PA22-150 - propeller tip tracking problem

[grtbluyonder]

I had my M74DM 0-60 prop inspected, balanced, repainted, and they did tip tracking which was OK.

Upon re-installation the tip track test showed a variance of 3/16 between the tips when the propeller was rotated. Loosening and re-tightening the bolts along with jiggling the prop did not solve the problem. It remains 3/16.

The prop is OK, the plate / ring gear assy that it mounts to seems to have slight run out (8 thousandths just inside the gear teeth), yet the tip is out of spec.

The spinner backing plate is nice and smooth. The spacers are all in the same distance.

I did notice that the generator belt "pulls" on the top of the ring gear assy skewing it until the prop bolts are tight.

Can't figure this one out - does anybody have some suggestions where the issue might be? I'm assuming that 3/16 is 3X out of spec.

Regards, Allan

[captbill1956]

Did you run a dial indicator on the crankshaft flange? Did you try re indexing the prop in relation to the ring gear assembly to see if the 3/16 stays the same or varys with the index postition. I'm sure the other guys will think up more.
Good luck on your troubleshooting.
Bill Meredith
Kingsland, TX
N7749D

[Lownslow]

OK, I don't know what you have checked or not, but a few things you haven't mentioned are very important. I am assuming that there is no know reason why the crankshaft flange would be bent from prop strike or whatever. If there is reason to believe that someone sold this AC or engine to you and you are not sure of the condition, then you need to have the starter ring gear taken off, and then have run-out checked on the flange itself. The min-max specs are in the Lycoming OH manual. I seem to recall a max of .005", but I can't verify that right now. Keep in mind a small amount of runout on the flange can equate to greater values out at the tips. One likely simpler reason you are having a problem is if the aluminum starter ring gear housing is not indexed right on the crankshaft. If you have torqued the propellor up already with it in the wrong position, then you have likely caused damage to the aluminum housing. There should be marks on the housing to match with the crankshaft when it is installed properly and the housing should be able to be pushed up flat against the CS flange without any "rocking". The later O-320's had one of the prop bushings a larger size than the others, so if they are installed wrong the dimensions and interference will cause what you are seeing. It is common for the alternator or gen belt to pull on the housing before the prop is installed. I would make sure the housing is on correctly and then check the more complicated (and more expensive) reasons for the tracking to be out of limits. Best of luck.

Lou

[grtbluyonder]

Thanks guys. I used a dial gage rubbing on the inside edge of the mounting flange just inside of the starter gear. Turning the prop resulted in a repeatable wobble with the difference between prop tips vertical of the 8 thousandths. The backside surface feels a little rough so the gage jumped around a bit as the prop was turned.

I've had the aircraft for 4 years and only took the prop in for overhaul as it was due for its 5 year corrosion check. Prop was in like new condition and the aircraft did not have a prop strike in the log books or according to people and an AME that knew the aircraft.

Unfortunately I did not do a tip check before removing the prop. If the run out on the mounting flange is supposed to be 0.005 then this is definitely a problem as it is much larger.

Looks like I need to remove the cowling and have a good look at the flange itself.

Allan