M20/J Cowl Flaps do not stay closed after engine install

[JRo]

We had an engine overhaul/exchange on a '78 J model, and after the installation, the cowl flaps will not stay closed.  When we did the exchange, we converted to a -A3B6.

On the ground, the cowl flaps remain closed, but in flight, it will stay in the trail position (partially closed).  My guess is that when the shop removed the engine, they did not install them correctly.  Is there an over-center mechanism that holds the cowl flaps closed?

[KSMooniac]

Yes, there are threaded rods to adjust the lengths and you'll likely need to fiddle with those a bit... Not a big deal, just a nuisance.

Sent from my motorola edge plus 2023 using Tapatalk

[ArtVandelay]

It’s been a while, but I would check if looks like it’s installed like picture:



You can see there’s places you can adjust it.

[Beard]

Is it not said that an M20J can pick up a few knots by having the cowl flaps open just a bit.

[JRo]

21 hours ago, Beard said:

Is it not said that an M20J can pick up a few knots by having the cowl flaps open just a bit.

It's definitely more than just a bit open.  The cylinders cool quite a bit during descent.  I can hold the cowl flaps closed (with my right hand), but it's not ideal.

[PT20J]

22 hours ago, Beard said:

Is it not said that an M20J can pick up a few knots by having the cowl flaps open just a bit.

It may depend on serial number. Early Js had a flat left cowl flap and it may work on those. Later Js had a contoured left cowl flap to match right one and it doesn't work on those; the POH states that opening the cowl flaps 1/4 costs 2 KTAS and opening 1/2 costs 4 KTAS.

[ArtVandelay]

It may depend on serial number. Early Js had a flat left cowl flap and it may work on those. Later Js had a contoured left cowl flap to match right one and it doesn't work on those; the POH states that opening the cowl flaps 1/4 costs 2 KTAS and opening 1/2 costs 4 KTAS.

My 78J was retrofitted with curve cowl flap, so don’t depend on serial numbers.

[sleeper-319]

I had a similar issue on mine (an 87, but also with an A3B6 and a powerflow). In my case, the lower linkage that connects to the right side cowl flap was close enough to the exhaust that in cruise flight, it would bind up enough to prevent the cowl flaps from closing. You could sorta force it closed, but it would pop right back into trail. A very minor adjustment of the exhaust and all was fine again. You'd swear by looking at it there's no way that tiny bit of interference could have caused it, but it did.  Might not be the same issue, but it's easy to spot and fix if it is.