Muffler Hitting Cowl Flap Bolt

[RoundTwo]

This has been a problem since I’ve owned the plane, and I have been unable to successfully keep the muffler separated from the bolt on the cowl flap. When the muffler is installed, it’s placed as far towards the pilot side as possible, but it seems to work its way back on longer trips. I’ve installed four new engine mounts to raise the spinner, but that didn’t do the trick either. The muffler was replaced not too long ago, and my thought is there might be an issue with how the header tubes were welded that allows it to settle in a bit too far to the copilot’s side. There is no problem with the worn area getting into the exhaust chamber at this time and all of the material removed is the outer lip that mates with the heater muff.

I’ve added a few pictures with the lower cowling on, highlighting the difference between left and right side. 
Any tips for keeping the two pieces separated would be appreciated.

[PT20J]

I have the same problem. I first noticed that the cowling was in alignment with the spinner when first installed but rocked up and back such that it was out of alignment after flight. There is a little "shelf" on the bottom of the firewall where two Camlocs attach the bottom cowling. This attach point takes up all the upward load from the air pressure in the cowling. When I pulled forward on this shelf, it had a lot of play. Cracks had formed behind where it attaches to structure. I'm currently having this fixed. When the cowling rocks up and back the bottom cowling points hit the muffler as you described.

[RoundTwo]

7 hours ago, PT20J said:

I have the same problem. I first noticed that the cowling was in alignment with the spinner when first installed but rocked up and back such that it was out of alignment after flight. There is a little "shelf" on the bottom of the firewall where two Camlocs attach the bottom cowling. This attach point takes up all the upward load from the air pressure in the cowling. When I pulled forward on this shelf, it had a lot of play. Cracks had formed behind where it attaches to structure. I'm currently having this fixed. When the cowling rocks up and back the bottom cowling points hit the muffler as you described.

I also need to get this fixed. Mine had small cracks in one corner and the shelf has worn knife edge thin.

[PT20J]

I consulted with Frank Crawford at Mooney and here is his recommendation for firewall repairs.

The firewall isn’t structural. You will need to stop drill the crack. Create a patch using .016 321 stainless steel material. Install the patch wet using CS3204-B2 sealer to seal the patch. Also rivet the patch using monel Cherry Max rivets.

[RoundTwo]

1 hour ago, PT20J said:

I consulted with Frank Crawford at Mooney and here is his recommendation for firewall repairs.

The firewall isn’t structural. You will need to stop drill the crack. Create a patch using .016 321 stainless steel material. Install the patch wet using CS3204-B2 sealer to seal the patch. Also rivet the patch using monel Cherry Max rivets.

My cracks are in the lower corners of #11 600050-50X

 

[PT20J]

Just fixed mine today.

[EricJ]

On 4/10/2024 at 7:04 PM, PT20J said:

Just fixed mine today.

Are the doublers on the bottom corners the repair?

 

[PT20J]

1 hour ago, EricJ said:

Are the doublers on the bottom corners the repair?

 

Yes. There are no rivets in the lower corners because that's where the cracks were.

It's not a great design. The hole visible on the flange on the aircraft left side (right side in the photo, and there is also one on the opposite side not visible in the photo) is where a single #8 PK screw attaches to a Tinnerman on the structure and these screws (one on each side) take up all the air load that tends to pull the lower cowling attach point forward causing the cowling to rock up and back at the top. The structure where the Tinnerman is located on the right aircraft side was also cracked (there is very little "meat" there because of a large hole to clear the nose gear pivot point bolt) and we installed a .040 aluminum doubler there with a #8 nutplate replacing the PK/Tinnerman. I may do the same eventually on the left side but it is currently undamaged.

[RoundTwo]

On 4/11/2024 at 11:56 PM, PT20J said:

Yes. There are no rivets in the lower corners because that's where the cracks were.

It's not a great design. The hole visible on the flange on the aircraft left side (right side in the photo, and there is also one on the opposite side not visible in the photo) is where a single #8 PK screw attaches to a Tinnerman on the structure and these screws (one on each side) take up all the air load that tends to pull the lower cowling attach point forward causing the cowling to rock up and back at the top. The structure where the Tinnerman is located on the right aircraft side was also cracked (there is very little "meat" there because of a large hole to clear the nose gear pivot point bolt) and we installed a .040 aluminum doubler there with a #8 nutplate replacing the PK/Tinnerman. I may do the same eventually on the left side but it is currently undamaged.

This looks great. I’ll take a look to see if I have the same interior crack. 

[PT20J]

The repair keeps the cowl flap hinges from hitting muffler. But, the cowling still rocks up and back putting it slightly out of alignment with the spinner after flight although it lines up fine when first installed. 

I contacted Paul Loewen because I heard that LASAR had some fix that no one currently there remembers. He said that Mooney used  floating receptacle Camlocs and his fix was to replace some with fixed receptacles. But, according to the IPC Mooney used floating receptacles on M20Js early on, then switched to fixed and then went back to floating. Go figure. Sure enough mine are fixed. I compared the installed receptacles and studs with new and they don’t seem worn appreciably. 

Paul’s other suggestion was to install a couple of 10-32 screws with nut plates at the bottom of the lower cowl. I’m trying to decide if it’s worth the trouble or to just leave it alone.