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Saito2

Bearing slop

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Is it normal to have some degree of slop in bearings? I've noticed this in several cases. The pinion in the rear axle assembly of my re-re Bruiser walks all around which I imagine isn't good for the ring and pinion mesh in the axle. Part of it is the sloppy diecast axle halves but some of the movement is from the bearings themselves. My Axial SMT10 front stub axles move about in their bearings too. In this case the bearings fit nice and firmly in the knuckles, so all the slop I'm seeing is between the outer and inner races of the bearings themselves. Is this normal or do higher quality bearings not have this issue?

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40 minutes ago, Saito2 said:

Is it normal to have some degree of slop in bearings? I've noticed this in several cases. The pinion in the rear axle assembly of my re-re Bruiser walks all around which I imagine isn't good for the ring and pinion mesh in the axle. Part of it is the sloppy diecast axle halves but some of the movement is from the bearings themselves. My Axial SMT10 front stub axles move about in their bearings too. In this case the bearings fit nice and firmly in the knuckles, so all the slop I'm seeing is between the outer and inner races of the bearings themselves. Is this normal or do higher quality bearings not have this issue?

In my experience some bearings are better than others in regards to slop.

I usually use cheapo Chinese ones but try and at least select ones with a decent *claimed* abec rating and they seem to be pretty good on the whole.

Some of the worst ones I've ever encountered were on a Chinese RTR buggy, very sloppy. Worse still was a pack of two Traxxas ones, one of them I literally dismantled with my fingers.

Anyway, long story short, yes the quality and tolerances vary a lot. Unfortunately it seems price/brand alone isn't a guarantee of quality.

You can at the very least remove play between the bearings and bearing carrier when it occurs. Something as simple as clear nail polish can be enough to close the gap.

It can be hard to pin down a truly reliable source of high quality bearings, many of the more famous RC bearing sellers dont even give abec ratings and even then, abec ratings are so open to "interpretation" by the manufacturer that it's by no means a reliable yardstick either.

There are one or two RC bearing sellers that are much more stringent about quality and there's always the option of buying a known bearing manufacturer brand rather than an RC brand. Brands such as NMB, SKF etc tend to be very true to their specs and claims albeit at a cost for small quantities.

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I've definitely noticed this too, and as mentioned above, price is not a guarantee of quality. It has been a while since I saw a bearing so sloppy it was useless, but they definitely vary. I have been buying bearings almost exclusively from Fast Eddy or TRB on eBay. TRB claims ABEC grade 1, which is better than nothing, and most of them seem OK. Fast Eddy doesn't mention a grade, but they feel about the same. A little play here and there, but not terrible.

One thing I have noticed is that I'm more likely to see a sealed bearing with slop in it than a metal-shielded one. I suspect that some manufscturers disguise looser bearings by adding the rubber seal to make them look tighter, whereas the metal shield can't hide the slop. The last batch of 1/4 x 3/8 pan car axle bearings I got from Fast Eddy were shielded, and they were dead-on. Rubber sealed 1150s purchased at the same time were hit-or-miss, but all still useable.

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Technically, there shouldn't be noticeable slop. That is why I finger roll them before I install them. 

Some of them have too much slop, it might run okay with a lot of grease. (At the expense of rolling efficiency, of course.)  Too tight a bearing might loosen up as it wears down (if you run them without any lubrication for even 5-10 minutes).  

ABEC rating feels counterintuitive to me.  ABEC 1 isn't the best, it's the worst of the 'Precision Bearings.'  At 0.001-0.002mm deviation allowed, ABEC 9 is the best tolerance.  But having 0.001mm deviation allowed doesn't mean that they designed a 0.001mm gap.  They could design the gap between ball bearings and the races to have a gap 5 times larger than the tolerance.  

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If the bearing company wants the least rolling resistance without much load, they'll make it looser.  If the bearing company expects a lot of load, they might make it tighter.   

RC cars being light (compared to skateboards, cars or trains), somewhat loose bearings are better. (The only exception to this is motor bearings, because of the speed, motor axle bearings tend to be very tight.)  Even for that, I bought the cheapest Chinese bearings (no ABEC ratings).  Oddly those motor bearings are very tight. 

Generally the problem is two folds.  1) Since most Ebay sellers would slap on ABEC on most bearings, you can't tell which is true and which is not.  2) Inconsistency.  Cheap bearings might be rejects. But that doesn't mean that some were intended to be ABEC2, but didn't meet the quality control and sold cheaply.  I only use 7-8 bearings out of 10.  But at about $3 per 10, I don't mind testing them.  Better bearings cost about $10-$15 per 10.  For stuff like Konghead, they cost about $40-$45. XbxyeGc.jpg

I'd rather spend $18 for 60 and use only 50 of them after a 10 minute finger-rolling test. For the money saved, I could buy 2 Sport Tuned motors. 

[Above is my toilette paper test (not paper towel, but TP). While holding the inner race, I try to roll the outer race with a folded edge of TP. If it rolls easily, it's good. If it doesn't, it's too tight. This is the cheapest bearings; about $3 for ten. I did replace heavy grease with very light grease. All my gears get these. But for wheel bearings, I leave heavy grease in tact. They fail my TP test, but they need heavy grease because of the weight on them.]  

If you don't want to bother, RCMart sells Yeah racing bearings.  They are not expensive. They should be good quality bearings. https://www.rcmart.com/yeah-racing-rc-ptfe-bearing-5x11x4mm-10pcs-yb6014b-s10-00001611

Even with cheaper ones, I very rarely come across sloppy bearings that I could feel.  After washing out all the grease, many of these cheap bearings would spin flawlessly like a fidget spinner.  Some would have some minute slop when it's totally free of lubricant. But even a drop of light machine oil would make it very hard to feel the slop.  So if you could feel the slop on RC 1150 bearings, I'm afraid that's not a good news.  

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Yeah a few bearings I have got at various stages  outside the usual ones I’d buy have been terrible for play/slop. I normally shim out a car so disappointing when you get find a few bearings like that after building. As above most have been ok/ workable.

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I'm not sure what brand bearing are in the SMT10 but the Bruiser is using the Tamiya kit bearings. I generally can't feel the slop with the bearing on the bench. It usually shows up when a shaft is put through it and wiggled (additional leverage makes it easier to see. The slop probably isn't and issue if the length of the shaft is supported on both ends by bearings, but shorten that shaft length up (like a front stub axle) and throw a big ol' tire on one end and things get all wobbly. The Bruiser's axle pinion bearings are probably the most detrimental. By design, only one end can be supported and the sloppiness effects gear mesh directly. Perhaps I will try some of the TRB bearings @markbt73 mentioned.

 

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The other thing to bear in mind is the quality of the housing you're putting the bearings in. Something like a hotshot front upright has 2 bearings very close together, so if you use close tolerance bearings, the bearing housings must be very well aligned or the shaft won't go through the bearings, or will be trying to twist the inner part of the bearing in relation to the out. So sometimes a bit of slop is necessary to allow for the imperfections in the manufacture of the bearing housings 

 

:)

 

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Just as an aside, I managed to reduce much of the alarming slop in my Bruiser's rear axle pinion shaft bearings by adding a shim behind the E-clip (still a tiny bit of clearance is left to avoid side-loading the bearings and prevent binding, however) and wrapping the outer diameter of the bearings in thin brass shim stock. Now the play is reduced down to what's in the bearings themselves and not them rocking around in the diecast axle housing halves. Livable for me now ;).

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