I'm in the process of rebuilding my engine. And my question is should I reuse my main and rotor bearings. I searched a lot on that subject and it seems to be better to use used bearings than new ones on a rotary engine.



On some bearing I can see a little copper, but not that much about 5-10 % of the bearing. Also I can see different gray color, some place it's light gray some other it's darker gray.



What do you think should I reuse them or replace them ?



Thanks for help guys!

It depends where and how much copper. On some bearings it's normal to see copper in a line where the bearing was locked together.



I've actually reused bearings that had a little copper showing because it was an NA engine for my own personal use. I also bumped up the oil pressure to like 90PSI. If it locks up, I've got nobody to blame but myself, although the likelyhood of that happening is quite low. It was a running engine before the rebuild (your basic apex seal swap with a port job), so uh, I'm ok with leaving the bearings as-is. It's still running just fine and lots better than before the rebuild.

can someone explain why the bearings are coated with the soft babbit and why using new ones may be a mistake in a rebuild? i know it would make for a longer break in period but any other reasons?

For the best bearings, they will be as far as is possible from the shaft they support in surface hardness.



So if you have a very high stress bearing interface, that is failing from overload, you could make the shaft harder, by gas nitriding of chroming or surface heat treating, Or, you could make the bearing softer by changing the overlay alloy and depth.



The Lead Indium alloy (the grey stuff) can be quite thick in low stress applications.



In the old days when everything was crap, you would clip on a steel mold onto a rod big end and pour in some babbitt from a collection of wrecked rods. Do the same for the rod cap. File them off flat. Bolt them together and stick them in a lathe and bore them out to just a hair short of the right size. Then fit them up and work the rod back and forth to make the high spots shine. Then take it off and use a bearing scraper the scrape off the high spots. In just two or three goes, a good mechanic could do a rod. I have a bearing scraper used for big diesel engines.



These are engines the have a steel door in the crank case beside each connecting rod. You let it cool off. undog the door, go inside and air jog the cylinder until

you can get at the rod cap. You take off the rod nuts with a hydraulic wrench and get a bunch of help lowering the cap onto the floor, so you can look at the bearing. See the high spot? Scrape it off. Put it back in.



If I see a shiny spot on a bearing, I take some old 400 wet or dry that has been in the cleaning tank for ages, and rub it against itself. That really takes the edge off of it. Wet the bearing with solvent and clean up the shiny area (reduce it height) with the paper. No problem. The rotary bearings are not highly stressed in normal operation. But since some insane people drive the things Mazda has used only a very thin layer of antimony on the copper support layer. Copper is a good base to plate to, and is quite a bit harder than the grey stuff. Older truck engines didn't even bother with the indium or antimony lead at all. You open the package, you got copper showing from new.



The soft stuff can move around under high stress. It has a very low melting point. It is at the very limit of performance when you scream the rotary. If the oil film breaks down and the bearing touches the crank, it's all over. The overly will move from one location and pile up in another shorting out the oil film in that location, and so on around the journal.



So you run more clearance for a thicker oil film. You run racing bearings that (A) have that extra clearance, and (B) have a thinner overly (less likely to move) and the stronger copper is closer to the surface. You run as high an oil pressure as you can come up with. The extra clearance (think of it as a hole in the bottom of a bucket) is like a bigger hole. So to maintain that thick oil film (keep the bucket full) you have to pour oil in faster.



When you go completely nuts and scream the engine for ridicules periods of time, The stock pump is discarded and a much larger displacement pump is installed outside the engine. The rotary has the rotor bearing mounted in the center of the piston, where the only cooling the bearing can get is from the lubricating oil. You have noticed that there is a pair of jets spraying extra oil into the center of the rotor once the engine is at speed. The only reason for this is to cool the rotor. The rotor gets hot and the bearing gets hot also. The cast iron rotor is in no danger, but the overheated bearing will leave the show early.



Notice that Paul Yaw cuts right to the chase, and bores away the indium and opens the bearing up into the copper. Harder bearing material, and a thicker oil film. All good stuff.



