Cowl Flap Hinge Bolt

[John J]

RHS outboard cowl flap hinge bolt continues to loosen itself on my `78 M20J (shown below).

1) How do I correct this problem? Cowl flap movement is slowly backing bolt out of integrated flap nut.

2) Is the bushing easy to replace by hand if replace bolt and washer(s)?

3) The parts catalog indicates two washers with each hinge bolt assembly (71-10-01 item #12) yet I only see one on aircraft. Where is second washer supposed to be installed?

Thanks!

[47U]

1 hour ago, John J said:

RHS outboard cowl flap hinge bolt continues to loosen itself on my `78 M20J (shown below).

1) How do I correct this problem? Cowl flap movement is slowly backing bolt out of integrated flap nut.

2) Is the bushing easy to replace by hand if replace bolt and washer(s)?

3) The parts catalog indicates two washers with each hinge bolt assembly (71-10-01 item #12) yet I only see one on aircraft. Where is second washer supposed to be installed?

 

Someone with real J-model knowledge will be along shortly…

A ‘78 J would be an early serial number, yes?  Would the applicable figure in the IPC be 71-10-00?  Index 27 and 28 relevant to the cowl flap hinge, with Note 3 reference to using -500 part numbers (depending on the serial number) and SB  M20-231.

https://mooney.com/wp-content/uploads/2020/12/SBM20-231.pdf

Regardless of everything I said above, try a longer bolt to get two or three threads protrusion through the nutplate.  

Or, do the M20-131 (if it applies).

 

[MikeOH]

I have NOT looked at the IPC, but are you sure that spacer is in the right location?  To my eye the more logical location would be between the cowl  flap and bracket with a washer on each side of the bracket (i.e. one under the bolt head and one next to the spacer and bracket).

Hopefully, a few J owners will have input/pictures to settle this.

[John J]

You are correct. I referenced IPC Figure 2 incorrectly for my serial number. IPC Figure 1 would be correct, but I don't have the setup shown with Cotter pin. From pic you can see it seems to match SB M20-231 setup as shown in Figure M20-231-5. Figure M20-231-5 does give me a better idea. I don't have the extra washer between the baffle and hinge assembly. But I'm not sure there is a bushing inside the hinge assembly at all right now which may be contributing to bolt slowly backing itself out of nut plate. What is the correct OD and length of bushing 914020-001 (so I can source one)?

Edited September 14 by John J

[EricJ]

The SB doc that @47u linked is relevant, and the last page shows a figure indicating the other washer goes between the cowl flap and the cowl.  With that additional washer it may help prevent the bolt from backing out since it'll let the bushing rotate more freely.

Early Js had some trouble with the cowl flap hinge design and the SB shows the relevant serial numbers.   Mine has been reworked a few times and needs it again, and I have to replace some of the bushings every couple of years.    Your looks very good in comparison.

On mine I make the bushings from brass hollow rod stock.   Just saw off a piece the right length.

[John J]

100% on the missing washer. Learning as a new M20J owner and didn't know about SB without asking here :-) If anyone could provide OD and length of bushing 914020-001 I'll work out the rest...Thanks!

Edited September 14 by John J

[BaldEagle]

On 9/14/2025 at 1:30 PM, John J said:

100% on the missing washer. Learning as a new M20J owner and didn't know about SB without asking here :-) If anyone could provide OD and length of bushing 914020-001 I'll work out the rest...Thanks!

Probably too late to be of any assistance, but I'm also having fun with my cowl flaps.  I pulled the cowling off to do an oil change and noticed a cowl flap bolt was missing.  Of the 3 remaining bolts two were working themselves loose and I only had one bushing, but I was able to use this as a reference for sourcing or fabricating replacements:

Length: 9.5mm

OD: 6.3mm

ID: 5mm

Or:

Length: 0.38 inch

OD: 0.25 inch

ID: 0.19 inch

These are probably not the exact dimensions as my bushing has some corrosion and wear and I used a cheap digital caliper to measure.

The parts manual show bolt AN3-7A, un-drilled bolt (I have an early J).  I decided to order part no AN3-7 so that I can install a castellated nut (AN310-3) and cotter pin (AN380-2-3).

 

[Aerospace]

I'm glad this thread exists because I am working on my cowl flaps on my '92 J as well. In my case, I need to replace these rivets:

Does anyone know what they are? AN4 solid? A, AD?

[Aerospace]

According to this SB:
https://mooney.com/wp-content/uploads/2020/12/SBM20-231.pdf
they are MS20426AD4-5 and -6

[BaldEagle]

2 hours ago, Aerospace said:

According to this SB:
https://mooney.com/wp-content/uploads/2020/12/SBM20-231.pdf
they are MS20426AD4-5 and -6

McMaster Carr is a good source, if you don’t need 1 lb bags of each…

[EricJ]

On mine I replaced them with screws and self-locking nuts.

[Aerospace]

I did consider that. A steel screw is stronger than one of those rivets.