Where to Buy Ball Bearings
 

I have an HP .21 4-stroke that needs ball bearings. What brand is best and where is the best place to buy them?

Boca Bearings!
 

This is the best company around to get your bearings for any engine.

http://www.bocabearings.com/

Where to Buy Ball Bearings
 

Just look up bearings in the phone book. Phone a company and tell them the I.D., O.D., and width and if it has seals or shields, etc. They will give you a standard part number and a price. The bearings in most model airplane engines are really worth about $5. Almost all bearings are made by a few companies, NTN, SKF, FAG, Fafnir, Tinken, and a few others. They are made to industry standards. Class 1 and 3 are considered commodity grade, class 5 and 7 are considered precision, and class 9 is ultra precision - instrument grade.

Good luck.

Where to Buy Ball Bearings
 

So which class would be best for a plane engine? Commodity or precision?

Where to Buy Ball Bearings
 

Usually when you take it out you will see that it is one of the above mentioned manufacturers and will have a part number.

Most of the bearing places have books which list all the numbers
as well as crossreference between different manufacturers.

Where to Buy Ball Bearings
 

I don't know exactly what your motor came with, but I bet it was a class 5 ball bearing. BTW, it does not matter which company actually built the bearing. They all compete for the same standard sizes and applications. Your bearing supplier will probably not even tel you who makes the bearing unless you specifically ask.

One of the products my employer makes uses a 12mm ID x 28mm OD bell bearing. It only costs us $.90 in quantity. The same bearing can be bought over-the-counter for about $2. It's class 3.