Look at www.yawpower.com Great tech section. Great pictures.



Now back to the questions.



I lost two store bought race engines almost back to back from bad rotor bearings.



They had plenty of clearance, and tons of oil pressure. we were not using the engines hard at all. The overlay just started moving around.

Mazda had changed suppliers to save money. Thank you bean counters.



So there is that aspect. If I have a bearing in a stationary gear that has been to 9,800 many times, with no problem, would I change the bearing just because the engine is in pieces? No way in hell will I do that. The bird in the hand solution.



You cannot just go on forever doing that, but it is a great general rule. Too much bearing clearance, makes for low oil pressure at low RPMs but for a nice fat oil film at speed.



The other advantage of a super soft overly is that small pieces of abrasive material that would otherwise damage the crank will just be pounded into the surface of the soft stuff to a point where it can no longer touch the crank.

Just like it wasn't there at all. So you could do 200,000 miles on that crank. A harder thinner overly, or just the copper may only go 100,000 miles.

Big deal. If the old bearing is not damaged, I use it over. I even press out race bearing from old rotors and press them into new rotors. You will see areas where the bearing, even new ones are showing copper when you open the box. Where the puzzel lock may move a bit, they cut away the indium in that area already.

Clean up any shiny spots with wet or dry in solvent. When you scream the engine, the crank takes on an "S" shape because the rotors are offset. So you will get a shiny band at each end of the stationary gear bearings. Just clean it up with paper and put them back in, so long as there is no other damage.

If you are not completely comfortable with anything, bearings or anything else. Just replace it. New parts failures are so rare as to be discounted.



Lynn E. Hanover

Wow, FANTASTIC reply Lynn.. Good grief, I didn't know someone could know that much. https://www.nopistons.com/forums/pub...IR#>/smile.png



I have one to toss at you.. something I've heard about before -- polishing gear and rotor bearings prior to pressing and being used in an engine. I'm not sure by how much but I understand that it would make for a flatter, more uniform surface as well as a slightly increased clearance between the bearing and journal. Whaddya think?



B

Wow, thats probably as complete an answer as anyone could ever hope for. https://www.nopistons.com/forums/pub...IR#>/bigok.gif

Thanks Lynn for the informative writeup. Much RESPECT.

This is not a bad idea. There is a chance that some flakes or burrs may be left behind during manufacture, and if the bearing has been pressed already, as when you buy a stationary gear. There may be some damage that could be repaired by polishing will some old wet or dry. (Silicone Carbide)



When you look over a bearing that has been pressed before you get to handle it, check that the tang has been centered up in the slot. Some are not square from the factory. When the misses the slot by a little bit, the bearing will be deformed right beside the slot. I give them a little scrape right there just to be sure that nothing touches the crank.



I have been grinding off the tab when installing racing rear stationary bearings.

The unit with the three windows. Also the rotor bearings. There is no relationship to be maintained, so the tab on the bearing serves no purpose. If the bearing fails and welds itself to the crank, the tab wont stop it from spinning in the rotor or stationary gear. The front stationary gear bearing must be indexed to align the oil hole, so leave that one alone. When you replace the front bearing, break out the die grinder and mate up the edges of the hole in the bearing with the oil gallery in the gear.



Never install a racing rear stationary gear bearing in a stock stationary gear. The racing (hardened) stationary gear has a groove machined in it through the oil gallery to feed the back side of that three window bearing. The damn thing still comes with the tang on it. The three window bearing can be installed in any position, because it is fed from the groove behind it. If you press it into a stock gear there is a great chance that you will cover up all or part of the oil gallery and loose the engine. The new gears come with the tab ground off, and a screw run through the bearing. To do what?







Lynn E. Hanover

I love your posts, You should start write up threads ala Judge ito to educate us all.

My rear stationary gear's oil hole was slightly offset from the 'gallery' so I dremeled it over a bit to match. Now you can actually see all the way down to the shaft when looking through the oil filter pedestal mount where before you'd see a nasty edge. Good advice.

