View Full Version : Cowl flap motors again (Please read anyway)

06-16-02, 12:52 AM
OK, it looks like I need to take the cowl flap motor journey again on my '73 P337. I will take what I learn this time and make it the first FAQ on a permanent page on the site, so we can all stop answering these questions over and over again. So, here are my current questions:

My front cowl flap motor is beginning to stick momentarily during its travel from closed to open or open to closed, i.e. it sometimes just takes a second or two to start moving, and sometimes starts moving, then stops, then finishes moving properly. This is apparent from the cockpit in that the front cowl flap takes 2 to 3 times longer to move from stop to stop than the rear does. On the ground, you can see the stickyness. There is no particular place where it sticks. My first set of questions:

1.) I doubt it is the linkage, but what should I check?
2.) Is there any appropriate lubrication for the motor assembly itself?
3.) This brand new from Cessna motor is 15 months and 158 hours old. What kind of service life are others getting from their motors?
4.) I assume this is a premature failure. Think I have any chance of getting any credit from Clyde?

Assuming I can't fix it by lubing the linkage or the motor assembly, and assuming Clyde will not replace it, I will have to do something with it, quickly, on my own nickle. More questions:

5.) Does anyone have any experience with Owen Bell's refurbished cowl flap motors? Cost effective? Recommend, not?
6.)There is another place in California (Sacramento I think) that rebuilds motors. Anybody have any experience with them? Cost effective? Recommend, not?

Although I am not interested myself, because I want this fixed before the Arlington Fly-in, and hopefully before July 4th, we may as well gather the last bit of information again:

7.) Has anyone actually installed a manual cowl flap mod? What year model aircraft? Who did the work? Recommend, not? Cost?

And lastly:

8.) Any other suggestions, sources, thoughts?



rick bell
06-16-02, 02:20 AM
the clutch on the end of the clowl moter sometimes sticks or becomes n/g. the clutch is used to stop the motor at various settings of open and not let the airstream force it closed.
my mechanic and i removed the clutch plates which allowed the motor to operate. this was over three years ago and it is still working properly and the airstream seems to have no effect on the clutch plates missing. at the time we could not locate and replacements and our fix has worked out just fine. rick

Bob Cook
06-16-02, 08:39 AM

Suggest you try cleaning the brushes and armature. You can use a form of spray cleaner.

Most likely your mechanic has cleaned the engine and has let gunk down in the motor. suggest you use a baggie to wrap it when washing down the engine compartment.

You also can have a bad connection somewhere. These motors are reliable if adjusted properly.


manual mod not recommended (personal opinion) until someone comes back with some positive information.

Lastly, check the current with an ammeter and see if the current draw is uniform over the open and close. If increased current it shows something is binding.

My front motor takes 2-3 x longer and has for past three years. Not a big concern.

Lastly make microswitch adjustments with FULL 28 volts since overrun is critical to life of motor // shouldn't be any.

Remember > Keep them clean! (applies to rest of AC as well)


06-19-02, 06:14 PM
We removed the cowl flap motor (after determining the linkage was free, etc.). It was sick on the bench as well. We disasembled it, and found it full of crap (probably from washing down the engine, possibly from spilled oil during oil change). After cleaning, the motor ran normally. We reinstalled it, and everything works great now. Both front and rear cowl flaps close and open in the same amount of time.

Along the way, I learned that Owen Bell (Aviation Enterprises, see Web Sites list on this site) has serviceable used motors for $995 exchange (no warranty) or new (approved, PMA) motors with warranty for $1195 exchange.

We put some high temp RTV around the wires going into the motor to help prevent this from happening again.

Bob, your comment about overrun and full 28V only applies to the rear cowl flap motor, correct? The only risk on the front is that it might suck the flap in a bit too far on close, and open a bit too much on open, correct? The rear actually closes against metal, and if it is adjusted incorrectly, the motor will labor too hard against the hard stop. If the rear opens too far, and the flaps are put down, the damage could be an RBT (really bad thing).


Bob Cook
06-19-02, 06:25 PM
Yes this is correct.

if the motor is still running against a load it will no doubt create problems in the long run <G>. Adjust the micro switches so the cowls just close. you can tweek it somewhat with the adjustable rod ends to insure the door is just snug.

front motor is more susceptable to gunk because of its location, not to say the rear motor cannot get dirty.


Ron Ball
06-19-02, 06:49 PM
My cowl flap on rear closes on ground, light comes on, in air, light will not come on and if leave on blows breaker. My mechanic tried to adjust to manual, but Riley modified the arm to fit air-conditioning, or some reason. He redid and now works on ground but not in the air. Suggestions?? Actually this is the least of my worries. I just time the rear and shut off switch. But need to fix, I forgot to shut off and breaker blew.

06-19-02, 07:07 PM
The glib, useless reply would be "try another mechanic".

If it is misadjusted on close, and blows the breaker, each time you do that you are reducing the life of your $1000+ motor. It is a pain to adjust, but not difficult. Just make sure you use an external 28V source to power the aircraft, and then adjust the microswitches so that the motor coasts to a stop before the cowl flap is completely closed, and that it does not open so far as to interfere with the flaps. The manual is not really a critical part of doing this, in the end...except to provide a spec for how far open the flap should be.

When you say "on the ground" it does not blow a breaker, do you mean with the engines shut down? If so, I suspect the difference is the 24 vs 28V thing that Bob mentioned. If the engines are running, the motors have more voltage to work with, and labor harder, drawing more current and blowing the breaker. With the engines shut down you have something less than 24V for power...

But that doesn't explain why the light comes on on the ground but not in flight. That confuses me...

I suspect Gmas, Bob Cook and others may have more useful and knowledgeable suggestions, but there's my 1 cent worth.