Project FD RX7 Restomod: Part 19 – Assembling the 13B REW

Now we were ready for the eccentric shaft.  Top we see a stock e-shaft and below is our WPC Treated and CTP Cryogenically Treated e-shaft.

Heat Treating the E-Shaft

As it turns out, Mazda induction hardens the surface of the e-shaft and does not heat treat down into the core.  Back in the day, Abel heat treated the e-shafts on his world-record setting rotary engines to make them stronger at high boost and high RPM.  This deep penetrating heat treatment dimensionally changed the e-shaft and sometimes affected its straightness.

This required the e-shaft to be straightened and the rotor and stationary journals ground back to the original diameters after heat treating.  The dimensions grew due to the transition from the brittle austenite grain structure to martensite, which is a larger and stronger crystalline grain structure of steel.

Cryogenically Treating the E-Shaft

The CTP Cryogenic process is also a form of heat treatment that changes the crystalline grain structure from austenite to martensite by bringing temperatures down to -300*F for hours.  In high quality, heat-treated billet steels, like high-end racing crankshafts, cams, and rods; cryogenic treatment does not dimensionally change the components.

The Mazda e-shaft is not made from a super high-quality steel and is only induction hardened.  Because of this, just like Abel’s heat treating, we also saw slight dimensional changes after cryogenically treating our e-shaft.  In our case, the e-shaft did not warp and the rotor journals did not change.  Only the stationary journals grew in size and had to be ground back to the factory spec between 1.6878” to 1.6917” in diameter.

It’s important to be aware of the potential need of machine work to grind the e-shaft journals back into spec after cryogenically treating it.  If you are not pushing the envelope of power and RPM in a 2-rotor, then you can skip this step and WPC treat the shaft with no side-effects.  If you want the strongest and most reliable internals, especially for a 3 and 4 rotor engine that deals with far more whipping motions and stress, then cryo treating the e-shaft and grinding it back to spec is probably a good idea.

The WPC treated e-shaft (right) has a distinctive matte silver finish as a byproduct of the process.  We talked about the benefits of WPC treatment in Part 12, and how the process bombards metal with a special media at high velocities that in addition to shot-peening like grain refinement via cold working.  There’s also a melting and quenching phenomena at a micro level that leaves a hard, micro dimpled surface that retains oil molecules to further reduce friction in addition to refining the surface grain structure of the metal, which greatly improves durability and reduces crack propagation and failures.

We’ve had a lot of success WPC treating crankshafts in piston engines, and the same friction reduction and strengthening benefits should be seen on the rotary e-shaft as well.  We installed the Mazda Competition .200 Eccentric Shaft Oil Jets into the e-shaft for improved oil flow and cooling.

We inserted the e-shaft into the rotor and stationary gear journals, paying careful attention to not force anything or cause nicks to the bearing surface.