John J Posted September 14 Report Posted September 14 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 Posted September 14 Report Posted September 14 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 Posted September 14 Report Posted September 14 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 Posted September 14 Author Report Posted September 14 (edited) 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 Posted September 14 Report Posted September 14 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 Posted September 14 Author Report Posted September 14 (edited) 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 Posted October 10 Report Posted October 10 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). 1
Aerospace Posted October 15 Report Posted October 15 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 Posted October 15 Report Posted October 15 According to this SB: https://mooney.com/wp-content/uploads/2020/12/SBM20-231.pdf they are MS20426AD4-5 and -6
BaldEagle Posted October 16 Report Posted October 16 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… 1
EricJ Posted October 16 Report Posted October 16 On mine I replaced them with screws and self-locking nuts.
Aerospace Posted October 16 Report Posted October 16 I did consider that. A steel screw is stronger than one of those rivets.
N201MKTurbo Posted Saturday at 11:47 PM Report Posted Saturday at 11:47 PM My new OPP cowl flap hinges. I have about $180 into 4 of them. Mooney wants $485 each. Most of my cost went into the welder who welded the tubes on. 6
Igor_U Posted Monday at 04:24 PM Report Posted Monday at 04:24 PM On 11/15/2025 at 3:47 PM, N201MKTurbo said: My new OPP cowl flap hinges. I have about $180 into 4 of them. Mooney wants $485 each. Most of my cost went into the welder who welded the tubes on. What's up with 6 pilot holes for the fasteners and zero edge margin on a couple of them. That's is where you'll have a crack in the future.
N201MKTurbo Posted Monday at 04:59 PM Report Posted Monday at 04:59 PM 24 minutes ago, Igor_U said: What's up with 6 pilot holes for the fasteners and zero edge margin on a couple of them. That's is where you'll have a crack in the future. The original hinges only caught one row of rivets. The rivet line that holds the metal reinforcements on has a different pitch than the original hinges. I made the hinges the same width as the original hinges with no holes. I then matched drilled the existing holes. That is where they were. If I made them any wider at the pivot end, they would be difficult to bend because the bushing needs to clear the finger on the brake. I'm not thrilled with how they fit, but I didn't put in the the original rivets either. I doubt they will ever crack. They are made out of 0.050 4130 Chrome Moly. That stuff is very tough. The rivets set just fine and they are not very highly stressed. I could have moved the rivets , but my cowl and cowl flap stiffeners would look like swiss cheese. 1
N201MKTurbo Posted Monday at 05:09 PM Report Posted Monday at 05:09 PM This is what the original hing looked like. They didn’t have the welded on bushing. You can see they are wallowed out. The SB had only been half complied with. The cowl flaps were replaced during a gear up repair before I owned it. So the cowl flaps were updated, but not the cowl side hinges.
Recommended Posts