Dan, I haven't been following the prop indexing story here too closely lately, but I hope that nobody advised indexing the prop based on where the engine happens to stop. Where the engine happens to stop is somewhat random. Yeah - it will usually stop with the prop in roughly the same place, but that's no reference to index your prop by. If you search the archives, you should find a discussion about prop indexing and vibration. This has been discussed at length before. FWIW, You may find this email of interest: Subj: Vibration Date: 2/4/99 7:57:11 AM Eastern Standard Time I had the same problem with vibration in the 1900 to 2250 rpm range on my Alon when I first got it. In one of the manuals I received with my Alon, it talked about prop orientation on the engine. Sure enough when I checked, it was not as specified in the manual. My vibration was so bad it had broken the lord mounts on the instrument cluster. The manual I have states that with the #1 cylinder on TDC, the #1 blade of the prop should be in the 10:00 postion as viewed sitting in the pilots seat. I could not find out how to determine the #1 blade on the prop so if anyone could help me with that, I would appreciate it. When I asked my A&P about it, he looked at me like I had lost all my marbles. After I got home, I made the change and could not believe the difference. Although I had the same vibration @ around 1900 to 2250, it was not nearly as bad, and I could at least do some short term slow flight. (My wife was working on MCA). I still avoid these rpm ranges as a matter of practice because of the vibration. I don't know if you have tried this or not, but it did help mine. Please accept apologies if you have already tried this. Name Removed Also: Hello from Sunny So Cal, The C90-16f has an a hormonic imbalance at 2200 rpm. You should find it in your owners manual. Do not fly at 2200 rpm for long period of time or something like that. Also I had trouble with an A&P replacing the prop in the wrong position on reinstall after dressing and repainting. With switch off and looking to the rear of your A/C your Mag should click with prop coming Thu the 8 o'clock position PLEASE be careful when checking this. By the way propellers have a #1 blade but that is another story. Best to the Commonwealth, Yours, Name Removed BTW - I think that the number 1 blade can be identified by a 1 stamped in the prop. You may have to remove the spinner or prop to see the mark though. I can't remember for sure where I found it on my prop. Also, I seem to remember that you can't really do exactly what the Alon service manual says. I'm a bit fuzzy on this, but I think the manual says the mags should click with the prop coming through 8:00, but you can't index the prop that way. You can index it at 9:00 or 7:00, but not 8:00, due to the bolt hole pattern. I think that I ended up with mine at 7:00. This is all just offered as food for thought. Don't take any of this to the bank, as it's been a while since I've messed with all this. If you want more details, let me know and I'll go look up what it says in the Alon Service Manual and see where my prop is when the mags click. But if the engine starts and cuts my arm off you owe me a beer, OK? Best Regards,
Wayne DelRossi Alon Aircoupe N5618F "Nobody has ever scientifically proven that life is supposed to be serious." **************It's Tax Time! Get tips, forms and advice on AOL Money & Finance. (http://money.aol.com/tax?NCID=aolcmp00300000002850)
