bad rotor bearings?
 

My mechanic said that I need new rotor bearings since they are worn down to wear copper is starting to show. I took a look and he is right but is this normal? I asked around and most people said that rotor bearings don't usually need replaced during a rebuild.

Most builders reuse them even after 100k miles. Last I heard, general consensus among many that less than 40% copper was useable. My personal limit is about 25% copper showing. IT is perfectly normal for copper to begin to show through in a spot here or there 1/2" at a time.

At $35/pair, its cheap insurance to simply replace them, is it not?

Ya, I ordered new ones. The engine is apart so no reason not to really. Was just wondering since everyone said how they don't need replaced.

Not necessarily, here is why.

For most cases, especially DIY rebuilds, it is difficult to properly press out originals and press in replacements. Bearings are very soft, and warp/marr easily. Since the tab has to be perfectly lined up, it is very easy to screw the job up.

Rotors are also fairly soft. It is the opinion of some respected builders that you can actually remove some material from the rotor while pressing in/out bearings. This could result in a less than perfect fit on the new one, promoting bearing spin and failed engines.

Rotary oiling systems are very good from the factory, almost as good as many race engines. IN my personal rebuilding/core disassembling experience, less than 3% of rotary bearings show more than 10% wear, even after 150k miles. IN other words, rarely is there anything wrong with what you have.

IN breaking in an engine, there is merit given to the idea of heat cycling on metal parts. Since original bearings have been cycled thousands of times, they are thought to be stronger and more reliable than replacements.

IF you are using the same eccentric shaft, rotors, and stationary gears in your rebuild, the rotating assembly is already broken in to each other, why would you disturb this?

I would like to see pics of these "worn" bearings. Worn bearings could imply something wrong with the engine - even high mileage rotary engines should not be wearing rotor bearings out.


-Ted

There is just the slightest bit of copper showing. He really likes to replace everything just about. He said he'd reuse them if I wanted, but I figured since they aren't too much money I would just buy them.

I would replace a bearing that is out of spec and showing copper wear. Installing new bearings is not all that difficult if you have the proper tools.
Heat cycling will occur during break-in just as effectively as it did during the first break-in of the engine.

if it aint broke(or going to brake, or slowing you down) dont fix it

Since you have the new bearings.......install them. But if you will read the Racing Beat catalog where they state: All rotor bearings, stock or Mazda factoruy Race, are made from a flat piece of steel which is stamped, rolled, and hooked togethre at the joint with a *puzzle lock* design. This bearing is then coated with copper and plated with about .0015 inchof BAbbittl bearing material. The inside surface of the puzzle lock joint area is ground off to eliminate high spots., usuall resutling in a portion of the copper coating being exposed. This appears, to the untrained eye, to be a worn spot ont he bearing, but is in fact normal.

Well I already ordered new bearings, so when I get them I will compare and see.

well there should be a small area of the copper showing thats the joint where it was welded together and it comes from the factory that way

I was just going to mention that...
If you see a "worn" spot that's about 1/4" and goes across the bearing axially (from one hole to the other hole), it's NORMAL.

Breaking in new bearings is a pain in the ass, and your mechanic needs to be educated of what these rotary engines bearings should and should not look like. He could be reaming you for unnecessary work - unless you like paying for work that's not necessary...


-Ted

Its the same price. He isn't charging me for anything extra while the motor is out. If I buy it, he will put it on at no extra cost.

All ways take precautions when breaking in new bearings. They are much more sensitive to clearance. If you run out you are fucked. Most of the time it is not needed to replace them, if you do chances are there are other problems. But if your mechanic is used to rod bearings then I can see why he recommended you to have them replaced.

whos rebuilding your motor...scott over here in St. Pete?

No, a guy I know named Sam.