Hello all,

This is my second technical question as a new member. I took some time looking through older posts and threads, but did not find this topic. As indicated in my introduction, I am collecting new parts to build a 13B for my 1990 N/A RX-7 convertible. The one new part that I want to add is an eccentric shaft for this series of motor. I have checked around the internet, and apparently this part is no longer available new. However, the eccentric shaft for the 93-95 FD 13B engines are still available. Could I use this e-shaft outright, or will it require dynamic balancing with my new rotors? This motor is not going to be used for racing, and therefore it definitely won't see anything above 6,500 rpm. I'm also still looking for a front counterweight for the 89-91 13B as well.

 

An FD shaft will be fine, it has a taper pre-machined into the rear main journal per MFR and comp spec. The RX8 will also work as it has the same taper, and it's lighter - though I've seen them bend a bit easier granted at sustained 9k road racing conditions.

 

welcome to the board.

you can use the FD shaft in any 13B. balancing is not necessary.

actually, your S5 car is good to use any S5 and newer front counterweight, but it has to be Rx-7, not Rx-8.

in general, the S5 internal engine parts (the rotating assembly) are basically the same as the FD. however, the oil pump is totally different. the front stack parts are slightly different as well, but can be retrofitted.

https://mazdatrix.com/rotor-weight-a...ression-chart/

 

Thank you for your prompt response. This advice is especially encouraging because I can now go ahead and acquire a new FD front counterweight while they are still available.