Main shaft bearing question

[FlyBri3]

Is it common for the main shaft bearings to go bad and wobble with normal use? If I hold the frame still and hold the head block the main shaft has a very very small amount of movement front to back or side to side! Not up and down. I have been fighting this problem since I noticed it over a year ago. I figured it was caused by crashing and just needed to replace the bearings but I have gone through about 6 sets so far and the last 3 got replaced just because of the main shaft wobble! I just replaced the last set a few months ago and and have not crashed but they are wobbly again! Any body have this problem Or am I special? LOL

[cyclo]

No lateral movement of the main shaft on both my Atoms. Is your shaft true? If it were me I would remove it and roll it on glass to see if it is true... Or remove the head assembly and spool it up carefully looking for any wobble of the top part of the main shaft especially when it is just beginning to spool up.

[FlyBri3]

I will give it a shot, It is a new shaft and bearings tho. When I replace the bearings there is never any lateral play, then after a handful of flights the lateral play is back. so something is goofed somewhere.

[aburkhardt]

My stretched Atom eats bearings. I just replace them whenever I crash.
Btw, Boca sells a nice kit for $20.
http://www.bocabearings.com/AppByMan...&MODSYSID=9824

[Ah Clem]

"Is it common for the main shaft bearings to go bad and wobble with normal use? "

I don't believe this is common-certainly not in my experience.

My Atom 500 still has the original bearings in it-it is from 2008 and has hundreds of flights on it. I just lube the bearings with light oil or TriFlow liquid once in a while. There is no slop or play as you described.

My Stretched Atom is a bit different. I put that one in the dirt last year, so I installed a set of sealed bearings a friend gave me in that machine. Should be interesting to see how these last over time-unlike the stock shielded bearings, you can't lube them, but they should pretty much seal out any dirt. They have a little more drag, but it does not seem to affect performance any.

[FlyBri3]

Hum, not sure where to go with this one now! LOL As goofy as it sounds could the bearing blocks somehow get distorted and cause the bearings to wear faster? The lateral play isn't really isn't even visible when you wiggle the head but you can definitely feel it!

[Ah Clem]

Is the play in the bearings themselves, or the fit of the shaft in the inner race of the bearings?

[aburkhardt]

I must clarify "my stretched atom eats bearing" statement: after 100 or so flights bearings are "notchy" not sloppy.

[TheBum]

A crash can damage bearings, causing flat spots on some of the balls and, therefore, notchiness. I always check them after a crash and have to replace them about 20% of the time.

[FlyBri3]

Originally Posted by Ah Clem

Is the play in the bearings themselves, or the fit of the shaft in the inner race of the bearings?

It's hard to tell which is the culprit. I guess I just assume its the bearings because when I replace them the slop seems to go away until about 20 flights or so then shows up again! I can't imagine the main shaft wearing at the bearings causing the play? One thing I have been learning in this hobby tho is the fact that it doesn't always make sense as to why something goes bad! LOL

[fjoe]

Does your main shaft drop down through the bearing blocks freely? Any chance your main bearing blocks are not lined up properly?

[cyclo]

Originally Posted by fjoe

Does your main shaft drop down through the bearing blocks freely? Any chance your main bearing blocks are not lined up properly?

+1 on this suggestion. With only two bearing blocks on the Atom the shaft should go through the blocks smoothly.

[FlyBri3]

Originally Posted by fjoe

Does your main shaft drop down through the bearing blocks freely? Any chance your main bearing blocks are not lined up properly?

I am thinking the shaft goes in smoothly, but I will definitely check that out when I get a chance. I had not thought of that but I could see that causing havoc on the bearings.

[FlyBri3]

Okay guys apologies for taking so long to reply! Been busy with work and building my TSA 700e! I finally had some time and decided to do a complete tear down of my Atom and while doing so have found a few things.

First I pulled the head and main gear off to check if the main shaft dropped in freely. Yes it does without any binding what so ever. Out of curiosity I did put a small framing square on the bearing blocks to check for alignment, well they are out by about .5-1 mm from each other! So possibly causing my bad bearing issues?

The bearing blocks themselves are not bent that I can see. I have stacked them on each other to check for any bends also laid them on the floor and on a small mirror and they are very flat! There is a small bit of play in the mounting hols on the CF frames for the lower bearing block, so maybe just enough to knock them out of alignment? Not sure.

Also I have some cracks in the CF frames and some warping in various places.

Not really sure where to go from here? I know sometimes changing one or two parts at a time is the only way to really track down the issue. But with this poor little bird being out dated Should I just retire her and move on or just buy a bunch of new parts and hope she will be good as new?

What do you guys think?

[chalmene]

I have had shaft bearings do this on some helis in the past, none of my compass though to be clear. Could be a lot of factors really, that are causing your bearings to wear out prematurely. If the cracks in your frame are causing flex near your head bearing blocks, could be a possible cause.You could always try different types and see if you get the same result. Personally, if everything is straight and true, and the play isn't serious and isn't affecting performance at all, I wouldn't even worry about it. An old bird I have has more play than what you describe and it doesn't affect things in the least.

[FlyBri3]

I have been putting my Atom back together slowly. When It came time for the bearing blocks I screwed them in and dropped the main shaft through. It went ok, but wasn't spinning as freely as I thought it should be. I loosened the lower bearing block dropped the shaft back through and tightened it back up. Now the shaft seems to spin more freely in the bearings than before! So maybe it was just a case of misalignment?

[Rob43]

Yes, suspect so. When you tightened them before the shaft was in, they had only the tight clearances in the frame holes to position them. The shaft is more precise for the alignment task.