Thanks; yes, I think that might have even been suggested before. It's just a question of how to best approach the analysis: If I use the WD-40 test to look for fretting on the assembly then that would defeat the dyekem. I think that I may need to allow the assembly to settle and re-torque a...
Chamfering the edge of the crankcase seems like a good idea. I also think that your earlier idea of removing some material from the face of the crankcase dowling is good. Looking at the plate it appears there may be some contact in this area, and that would only prevent the ears from coming...
Ted, funny you should mention Bondo. I had a report from one pilot who had the top bolt location fail twice. He filled it with JB Weld and clamped it with a 12.9 grade screw and hasn't had a problem since. Unfortunately in spite of my prior claim I do find that a bit too ugly to try.
I'm a...
Ted, that's a good catch. I agree that it seems the "ears" should come together. It would seem like the machining of the counter-bore would need to be very accurate in order to ensure that the ears come together while at the same time achieving the desired clamping action by the counter-bore...
desertfox, thanks for the clarification. It does seem that your drawing is an accurate schematic representation of what is going on, I just wanted to try and head off or clear up any possible confusion over the actual configuration. This thread has evolved well beyond my original question...
For some reason only one picture seems to have made it. Here's the other.
Dave C.http://files.engineering.com/getfile.aspx?folder=15841f18-8f67-4878-95a6-9f79bcb84143&file=motor.jpg
Mike, I had to look up a Wood Screw Pump. HA! I think you are right. It's not the pressure that's going to drown me, its the sheer volume. Thanks again everyone for taking an interest in this.
desertfox, I've had a chance to look at your analysis. Thanks very much for that. If I am...
Thanks, desertfox, and thanks for joining the thread.
I'm out of town for the weekend and having a hard time with my laptop, so I won't get a chance to carefully look at your analysis until I get home to my printer. From a first glance, though It looks like you have the configuration...
Yeah, you are right, it is more of a pickle-fork.
I just pulled it apart today, and with the standard bolts and installation torque after 5 hours of running time there is noticeable fretting corrosion near the top bolt.
The good news is I have another option which I am in the process of...
Mike, I just went out to take a picture, then I remembered that I have it all torn apart to fix it! HA! Oh well, I found a picture that shows the thing folded up. If you zoom in to the propeller area you can see the motor and reduction drive. Anyhow, in normal "unfolded" mode the prop is in...
Sorry about the confusion, looks like I used the term "fretting corrosion" rather than the correct term "fretting wear". I'm trying to be careful (still trying not to call a screw a bolt). I'm just a darned electrical engineer. That's my excuse, anyway.
Mike, if I am understanding your...
Quoted from The ASM Handbook on Fatigue and Fracture (as found on Wikipedia). Fretting is:
"A special wear process that occurs at the contact area between two materials under load and subject to minute relative motion by vibration or some other force."
I don't believe there needs to be an...
I believe that the initial pre-load is insufficient to prevent relative motion due to vibration. This causes fretting corrosion which causes loss of surface material and thus further reduces the pre-load. As the pre-load drops the surfaces are more free to move putting more fatigue stress on...
Yes, I can (and will) use Loctite, although as I understand it Loctite by itself will not prevent this type of failure, since the loss of pre-load can occur without the screw ever turning.
Dave C.
Brilliant! I hadn't even considered this. Yes, I think you are understanding the geometry correctly. Tension on the belt will create flex in the plate which will be countered by tension in the top screw, thus reducing the contact pressure between the plate and crankcase in this location...
