What would cause the rotor to make contact with the irons? It happened on my rebuild with 300 miles on it. I heard it starting to knock and the motor was shaking violently. I tore it down again and after inspection of the motor it looks like the rear rotor bearing moved a few degrees. The bearing started to back out of the rotor and the rotor made contact with the intermediate plate which flattened one of my side seals which caused it to lose compression. It was actually sitting flush in the groove with rotor. Anyways I think I caught it in time to save my motor. Does this make any sense?

Thanks, Ed

 

I follow ya. I've heard two things about bearings: .005 diff, or a .001 or .002 "taper" in the bearings (one side .004 and the other .005 or .006). This was stated in the "Competition Manual" which you can find in a thread in the race section.

Just out of curiousity, what was the e-shaft float when you put it together? Don't worry about being exact... I rarely write that stuff down (but I should) just curious if it was in spec and how far in.

 

As far as I can remember that shaft was good. The motor was a smoker. This was the reason for the rebuild. Anyone ever replace bearings before?

Thanks, Ed

 

The shaft can be good and the float still be out of whack. The spacer you put on the front that the needle bearings ride on is what controls it. If you built it by the book, it tells you to check the float of the e-shaft before you put the cover on. I forget what it allows, but it's a fair amount. Too much would certainly cause that.

The smoking is probably from an oil seal. The one I just built did that... haven't taken it back apart yet, though.

 

My first rebuild did the same thing, but I was on track when it happened and wiped out the bearing and the rotor and eshaft. End play was well within spec. I still dont know why it happened. Bearing seized to shaft and spun and locked on the shaft and galled it all up best as I can figure. I guessed oil starvation, and the bearings were used, in spec ones already in the rotors. No major over revving, maybe to 9k when necessary to save a shift here and there.

 

Chris, the end play was good.
Carl, I think over revving is what did it to mine as well. I cant think of anything else.
Needless to say I need a new bearing pressed ino the the rear rotor. Whats the best way to do it?

Thanks, Ed

 

Use the tool from RB or Mazdatrix. Those are big bearings.

 

Thanks Carl! I'll check it out.


Ed

 

13Btoy, To remove those bearings heat the rotors in the over to around 400 degrees then throw em on a cookie sheet and head to the garage. Get some oven mitts and then press out the old bearings. If you dont have a press buy one. When you install the new bearings get some lock tite sleeve ratainer heat the rotors again..apply the sleeve ratainer the the bearing line it up very carefully and press it in. I do this without the mazda tool but I've done many sets...you may want the tool depending on your meachanical ability. Any good garage should also be able to do this for you but they usually wont take the time and effort with pre heating and the locktite. If you ever see the book How to modify your RX-7 buy it think you would enjoy it and your next engine would be trouble free. Check ebay for the book and good luck its out of print. Hope I helped,Custom13B

 

Custom13B, thanks for the info. I actually have this book. Anyways how much copper should be on the bearing to be determine it bad?

Thanks, Ed

 

Ed, A good bearing shows no copper. There babbit bearings and are made of copper then there is a lead colored coating of another material over the copper. On these bearings there is a small section thats not lead plated even when new. Its part of the manufacturing process. Dig out your how to modify book and check page 96 for the bearing specs. I highly doubt your e shaft is too worn. If you like to be 100% like me you can buy a cheap set of micrometers and measure it. Again JLindustrialtools.com or harbor freight.com. I baught a 0 to 6 inch set for like 60.00 yea thier chinese but are more than accurate enough for this. Any rotary I rebuild gets new stock bearings. They are cheap. My first rebuild I reused the bearings and had too much clearance so learned my lesson. If your building it for racing check out RB's race bearings. Or look on page 77 of your book. Also in that book is the side seal clearance 1.8 thousandths is correct..my factory service manual states 18 thousandths and that cost me a second tear down. Ttyl,custom13B

 

I highly prefer proven, used bearings within specs, to new, unproven bearings. I really don't care what color they show as long as they are still round, smooth, and within spec.

Clearance on rotor bearings is 16 to 31 ten-thousandths of an inch (0.04~0.08 mm). The eccentric shaft end play clearance is very little (you should have a dial indicator to measure this properly) at 16 to 28 ten-thousandths of an inch (0.04~0.07 mm).

An over-rev alone can throw the rotor into the side housing (and is THE most likely cause), not to mention along with end play out of spec. The bearing probably moved when the rotor hit the housing, not the other way around.

 

nimrodTT, so you think that the end play caused the problem?

Thanks, Ed

 

It's possible it contributed, but with the info you've posted so far, I think it was the over-revving. How high were you revving, and what was your end play at?