum cleaner airflow studies….

I just add warm air until it isn’t noticeable…

My wemacs seam to be pretty well sealed still…

So much better than my old M20C, where everything leaked including the door seal….  

Best regards,

-a-