Mazda Rotary Engine RX cars have been sold in the U.S. since the early seventies and have had a significant number of die-hard followers. There is something very special and almost addicting about Rotaries. Maybe that’s from their design which gives them the uniqueness of being the only production car with a non-piston rotating gas engine with exceptional power and smoothness. Mazda discontinued it’s only production Rotary-Engine car exported to this country (RX7) in 1994 but ten years later (2004) brought the Rotary back in the form of the RX8. I am constantly reminded of the Rotary’s allure when I see so many young people who are knowledgeable and enthusiastic about the used Mazda RX7 or 8 that they own or are about to buy. I will discuss what to look-out for when buying an RX7, RX8, or even older models in my upcoming blogs.
With the rebuild behind me, i’ve slowly begun the breaking-in process. I highly recommend long breaking-in for freshly built rotaries; 600 mi. to about 3000 mi. From my experience the longer the break-in the better the engine will run. Technically, after about 600 miles the rebuild is “broken-in” but experience has taught me that it’s at around the three thousand mile mark where the engine really comes alive. The project car is not intended for me to drive daily. It will be up for sale shortly. My advice to anyone purchasing a used RX8 is to first find out engine history; how many miles are on the engine. Of course one has to assess the body also.
So with this Mazda RX8 engine rebuild completed what did learn about the original hard-start, flooding and accompanying low compression issue?
First, looking strictly at the evidence I found areas on the rotor housings where it appears that the apex seals were not making contact, the apex seals were worn, and the side seal clearances were a bit excessive. Everything else inside the engine appeared to be normal. In my opinion the rotor housings showed reasonable wear and were reusable. Side seals and all seal springs were ok. So what are the conditions or mechanisms responsible to throw the engine into a no-go mode? The answer is not an easy one, but I believe that the new shallow apex seal grooves found only on RX8 rotors coupled with the “short” apex seals might be responsible. Could a situation develop where after x amount of miles on these engines the apex seal springs fatigue and with wear on the already short apexes they get stuck in the grooves? The missed contact patches (see earlier blog pics.) attest to this. Carbon flaking from the rotor’s combustion pockets may be the agent that wedges the apex seals in their grooves. As I mentioned this is a difficult problem to diagnose because it does not mean that all RX8 rotor housings will have patches of no-contact on them. Based on what I’ve found in this project engine those are my conclusions. I have more ideas that I will blog later.