Can anyone tell me what ABEC ratings are the best for engine bearings?

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The Best !!!???
It all depends on what you define as the best.
Here are the out of centricity data of some abex grades[*]ABEC3: 0.005 mm (0.000197")[*]ABEC5: 0.0035 mm (0.000138")[*]ABEC7: 0.0025 mm (0.000098")[*]ABEC9: 0.0012 mm (0.000047")

ABEC 5 would be a good smooth quality bearing. In most engines a #3 bearing would be excellent value.
ABEC 9 would be prohibiting in cost, but obviously better than the #5 bearing. Your engine however would not run better with it, unless you want to run it at 40,000 rpm</p>

Tight tollerences are not always the best thing for engine bearings.
Check out http://www.rc-bearings.com he's got a lot of info and is happy to answer bearing questions.

I wouldn't worry about the ABEC ratings if you are buying from a known vendor like RC-Bearings or Boca.  it's just not a critical item in an RC plane, espcially when you can re-bearing a plane for under $15 for bearings, delivered to your home.

jack

ABEC-3 are just about the best combination of quality and cost. Going better than that is wasting money unless you can get them for the same price. Many of my bearing suppliers aim for ABEC-5 in normal production and I get them for the same price as ABEC-3.