Engine Click... solved
Posted: Wed Jul 02, 2014 11:39 pmI thought I'd pass along a little information on something that I just solved on my AeroVee. I only have less than 4 hours on the engine. I was religious about following the assembly instructions, and using Loctite.
After my last flight, when I rotated the prop I got a loud metallic clicking from the area of the flywheel in the rear. No idea what it was, but I certainly wasn't going to fly until I fixed it. I thought it might be related to the recent service bulletin about the 4 short cap screws. I did the service bulletin for the new screws, but that was not the source of the clicking. My screws were indeed the shorter ones, but they were firmly seated and set with Loctite.
The clicking was caused by TWO things: movement of the stator ring, and movement of the alternator mount plate (that the stator ring is attached to).
Stator Ring: this ring is attached with 4 screws during assembly. I only found the ring was loose by grabbing the mount plate and the ring, and twisting. The ring moved. Not a lot, but it moved. I never would have found it if I hadn't decided to do that twist. When I started backing out the screws, they were easy to back out. Not overtly loose, but easy to start moving with a hex wrench. When I got the screws out, they had a lot of black gunk on the screw threads (no idea what it was), and a definite blob of Loctite near the end of all the screws. I had to work to get the old Loctite off. I cleaned the screw threads and secured them again with Loctite, but this time I used the Loctite primer that I got to secure the screws in the service bulletin.
Alternator Mount Plate: I put the stator assembly back in place and put 2 screws loosely in place, figuring that would hold the plate while I turned the prop. The click was still there. It was much less, but still there. Rats. But in moving the prop back and forth and listening for the click, I finally realized it was the alternator mount plate that was moving ever so slightly. There is some play between the side of the screw holes, and the screws. The powerful magnets attract the points around the stator ring, building up kinetic energy as the prop/magnets are rotated. Once the prop was rotated a few degrees the stator ring finally pulled away from the magnetic field and then banged against the side of the screws, making the click. I tried tightening down 2 screws temporarily, very tight. No more click! So I cleaned the 6 screws and installed them with the primer and Loctite, and tightened them down. No clicks and all seems well!
Now this is all a little weird. The stator screws had Loctite on them, but they obviously loosened during the 3+ hours of engine run time. I'm hoping the use of the primer will solve that issue. The alternator mount plate has SIX screws! How all 6 could be loose enough to allow the plate to move is beyond me. But again I hope the primer and Loctite will solve that as well.
If you already have your engine installed, you might consider checking these things at your annual condition inspection. If you are building your engine, really make sure these are tight, and go ahead and use the primer. It can't hurt.
===============
As an aside, to do the service bulletin you have to remove the starter. Many of you know my flywheel magnet faux pas, where I had to remove the engine from the back plate to flip the magnet. Guess what. With the starter removed, the magnet is fully accessible right there where the starter sits!!! I didn't need to remove the engine!
Many lessons learned.
Mike Smith
N439M
After my last flight, when I rotated the prop I got a loud metallic clicking from the area of the flywheel in the rear. No idea what it was, but I certainly wasn't going to fly until I fixed it. I thought it might be related to the recent service bulletin about the 4 short cap screws. I did the service bulletin for the new screws, but that was not the source of the clicking. My screws were indeed the shorter ones, but they were firmly seated and set with Loctite.
The clicking was caused by TWO things: movement of the stator ring, and movement of the alternator mount plate (that the stator ring is attached to).
Stator Ring: this ring is attached with 4 screws during assembly. I only found the ring was loose by grabbing the mount plate and the ring, and twisting. The ring moved. Not a lot, but it moved. I never would have found it if I hadn't decided to do that twist. When I started backing out the screws, they were easy to back out. Not overtly loose, but easy to start moving with a hex wrench. When I got the screws out, they had a lot of black gunk on the screw threads (no idea what it was), and a definite blob of Loctite near the end of all the screws. I had to work to get the old Loctite off. I cleaned the screw threads and secured them again with Loctite, but this time I used the Loctite primer that I got to secure the screws in the service bulletin.
Alternator Mount Plate: I put the stator assembly back in place and put 2 screws loosely in place, figuring that would hold the plate while I turned the prop. The click was still there. It was much less, but still there. Rats. But in moving the prop back and forth and listening for the click, I finally realized it was the alternator mount plate that was moving ever so slightly. There is some play between the side of the screw holes, and the screws. The powerful magnets attract the points around the stator ring, building up kinetic energy as the prop/magnets are rotated. Once the prop was rotated a few degrees the stator ring finally pulled away from the magnetic field and then banged against the side of the screws, making the click. I tried tightening down 2 screws temporarily, very tight. No more click! So I cleaned the 6 screws and installed them with the primer and Loctite, and tightened them down. No clicks and all seems well!
Now this is all a little weird. The stator screws had Loctite on them, but they obviously loosened during the 3+ hours of engine run time. I'm hoping the use of the primer will solve that issue. The alternator mount plate has SIX screws! How all 6 could be loose enough to allow the plate to move is beyond me. But again I hope the primer and Loctite will solve that as well.
If you already have your engine installed, you might consider checking these things at your annual condition inspection. If you are building your engine, really make sure these are tight, and go ahead and use the primer. It can't hurt.
===============
As an aside, to do the service bulletin you have to remove the starter. Many of you know my flywheel magnet faux pas, where I had to remove the engine from the back plate to flip the magnet. Guess what. With the starter removed, the magnet is fully accessible right there where the starter sits!!! I didn't need to remove the engine!
Many lessons learned.
Mike Smith
N439M