R.P.M.

OK guys,



When using New OEM bearings from Mazda, what do you do to clearance the bearings to the e-shaft?



I've heard of guys doing nothing to them, using the right oil and breaking in the engine for a longer period of time and having no problems with them. (I've done this several times with no problems) (Just finished a 400whp FD that makes all kinds of oil pressure after beating it up for hours)



Others machine the bearings with a lathe after pressing them into the rotor or stat gear and clearance them to the OD of the e-shaft.



Others hand sand them with 600 grit paper...which really scares the **** outta me because how would you ever get it even close to round?



Also what would you normally clearance them to? 2 thou seems to be a pretty decent clearance.



Just want to get other builders opinion on this.



Thanks

j9fd3s

yeah the hand sending thing is out....



i would just start it and break it in nicely, although thats kind of taking mazdas word for it

Lynn E. Hanover

Hand sanding works great. 600 wet or dry paper is just fine.



Or you could buy the racing bearings, but they only give you .005" more clearance.



Or, you can bore out the bearing hole in the rotor, then bolt the bearing in place because there will be little crush fit.



Lynn E. Hanover

R.P.M.

You mean 0.0005"



5 thou extra clearance would be a bit much

C. Ludwig

You can also work the e-shaft down in size to fit. Good excuse to polish the journals and true them up.

Lynn E. Hanover

You are correct. That should have been .0005”. Or, five ten thousandths. Or one half of one thousandth.

Sorry about that.



The object of increasing running clearance is to increase the volume and speed of oil moving off of the bearing. This keeps the bearing from overheating due to increased loading.



This is also why it is advisable to increase oil pressure when higher output is expected.



If there is a plan to increase clearance by machining away the Antimony layer (the gray stuff) thus leaving the copper as the bearing material. Do this with the bearing pressed into a rotor. This will hold the bearing in a round condition, which is not always the case for the loose bearing.



The race bearings used to be made from a piece of tubing, where the stock bearings were bits of sheet stock stuck together with a puzzle lock. Guess which one was round while still in the box.



I don't know if this is still the case as I have not replaced a bearing in years. Use a racing synthetic and at least 100 PSI of oil pressure and you won't either.



If you run on the copper, you have removed about an additional .001” to .0015” from the bearing (about the thickness of the Antimony).



This is not as crazy as it sounds at first. This allows for more crank flex without bearing damage, and if you plan to scream the engine a good move. Running on the copper is not a bad idea at all. Copper is stiffer than Antimony and does not flow away from high load areas. I overhauled an old Ford “Y” block truck engine once, and took the old bearings to the NAPA to show them the part numbers on the backs of the bearings and the fact that they were all warn down to the copper. The old guy just chuckled and gave me the new bearings, with the bright shiny copper surfaces. Duh????????



You can also bore out the bearing hole in the rotor until the crush fit is nearly gone, and then drill and tap three holes on each side and bolt in the bearing with six screws and Locktite. If you pick up a set of rotors with the bearings bolted in, it is likely that this has been done, and a new bearing will need the same screws to hold the new bearing in place.



The idea of sanding off the Antimony to gain clearance, is no less valid than any other method of doing the same thing. I have a bearing scraper for locomotive bearings. I have seen Babbit bearings poured right on the crank. I have saved race weekends for folks by scraping half a set of .010” under rod bearings for a Spitfire back to standard. Moved a crank forward in a rotary by putting a beer carton spacer under the front stationary gear. This got the rear main bearing off of the crank radius in a short engine. I know what its like to want to race and have no money at all. To work on cars with a hatchet and a rusty pair of pliers. Hang in there. It gets way better.



Lynn E. Hanover



I am working on a piece about laying out port timing. This JPG will be part of that.

Old Grey

I'm not a big fan of removing the crush and then grub screwing the bearings. If the bearing rotates just a little it will roll up the grub screws clapping the crank solid.



The old way to clearance bearings was to tape a strip of wet and dry to a die grinder tip and spin it in the bearing but using just the tip of the W&D. The one strip flaps out like a propeller so the tip gently brushes the bearing. The problem is it's easy to over do the edges compared to the middle.



After I started modifying the oil galleries and bumping oil pressure up to 86psi, std clearances were OK for 500rwhp street engines.

Lynn E. Hanover

These would be flat headed socket screws through the face of the bearing in a raidial pattern. As seen in racing engines from major builders. One who builds all of the engines for the "Formula Mazda" series.



http://www.starmazda.com/



My personal best has been over 13,000 RPM. Driver got 1st looking for 3rd. Stuck the corner seals, but didn't hurt the bearings. That rotor and bearing ran again the next day. Bolting the bearing is a very good option when increasing clearance.



Lynn E. Hanover

Kyrasis6

The problem with using sandpaper to gain the clearance is that you are going to get microscopic particles of carbide embedded in the bearings.



I prefer just to have a machine shop turn the main journals down with a .0002" taper. My RX-8 e-shaft came with a .0001" taper out of the box.

sevenracer

What is the best way to get an accurate measurement of the rotor/main bearings and eshaft?



I tried a set of calipers and a set of micrometers on the eshaft - and I got about 1-2 thou difference with the two methods. Calipers consistently a larger number than the mics. I checked both using a 3" gauge block and both appear to be calibrated.



I bought a bore gauge to do the inside measurement of the bearings, and that thing is a real pain to use. what's a good technique to make sure you are at the widest part of the bore and square to the rotor? To me, it seemed to work best to move the gauge side to side to find the largest dimension for the diameter and then tilt the gauge up and down to find the minimum dimension - when the gauge is square to the bore. Seems like it would be easy to move a little laterally while tilting and affect the measurement.



Any advice on measurement techniques would be greatly appreciated.





Also, is it a valid measurement to clamp the rotor and a dial gauge to a table with an eshaft in place ( and leveled) then lift the eshaft from resting on the bottom of the bearing up to the top of the bearing and then note the delta on the dial gauge? Would that be an accurate measure of the clearance?



Thanks,

Neil