The bolt that attaches the right flap pushrod to the flab bellcrank has begun to interfear with the aft flap cable in the right wing. When the flaps are moved between 30 and 40 degrees the bolt snags on teh top of eh cable. There was no fraying of the cable (cotton cloth test) so no harm yet. I can move the bellcrank vertically abotu 1/8 to 3/16 of an inch. When the bellcrank is pushed to the top it does not hit the cable, but returns to the lower snagging position within 2-3 flap cycles. We looked at the left bellcrank and it too has the same verticle movement, but when it is pulled down and released, it springs back up to the raised position. Looking at the part's catalogue figure 11 I don't see any type of spring or washer inside the wing to set the spacing. I've flown the plane for about 100 hours before this showed up a few days ago.
Any thoughts, experience or suggestions? Much thanks.
Bruce
Flap Bellcrank/Cable Interfearance
Moderators: GAHorn, Karl Towle, Bruce Fenstermacher
Flap Bellcrank/Cable Interfearance
Bruce Shipp
former owners of N49CP, '53 C170B
former owners of N49CP, '53 C170B
Update...problem solved. Inspected entire flap linkage system from wing root out on both sides and found no problems. The bolt that attaches the flap pushrod was snagging the aft flap cable attached to the same bellcrank. Both bellcranks had a fair bit of vertical movement but that was deemed to be normal. The right side would snag the cable by about 1/16". The left side had only 1/16" clearance between the same cable and bolt. This was easily visible through the hole where the pushrod exits the trailing edge.
This is where it got interesting. The left side showed evidence that it had been having the same problem, even though today there was decernable daylight showing. These cables had collected a fair amount of grease in the affected area, most likely from 50 years of mechanics spraying lubricants through inspection holes. There was a noticible mark in this grease build up where the bolt was rubbing the cable on the right side. There was also a similar mark on the left, even though the bolt and cable were not hitting. The only mystery is why they would hit sometimes and not at other times.
The losution was to replace both bolts with slightly shorter ones. The parts book called for AN3-7 (this may not be the exact designation, as the parts book is at the hangar) and these left 3-4 threads showing below the top of the nylon lock nut. An AN3-6 bolt left only 1/2-1 thread showing and now provides significant more clearance on both sides. We will watch this closely over the next few months to see what changes.
Bruce
This is where it got interesting. The left side showed evidence that it had been having the same problem, even though today there was decernable daylight showing. These cables had collected a fair amount of grease in the affected area, most likely from 50 years of mechanics spraying lubricants through inspection holes. There was a noticible mark in this grease build up where the bolt was rubbing the cable on the right side. There was also a similar mark on the left, even though the bolt and cable were not hitting. The only mystery is why they would hit sometimes and not at other times.
The losution was to replace both bolts with slightly shorter ones. The parts book called for AN3-7 (this may not be the exact designation, as the parts book is at the hangar) and these left 3-4 threads showing below the top of the nylon lock nut. An AN3-6 bolt left only 1/2-1 thread showing and now provides significant more clearance on both sides. We will watch this closely over the next few months to see what changes.
Bruce
Bruce Shipp
former owners of N49CP, '53 C170B
former owners of N49CP, '53 C170B