Subject: Center main bearing
From: ACRE
Date: 2/15/2005, 5:35 PM



         Thanks Jon.
     >
     >      I took the pictures at Hayes Rotary Engineering who were charged with overhauling
     >      a  CW RC2-60. It is the first  CW engine or picture or drawing of a CW RC2-60
     >      I ever saw with a center main bearing. I was under the impression that the
     >      CW RC2-60 never had a center main bearing. All the drawings I have are of the 2
     >      main bearing version. Here is an example.
     >
     >      The incentive for the center main bearing is the shaft is deflecting over
     >      10,000 RPM and the rotor tips are rubbing on the end housings. Some taper
     >      the rotors for this reason. Ken Welter among them. Road racers are again
     >      experimenting with center main bearings. I have recently seen at least
     >      one but I was sworn to secrecy.
     >
     >      I would be interested in seeing a drawing on the engines that have failed
     >      the center main. One obvious fact is the torsional stiffness and strength
     >      of the shaft would be reduced if the center main diameter was significantly
     >      less than the current size of the material connecting the two eccentrics.
     >      Perhaps the diameter or length of the failed center main bearing was not large
     >      enough due to an underestimation of the loads it would see.
     >
     >      Two or more row radial engines have similar problems with center main
     >      bearings and they typically have very large diameter roller bearings in
     >      this location.
     >
     >      Paul Lamar

     > Hi Paul,
     > I have no drawings of the Deere engines, but the center bearing design was nearly identical to what you have shown for the RC-60 engine. The bearing failures were ultimately attributed
     to a subtle
     > design problem with the oil feed to the crankshaft. Regarding shaft deflections, you can see in the cross-section of the RC2-60 engine that there was a so-called "outrigger" bearing (a
     rolling
     > element bearing) on the shaft close to the crankshaft pulley. By constraining the shaft at that end, the entire shaft will run straighter. I have an RC-2-60 engine that I "rescued" from
     the scrap
     > heap (I literally took it out of a dumpster!) when Deere decided to discard a warehouse full of historical engines and parts (a real shame, but another story....) I chose the particular
     engine I
     > have because it was a two bearing engine, and I didn't want to deal with the problems of the center main if I ever overhauled the engine. Most of the RC-2-60 engines did have center main
     bearings.
     > Jon

     I did not know that about the RC2-60. I thought they were all like the drawing.
     That engine will be worth alot some day.

     That is interesting. Scrapping historical stuff not only happens here in
     the US and Canada with the Avro Arrow but in England too. Sanders Roe built
     the equivalent of the Spruce Goose in aluminum. It wound up on the scrap heap
     as well.

Don't forget that the RC-60 series of engines was Curtiss-Wright's development "workhorse." There were many, many different things built into the engines over the years. Your drawing just represents
a single snapshot of development. The engine was run in single, twin, and four-rotor versions, with aluminum rotor housings, with cast iron rotor housings, with aluminum rotors, iron rotors, side
ports, peripheral ports, all kinds of spark plug configurations and locations, removable pocket rotors, thermal barrier coatings, carburetors, stratified charge direct injection, magneto ignition, a
zillion different apex seal and trochoid coating configurations, different oil seal configurations, side housing coatings... etc.
Jon


Wow. I had no idea. What was the goal if any?

Paul Lamar
 
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