SeamusG

I need your input - looking for the cause of my bearing failure ...

I recently replaced the rusted bearing set in my Saito 82a with ceramic units from rc-bearings.com. Ifollowed Paul Macintosh's suggested procedure to install the bearings - freeze the bearings and bake the case at 350 degrees for 30 minutes, Both bearings literally fell into place with no pressure. During engine assembly I used air tool lube freely to pre-lube all of the components.

As the engine also got a new ring I ran a couple of tanks thru the engine (on our club's engine run-in table) to help burnish the ring. The engine then ran (apparently) well for 6 flights. On the 7th (this afternoon) very loud grinding noises could be heard from the ground - I landed straight away.

Observation:
. the fuel tank pressure line had come free from the muffler (unclear why it came loose)
. I think that inadvertently left a plug in the end of fuel line connected to the case breather but it was apparently blown out during flight (or Imay have forgotten to plug it in the first place)

Later, during disassembly on the bench, when I removed the crank the bearings and plastic retaining device fell out. The inner race was on the crank and the outer race remained in the case. The crank throw had started to chew into the inside surfaces of the case - a bunch of aluminum chips and slivers were found throughout the case. The cam "bay" and the inside of the case were both very well lubed (nothing was dry). The stuff under the rocker covers was very well lubed and wet as well.

I'm wondering if the prop "drive flange and tapered collet" installation might have caused the bearing to fail. When installing the prop the first time after reassembly the prop nut applies pressure to the prop which in turn applies pressure on the drive flange. The drive flange puts pressure on the tapered collet causing it to bite into the crank. (what stops the collet from being forced against the front bearing?) While the prop nut is being tightened it seems to me that it is also pulling the crank forward against the back side of the main bearing. The tighter the prop the more pressure being applied to the back side of the bearing.

Since I'm going to put new bearings in the engine and fly it again I'd hate to make the same mistake with potentially worse results.

Again, thanks for your input.

Edited ...

I just added the picture of the crank, the front bearing, the tapered collet and the drive flange.

Notice that the crank (from the right)has threads, smooth section, raised bearing seat and then the cam drive teeth. I slipped the tapered collet over the front of the crank. It seats against the shoulder created by the bearing seat. So, it makes sense that when the prop is tightened it forces the drive flange against the tapered collet which in turn wants to "seat" against the shoulder at the front of the bearing seat. However, the bearing's small race is wider than the machined section of the crank for the bearing seat so the tapered collet seats against the bearing's small race. The crank is then pulled into the backside of the small bearing's race.Seems that by tightening the prop (blah blah blah)will pull the crank snug to the backside of the small bearing's race and force the tapered collet to the frontside of the small bearing's race.

IMHO, the only way that the tightening of the prop (seating all of this junk) would affect the main rear bearing would be if the main bearing seats were not set flush in the case or the main bearing seats were too wide. Either condition would result in the crank being pulled against the small race (perhaps)forcing it out of alignment with the outer race. Subsequent side forces and vibrations encounted during "running" would cause a shearing affect between the races.

Maybe ...