Mazda RX8 Engine Rebuild project

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.

Mazda RX8 engine rebuild project

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.

Mazda RX8 rebuilding project

In the context of Mazda RX8 flooding and hard-starting issues, it’s important to know how critical plugs, ignition wires, ignition coils, battery and starter are for reliable starting. These components should be in A1 condition-always, and this especially holds  true for high mileage 8’s. In fact, this is a universal rule for all Mazda Rotary vehicles.

Mazda RX8 engine rebuild project

I have completed the Mazda RX8 engine rebuild and about ready to add-on peripheral components; manifolds etc. To summarize, I’ve replaced all seals and Rotor Housings, flow-port the intake and exhaust, blueprint and added all the little tricks iI know to achieve maximum compression pressure. RX8 engines are not exactly easy to R&R because the engine sits down and back making transmission bolts all but inaccessible. I think the makers want you to remove engine and transmission as a unit from below the car. I did neither.


Mazda RX8 engine overhaul project

OLYMPUS DIGITAL CAMERA While assembling the Mazda RX8 engine I noticed a blue tag on the front cover that I did not see before could it be that this is not the original engine; the tag and numbers on the Rotor Housings suggest that this motor is not the original and was most likely changed by Mazda. There is no information on the engine history of this vehicle so I’m assuming that this is probably the second installed by Mazda. So this not an old worn-out engine after all and it makes the hard start-flooding issue even more interesting because hard-start issues are usually from high mileage engines.

Mazda RX8 engine rebuild project

I’ve now completed the reassembly of the Mazda RX8 motor which originally had the low-compression/flooding issues. I was really surprised to see the small amount of wear on the Rotor Housings. The apex seals were measurably worn with no chamfering or distortion. Side seals had the large clearance which seem to more on earlier 8’s. I am still pondering how the compression could have drastically dropped on the old engine (causing?) it to hard-start and flood. It almost doesn’t make sense; the typical RX8 scenario is one day the engine refuses to start and spins over freely (low compression) like an electric motor. Unless some extreme measure is taken such as pouring a light oil directly into the engine, it might remain in that mode indefinitely. After struggling to restart it suddenly catches and if allowed to run and warm-up is back to normal again-really weird. I am taking a second look at old rotor housings which have areas of dark brown deposits suggesting the engine apex seals were not scraping against the Rotor Housing surface. (See picture) I was able to remove the stuff in sheets with a razor blade. Over the years the old bugaboo about Rotaries and synthetic oils is the lubricant’s tendency not to burn-off completely in the combustion process and leaving deposit-build up on the Rotor Housing surface. I have seen this many times over my long career building rotaries but could never tell if synthetics were responsible.OLYMPUS DIGITAL CAMERA

Mazda RX8 rebuild project

Mazda RX8 engine rebuild. After thoroughly inspecting all internal engine parts, I started the rebuild process with new rotor housings and seals. New side seals were carefully carefully cut to obtain minimum clearance. For those attempting this special care has to be taken because an improper cut could ruin the seal, or it might  jam when engine is assembled. I am taking every measure to get maximum compression sealing in this engine (blueprinting) since the original issue was compression loss and flooding. To maximize engine breathing capability I flow-ported all intake and exhaust ports. Flow-porting maximizes intake and exhaust gas aerodynamic flow through the engine, resulting in horsepower gain, more smoothness, better drivability and small improvements in fuel economy (See pictures).

Flow-ported RX8 intake and exhaust ports

Flow-ported RX8 intake and exhaust ports