Attn Engine Builders, Do You Re-Use Main Bearings and/or Rotor Bearings?
 

I re-used main bearings (in good condition) in my latest build, but the UOA is showing quite high copper and lead, indicating bearing wear. You rarely hear of bearing failure in these engines, but wanted ot get 0.02 from some of the members who regularly tear these motors down. Are race bearings a worthwhile investment for higher hp engines?

rotor and stationary gear bearings are usually reused unless they look damaged. How did they look? Bearings don't just fail because they were reused, there may be something else going on.

Probably from under-utilizing that heavy weighted oil you keep using. :p:

In my limited experience... The last couple engines i put together, i used one of these on the bearings:

http://www.penntoolco.com/images/catalog/5936.gif

Despite the babbit (silvery) coating being depleted in some locations, they were still well in spec although bronze was showing. Talking to more experienced builders, the risk of a spun bearing increases with bearing replacement. Therefore, bearing replacement should be performed on a need-to basis. That's my understanding and also what I practice when I get the chance.

it's on now, another oil thread :lol:

I was running 20w-50 in the dead of winter for awhile there, that may have contributed to some excess wear at start-up, but my engine builder doesn't think that's it. I'm running Shell Rotella 15w-40 now so I'll see how the next UOA looks.

Interesting.

Who states that the risk of a spun bearing increases with replacement? Maybe if you install them incorrectly.

We install new bearings in the majority of builds, I feel that it's an integral part of a 'new' rebuilt engine. I'm of the belief that many don't want to do it because it can be a bit of a pain in the ass.

Anecdotal, but a good friend of mine had his original engine rebuilt at approx 65k miles. It died from coolant seal failure. His engine builder recommended leaving the bearings alone..... 25k miles later, he spun a bearing during normal driving and lunched the whole engine. Always changed the oil at 2000ish miles, never ran the car hot or abused it.

When my engine was reassembled I had the attitude of "while you are in there". You are better off replacing them now instead of having a possible issue down the road, just one less thing you have to worry about.

^+1 this guy is right while you are in there you should replace them all

This doesn't make me feel too good. I'll keep an eye on the UOAs to see if the problem gets worse.

On a street rotary, there is absolutely no reason to replace rotary engine bearings if they are with-in spec. They can be reused. They will last well past 100,000 miles. Most don't realize the rotary stationary gears absorb a lot of the rotational load. The bearings mainly get damaged when the apex seals break. The debris from the apex seal causes the rotor to jam heavily against the e-shaft (which makes the rotating assembly move. If someone is spinning bearings or is showing excessive copper, then they have an oil pressure problem. I've seen some really shitty oil pumps that people re-used but never spec them.

New main and rotor bearings increase the break in time. Rarely are they out of spec, when they are we replace them. Using the bearings that have already been broken in to the eshaft is preferred.

Mazdaspeed Tech

"Check for abnormal abrasions or signs of flaking or seizing. The bearing should be replaced if flaking is evident over one-half of its total area. If the old bearing does not have any excessive wear, reuse it, as an old bearing is generally preferred over a new one."

Different folks different strokes I guess, or maybe I should be more careful who I listen too :). Either way, I'd never replace one that doesn't need it. You're absolutely right, it's a pain in the ass... not gonna go through that unless it will have a distinct benefit.

Pain in the ass? I've never had problems changing any rotary bearing. Hell I used the front pulley boss for the rotor bearing. Perfect fit!

I'm surprised that an old bearing would be preferred.

Log on to http://www.mazdamotorsports.com and go to the tech section read all the info for yourself.

http://www.mazdamotorsports.com/weba...t=rotorbearing

As far as bearings being difficult to remove that is incorrect. It is a 1/2 hour job at best to replace the two rotor and two main bearings. A simple press and the bearing tools are required. I would say that removing the set screws in the stationary gears can be the biggest PIA, as they are soft metal and are thread locked in place. We install new sets screws whenever bearings are replaced.

There is also a chart there that shows the recommended break-in is 3x longer with new bearings installed

If a customer comes to me and wants a reliable, long-lasting rebuild for a street car and has the original (almost 20 year old) bearings in the engine then we replace them, case closed.

A longer break-in period isn't reason *not* to do it IMO.

I've also seen many first-time bearing installs go awry, typically the rotor bearings get mis-aligned. We don't have these problems b/c we do them on every build, but it can be a steep learning curve for the non-experts. The prodigies like t-von notwithstanding of course :lol:

Everyone has their own opinions on the subject, that's mine..... I guess we'll all have to make our own decisions and go to our own church, right Mark? ;)

Most FDs nowadays are in the 100k+ club.

Dave

You can argue all you want.

Facts are Mazda does not recommend replacement unless the bearings are out of spec. Never said longer break in was a reason "not" to do it, simply stated this is another drawback. Not to mention the unnecessary increased cost added to the build

Also 17 is not almost 20, there are a lot of 17yos that would love it if it were the case, then they would not be 4 years from "bar" age.

I'm not arguing with you Chris.... I'm stating my opinion and practice, just as you did. That's the beauty of a public forum. Let the masses read all of this and form their own opinion.

As far as added cost, we perform the service free as part of the build. Parts costs are negligible, much less than apex seals for example.

Again, this statement is not aimed at you or your shop, it's a general statement-------> Do it once, do it right. For original and/or high mileage bearings, if I'm in there anyway I'm going to replace them and be done with it.

As I already mentioned in my last post, to each their own. Have a great weekend everyone :)

Well then you can come do mine next time :) Yeah, you have the recessed set screws, alignment marks to make... why do all that if there is no benefit is all I'm saying. Regardless, some people do so with excellent results so more power to them.

The way i undertand it is this: Since these are hydrodynamic bearings you want a certain thickness of lubricant flowing between the journal and bearing surfaces. On older, broken in bearings, that clearance is more even across the geometry and closer to ideal conditions. This makes the lubricant film more even and reduces thin spots that create what is called boundary layer lubrication (only a couple of molecules thick), ultimately reducing friction.

it can be reused unless showing copper, with the very few engines that ive helped Zavier put together i know that we dont like using any that are showing copper but a little is okay.

lol, ummmmmm so hey guys I'm rebuilding an engine and one of the apex seals has a hairline crack, it's ok to re-use right?