In my experience with sleeve bearings... not sure if they operate exactly the same journal bearings... but sleeve bearings are cheap to buy and they are just press fit into the hole that you need a rotational connection. After pressing the part, they usually need to be reamed out to tolerance... anyway... I'm guess the bearing is needed because a different material is better for teh bearing surface... when you purchase them, they have all sorts of different materials with different specifications... viscosity ratings.. and this and that... one of the more important ones is simply... longevity of the bearing... and it depends on a lot of factors.. such as temperature... avg velocity of shaft... and all sorts of stuff like that...

perhaps the rotors expand a little or contract a little when at running temperature.. and a bearing material is chosen that will expand and contract at opposite rate.. to maintain a uniform bearing sleeve size...

other bearings have properties that keep oil on the bearing surface..

 

What about the issue of overhaul? I always thought that was the idea behind replaceable bearing inserts. If you were to rely on machined block for bearing, what would you do when it was worn out of spec? The practical answer would seem to be -- use a bearing insert!

 

This is a bit out of topic but related, if turbo with bearings has less turbo lag due to less slowing down of the turbine. Is it the same here in a rotary engine???

 

Turbos utilize a different bearing.

 

If the bearings fails you replace them, and the e-shaft, if a bearingless engine fails you replace the engine, got it? money wise? please let keep the old trusty cheapie bearing
alive.

 

Actually when a bearing fails in a rotary, you are still replacing alot of big parts. This may include the eccentic shaft and stationary gears at the least but probably rotors and housings as well.

 

I've recently been informed that if we didn't have bearings, we wouldn't know which way we were going. Now that makes sense!