The question still remains, at what point should you replace your bearings? How much copper is too much?

At $10 a bearing I would think any coper is too much. But I am on my first rotary rebuild. https://www.nopistons.com/forums/pub...R#>/unsure.png What ever happend to plastigate https://www.nopistons.com/forums/pub...#>/biggrin.png



Gregory

Did you fail to read those excellent posts by Lynn, or was it just past your comprehension?

That was a little rude. Perhaps you could answer his question, then.



B

pistons and connecting rod bearings dotn get along for some reason, i havent had a bearign problem yet with a rotary https://www.nopistons.com/forums/pub...IR#>/smile.png

"So there is that aspect. If I have a bearing in a stationary gear that has been to 9,800 many times, with no problem, would I change the bearing just because the engine is in pieces? No way in hell will I do that. The bird in the hand solution.



You cannot just go on forever doing that, but it is a great general rule. Too much bearing clearance, makes for low oil pressure at low RPMs but for a nice fat oil film at speed"



So please tell me how that is clear?

No one asked for a general idea of yea its ok, but AT what point is too much too much? Take a chill pill man.



But once again if the motor is out WHY NOT replace them? Is increased break-in time the only downside?

I read the post, comprehended it, and greatly thank Lynn for it. However, the question of "when" to replace has not been clearly answered.



Gregory

Little harsh? Sure. Out of place? Not to me.



I guess thinking for yourself is just a little too hard sometimes. From Lynns post, and common sense, its reasonable to assume that bearings should be replaced when the clearance is large enough to adversely affect the oil pressure. Thats the *need to be replaced* level. Anywhere between there and new is very subjective, and is totally up to the engine builder whether the bearings would be better off being replaced. One exception though would be abnormal wear. If there is abnormal, or excessive wear, it should be replaced. Anything else its more a matter of personal preference on how you want the clearances set in your engine. Thats a whole different subject though.



Lynn, how about a thread with your thoughts on engine clearancing? I would love to read that, as Im sure many people here would.

All copper is not too much. Machining away all of the overlay is a method of increasing oil film depth and adding a pit of room for the sine wave shape of the crank. So when you scream the engine, and the crank bends a bit you don't skin up the ends of the main bearings.



It would take so long, and so many starts to were away a large amount of overly in normal operation, that large unclad areas would indicate replacement just for

fatigue breakdown would be in order. If you see small cracks forming in the overlay so it looks like the drying mud in a puddle indicates long term stress breakdown. But that takes a long period of abuse.



So if overly is missing from street run bearings, it is usually time based, since the wear comes from cold startup with no oil pressure, and to a lesser extent acid attack from never changing the oil. Copper showing in that case would require new bearings. If overlay is missing from any location on a street bearing, other than across the puzzle lock, pitch the bearing.



Lynn E. Hanover

Ok now that makes sense. Now I just need that tool to measure the bearing diameter...

Wow! A lot of posts. Thanks all! I will check them carefully but I don't think I will have to change them.

Just wondering that you guys think. My main bearing are showing about 15% copper on the front upper right side of the front bearing, and the rear lower left side of the rear bearing (looks to be inline with the water pump so i think the previous owner may have tightend it to much, thus wearing the bearing in thoose areas at startup. The front bearing also has a few (3-4) scratches in it down to the copper, like something small went through it, the scratches are small, bout half an inch long and just deep enough to barley catch a nail on them. I was going to replace these bearings but after reading this, and talking with the machine shop i was going to have them pressed in at (they said they looked ok) i might just polish them up a little and use them. Whats everyones opinion? I'll try to get pictures, but my friend has the (crappy) digi cam right now, but ill hopefully get it back this week.

Read above. Uneven wear is never good. If you dont mind the loose clearances, and have an oil system than can support it(the n/a pump cant), you can do like Lynn recommends and take the whole bearing down to the copper. If not, you should replace them.

