FD3S_wanted

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!

Jeff20B

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.

BigTurbo74

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?

Lynn E. Hanover

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

BDC

Wow, FANTASTIC reply Lynn.. Good grief, I didn't know someone could know that much.



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

CGeek2k

Wow, thats probably as complete an answer as anyone could ever hope for.

boost_creep

Thanks Lynn for the informative writeup. Much RESPECT.

Lynn E. Hanover

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

Drago86

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

Jeff20B

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.