Thoughts on Repalcement bearings ?

OEM every time.

Most OEM bearings in Japanese bikes are either Koyo, NTN or NACHI. In the Euro bikes you may also get FAG or SKF.

It is possible to buy these bearings cheaper than the OEM prices, but you have to do some research and find a supplier. We use a mix of OEM or, the correct spec branded bearings in our builds.

As an example, all Honda CR250's use 63/28C3 main bearings. From Honda there are around 10 different part numbers for these bearings depending on which year you look at. They range in price from around £15 to £30 each, depending on which part number you order.... Which ever part number you order the packet will contain the same KOYO 63/28C3 bearing...

Ceramic bearings are incredible... but they are also incredibly expensive. IMO it's not really worth the extra outlay. For a factory race team? Yes, every possible advantage must be taken... but for a "normal" guy, it's a waste of money. I also read somewhere that they don't really have much an advantage over the std type bearings until they are running up around 20,000 RPM..... Not sure how correct that is though.

Stevie

I had bought some aftermarket bearing and seal kits from a online bearing vendor and ended up with crank bearings that were too wide by a few thousandths. Just enough to put the crank in a bind when the case halves were torqued down. So pay close attention to what you get. Someone else here mentioned their transmission not spinning when assembling the engine with aftermarkets bearings so may have been the same issue. Here is what I have been running in my old high compression 74 CR250 for crank and countershaft . Also some good info in the thread.

http://www.vitalmx.com/forums/Moto-Related,20/Crank-bearings-engine-gur…

The only the you need ceramic bearings is in Heavy motors running huge air handles and such, due to current leakage. We use the SKF brand in all our heavy applications. I have read where they use the FAG bearings in TZ 750's and get another 300 rpm, believe they are German made

In the engine I only use OEM but I will use All Balls kits on my wheels because sometimes they're easier to find in a complete kit.

Not sure why, but I bought a set of OEM Yamaha main bearings for my 1979 YZ250 engine years ago. They had a plastic type of bearing cage / ball separator, not steel. Old tech ?

Needless to say , I got about 15 races out of them before the plastic cage broke off in the ignition side bearing, basically loosing crank timing. Gave a big backfire and rolled off the side of the track, dead.

Went to the bearing house and got some good C3 bearings. Plastic in a bearing ???

I use top quality on the crank, and always metal cage, SKF Fafnir, Koyo, FAG,, the rest I get from my local supplier,, medium grade middle of the road, Never China, never plastic cages.

Plastic cages are bad? How about those metal cages that are riveted together when the cage cracks at the rivets and pieces of shrapnel go through the crank and transfers ending up on top of the piston beating into the head? Yep, seen that more than once.

Plastic or steel cages mean absolutely nothing. I work with Rotax engines every day, in the sleds the 800Etec engines put out close to 170hp and they are plastic caged bearings. Out 600etc engine put out a little over 120hp and I have seen many with more than 12,000 miles with out an issue of any kind in the engine...again BRP has been using plastic caged bearings for well over 20 years. I much prefer plastic cages, If you have a bearing failure you will have less debris showering the rest of that cylinder......I have seem many times much more damage from failure of a steel caged bearing.