Thank you for the reply. I did read it, im more worried about the scratches as i can even it out with sand paper as suggested.. a T2 pump is planned in the near future, till then i dont mind it running low at idle. I think im going to go ahead and change them though,.. but i'm still not sure. this is gettign expencive fast and saving another 40 bux (bearings + pressing) would really help out, but not if its going to cost me the motor.

Welcome to the wonderful world of building engines. Im still recovering from the last engine I built...

Lynn, Would the MFR bearings have less of this "overlay" when compared to the REW bearings?

REW bearings have more clearance than the MFR bearings.

I shine them up with 600 or killed 400 in the cleaning tank. The picture is of such a bearing. Note that the overlay is so thin that you can se the copper through it in places. Note also the copper showing in the puzzle lock area.That is normal. If it is not gouged or melted in places, or have dirt welded to it in places, I would say leave it alone. If it shines up quick when you start, it is OK. Any other situation, press in new bearings.





Lynn E. Hanover

Yes, weve established that on a previous thread. Im still trying to figure out the advantages to the Mazda Factory Race bearings, if any. If it has less of this soft "overlay" material, it would ba at an advantage over the REW in a high output engine... theoreticaly.

Lynn, do you just use your finger on the paper to polish the bearings, or a sanding block or what?

i think lynn sands the breaings down to get the clearance down before he starts racing, if you break the motor in properly u wont need ot do this. correct me if i am wrong lynn.

Ok, I missed the point.



I do not know if there is less overlay on the race bearings. It never occured to me to think about that. I suspect that the same thickness is on both bearings. The race bearings are only .0005" larger in diameter than stock. The overlay is a flash plating operation, to keep thickness uniform. So lets just say it is the same thickness.



The thicker oil film is an advantage only at very high output. I raced with stock bearings for years, and after each teardown I would see shiny spots and rings around the ends of the stationary gear bearings. I would sand these off gently and go again. Once the overlay was very thin in most places, and missing around the ends. There would be no further problems. So I am thinking that the overly was about .0005 thick to start. Now I can put in new stationary gear bearings and just sand around the very ends of the shell and a bit where they bend the tang out, and they work just fine. Usually they look the same at the end of the year as they did going in.



The bearing in the picture had two years on it and was going in for this rebuild just as you see it. I don't try to reduce the overlay on race bearings. Just at the ends where they will scuff a bit on a missed gear, and at the tang. It tends to deform a bit when they bend it. Note that the front bearing tang is left on the bearing. There is just one oil gallery hole in the front bearing, and it must be indexed to line up properly.



Just solvent in the cleaning tank and you fingers for a few seconds to but that bright shine back on the surface is all it takes.



If I say that race bearings are not required on the street, then tonight there will be a missed shift in Pomona and a nastygram about it Thursday. If I say that they should be used on the street there will be 100 nastygrams that complain about the oil idiot light coming on at stop lights.



Higher oil pressure does two important things at once. It increases the hydraulic pressure around the bearing and helps keep a high pressure wedge between the bearing and the crank. It also increases flow rate, so that superheated oil is being flushed from the bearing so it cannot overheat the bearing material. I have an external pump to do this, but the stock pump can do some of it also. I like 90-95 pounds. Racing beat says a top of 115 pounds. That seems a bit high to me, but too much oil pressure is like too much money. The people that have it seldom complain.





Also, keep in mind that even though the bearing sizes are the same, all that 13B stuff weighs a lot more than 12A stuff, so a missed shift by my driver may be just a driving error for me. It can be a disaster for you. A little money now for a rev limiter can save a huge amount of money later.



I kind of like the sound of the limiter going off. It means he is going through peak power before the shift.



Lynn E. Hanover

that funny that you mention that, building a f-atl Toyota 4AG (or whatever its called now) motor today i had the #3 rod give me totally non-linear clearancing, there was a little piece of **** burr on the bearings backside that would more around as i would clamp the rod up. drove me nuts for 15 minutes. I always use a little nail file that you buy at a drug store to de-burr all my bearings, piston or no piston motor.







-nick the racing idiot

Thank you. I'm definatly replacing them.