I am rebuilding an s5 turbo engine. Both the the stationary gears have copper showing on the outside part of the bearing. Does anyone have an explanation for that wear pattern? It is only on the outside half of the bearing, not the inside half.

I'll try to post pictures tomorrow.

 

I've never been one to rely on these things, but:

 

think about which way everything faces when the spark plug fires...

 

Please see the following pictures on my dropbox:

https://www.dropbox.com/s/8hds0t6eul...06.55.jpg?dl=0
https://www.dropbox.com/s/1gmnpwsqjd...06.59.jpg?dl=0
https://www.dropbox.com/s/of6ufgl9sy...07.07.jpg?dl=0
https://www.dropbox.com/s/u1jtqaalgz...07.40.jpg?dl=0
https://www.dropbox.com/s/kutta81xt0...07.53.jpg?dl=0

 

I'm not understanding what you're trying to hint at. Please just tell me if you know what could cause this sort of wear pattern.

 

He's trying to tell you that the bearing will be loaded unevenly because the crank is in the same general range of degrees at intake/compression/power/exhaust relative to the bearing on every stroke. It's unevenly loaded.

That said, I don't know that that's what's going on. Is that the front or rear?

It looks like that car probably sat for a good amount of time without running; is that correct?

 

That might explain why there is copper showing on only so many degrees out of the 360, but not why it only shows up on the outer part of the bearing.

The pictures include both stationary bearings, I'm not sure which is which now.

The engine sat for almost two years in my basement, unknown how long it sat in the shop of the person I bought it from.

 

Is it the outer half of both bearings? One side has the flywheel assembly and transmits all the rotational energy, and the other gets the counterweight and accessories and can be subjected to uneven wear from too much belt tension. If it's only on the front, I would suspect the belt tension scenario. If both, I would suspect crank flex combined with the selective loading from the inherent geometry of a rotary engine and take a closer look at the middle one.

It looks in the photos like some of the surface plating on the bearing face has flaked off. I've only seen that one time before in an engine that sat for ~20 years. It's the result of oxidation from all the oil running down and leaving the bearing exposed to air after the finished surface has been compromised from use. It's obviously not a good thing, and it would cause me to pay extra close attention to anything above the oil line for corrosion. In fact, looking back at the photos, there's quite a bit of rust visible...

 

Yes, it is both stationary gear bearings. I have talked to a couple different people who have rebuilt many rotary engines, and none of them have seen this before.

 

One looks way worse than the other. Which one was that? Also, there's an indexing pin; see what direction the wear is relative to the engine. Up is different from 9 o'clock (looking from the front).

Also, what's the bearing in the middle look like? How's the play relative to the crank?

 

If you are worried, replace the bearings. $30 each at Mazda and easily pressed in by a machine shop paid in a 6 pack.

Or that said, I have see a LOT of engines run for YEARS assembled with copper showing on the bearings.

 

Ignore my asking about the middle bearing. There is no middle bearing. Too many engines laying around in my head.

The question as to which direction the wear is relative to the indexing pin is still very much in play.

If the question is whether or not you should replace the bearing while you're rebuilding the engine and have it apart to the extent you do, absolutely. It's cheap and you're already there. If the question is more a matter of why it's like that in order to be sure some fault isn't rebuild back into the engine... That still bears looking into.

 

its a pretty normal wear pattern. the FD had a little more clearance on the ends of the eshaft, so in theory it wears a little more evenly

 

Looks like either your bearing(s) and/or journals(s) are out-of-round. Have a reputable machine shop install new bearing and check bearings/journals for roundness.

 

I don't think it's out of round or the bearing would be worn all the way around on the one side. The e-shaft flexes since there isn't any bearing support in the middle, thus why j9fd3s said "think about which way everything faces when the spark plug fires". When combustion occurs, torque twists the e-shaft and at the same time causing it to flex ever so minute along its center line. It's a plain bearing so "technically" metal on metal contact never really happens (starting doesn't count) but the force applied to the e-shaft during combustion tries to squeeze the oil out of the bearing on one side. The metal might not be touching, but it is squeezing the oil out with extreme force and that oil has **** in it. Oil picks up **** very quick and those abrasive particles are being squeezed at the same time causing wear.

The pictures you posted are text book normal bearing wear. If you where to look at a piston engine bearing for example, you'd see the babbit gone and copper showing closest to the piston rod. Why? Same thing I mentioned before about extreme pressure being applied to the bearing and oil being squeezed out.

And if you don't believe me...

Get a piece of steel that isnt rusted and coat it in oil. Drill a hole in a penny and attach it to a dremel. Spin the dremel up to 2,000rpm and then press that spinning penny against that nicely oiled piece of steel and time how long it takes for the copper to be gone and the silvery zinc to appear. It won't take long at all.

 

Make sure the penny is post 1982.

 

I'm more curious about the cause of the pattern and if it's something to be concerned about. I will be replacing the bearings because they are cheap. Thanks to Aaron Cake for letting me know that they would be reuseable, I was curious about that, but I might as well just replace them to be on the safe side.

 

This is sort of what I was thinking, especially if this was combined with insufficient oiling at high rpm.