Breaking in bushings question

[Cooper]

Hey guys I had to replace a stinger on my cat, it got torn off somehow. I bought two just to have an extra. And just to have the slightly used one as the backup I decided to replace both with new. As I normally do I oil and chuck up a shaft in a hand drill and spin it a bit to break in the bushings. I know it's not necessary but I do. I've had some that have been tight before but both of these are very tight. I could not twist the shafts in by hand and after spinning them in the drill for several minuets, off and on because of heat generated, they are still very tight. Bushings are installed correct and to right depth. My question for you, normal? They are the lead Teflon bearings and installed in pedistal support mount stingers 3/16 drives. I'm not concerned about it as I know a few runs in the river and they will loosen up. I'm more curious of what others do for break in or if anyone goes about this as I do.

[Rocstar]

I have ran into this several times. I put the shaft in a drill and sand with a light emery cloth until I get the fit I want.

[properchopper]

I've occasionally run into this situation. I chalk it up to the inconsistent production tolerance interplay between the i.d. of the stinger/strut bore, the o.d. of the bushing and how much it compresses based on the stinger/strut bore, and finally the shaft i.d. All three components are machined in different places giving the opportunity to end up with tolerance issues once assembled. I'll sometimes, when drill-lapping doesn't loosen things up to my liking, run the shaft in front of a wire wheel brush on my bench grinder and it's worked every time. I even try to sell myself on the concept that the almost microscopic wire brush markings help to trap lubricant on a molecular level (or some such rationalization).

Partially backing up my thoughts on production-tolerance variations is a .187 cable I just used from a respected source that supplies all my cables in which the threads were cut a little deeper than I've normally found and the zuber jam nut spun right on (as did several nuts I tried). Likely the machinist was having a bad hair day or some such thing

[Chilli]

I like a little jiggle in my bushing/shaft. I usually ream it out a bit with a drill. I once ran a new strut tight hoping it would loosen up. The shaft ended up locking up and I trashed the wire drive and a ESC.

[keithbradley]

I've occasionally run into this situation. I chalk it up to the inconsistent production tolerance interplay between the i.d. of the stinger/strut bore, the o.d. of the bushing and how much it compresses based on the stinger/strut bore, and finally the shaft i.d. All three components are machined in different places giving the opportunity to end up with tolerance issues once assembled. I'll sometimes, when drill-lapping doesn't loosen things up to my liking, run the shaft in front of a wire wheel brush on my bench grinder and it's worked every time. I even try to sell myself on the concept that the almost microscopic wire brush markings help to trap lubricant on a molecular level (or some such rationalization).

Partially backing up my thoughts on production-tolerance variations is a .187 cable I just used from a respected source that supplies all my cables in which the threads were cut a little deeper than I've normally found and the zuber jam nut spun right on (as did several nuts I tried). Likely the machinist was having a bad hair day or some such thing

I've had a number of those shafts Tony. I used nylocks on them to mitigate the problem. It's definitely not just a bad hair "day" though...it's been going on for a while. Maybe he's going bald?

Chilli: Is that first sentence a euphemism?
Like Chilli, I will run a drill through the strut/stinger. The wire gauge drill bits are good for that kind of stuff. Beyond that, I will sand a flex when needed, as Joel said. It really depends on where I think the problem originated. If the struts are undersized I'll fix them. If it's just a matter of a flex shaft that's a little tight I'll sand it down.

Don't expect it to loosen when heated. Those situations typically just create an exponential heat increase until failure.

[Chilli]

The one time my mind wasn't in the gutter Keith and you had to go there...

[ozzie-crawl]

Glad this came up as i just recieved some stingers that are really tight.

[Cooper]

Well I checked the shafts and they were .193. So I ended sanding them down a bit. 3/16 is 187 so the shafts were a touch big and I would rather have to turn down the shaft vs trying to drill the bushings. Thanks again guys , I was just curious what others did and how. Now I can add to my useless knowledge base. (Just in this case it's useful) :).

[properchopper]

Spending a fair amount of time/effort competing in the Ltd. Class (with mostly AQ UL-1 motors) I've found that having a free running driveline is of utmost importance. Any extra driveline resistance can seriously stress these motors (which get stressed enough with competitive props). With higher power setups this minute extra stress may not be a big deal but it's good that all extra drag be eliminated as has been discussed here. A case in point was the string of burned up motors on my P-Ltd Cat after I went from .150 with teflon to .187 sans teflon. Going back to .150 w/teflon stopped the series of burned motors. Same thing happened with a teammate's cat. I'm just assuming (backed up by several experienced racer's agreement) that the .187 added just enough extra load to get me over the edge of damaging parasitic driveline strain.

Four more race heats tomorrow and I'm hoping that the smoke stays inside - I'm running out of spares.