OT: Mazda RX7 FC3S

[Mux213]

Okay, some small words about RX7s and reliability.

First off all, especially from the FC model onwards (1986+) these cars were very well build. They had great anti rust coating and such and they really only rust when damaged (jacking damaged on the sills, or accident damage), though even after 20 years the best cars can get surface rust in places.
Anyways, its easy to pick up a car thats in a great shape exteriorly.

Engine wise is a different story. Rotary engine's have a bad rap reliability wise. In part this is for good reason, in part this is shit. A few facts:
1) my car has 200.000 miles on the odo and the engine was still pulling strong when I started taking her appart
2) Mazda scored high and even won a few times during the LeMans endurance races with rotary engines. You don't win LeMans if your engine isn't relyable
3) There are alot of people in the states that adapt the 13b for use in home build small aircraft. You don't want unreliable engines in aircraft.

So why the unrelyable reputation? Very simple. The rotary design has a simple design fault (or limitation really). Your standard otto design has a crackshaft driving your pistons, these things go up and down. The crackshaft is nicely position above a big pool of oil and this oil is spray all over the place nicely lubricating the crankshaft, the rods, the pistons, and it even gets as far as lubricating the piston seals.
Now we all know that you shouldn't drive a piston car fast when the engine is still cold because the oil is still thick and can't get everywhere, but there is adduquate lubrication from the start.

With a rotary engine the story is different. With the rotary engine the rotors turn 8 shaped circles (sorry for the poor description) within the chaimber constantly creating intake, combustion and exhaust areas that create power. Lubrication works by pumping oil around and spraying it on the excentric shaft and such. There is one place the oil can't get and thats to the (apex) seals on the sides of the rotors that close of the intake/combustion/exhaust chaimbers.

Mazda solved this by injecting (dripping is a better word) tiny amounts of oil into the combustion chaimber to lubricate these seals (ps one of the reasons people think rotaries use oil, first, rotaries do consume tiny bits of oil, but second, when this system brakes it can be that it is set to full drip, and it can go through a liter of oil over 100km )

There are a couple of things wrong with this approach:
1) on a cold engine, there is no oil, there is no lubrication. It takes a little while for the system to get going. Rotary engines wear extra fast when cold
2) they are injecting engine oil into the combustion chaimber. Oil is not meant for this purpose and may react differently depending on their additives. Some oils work fine, some oils will become sticky when burned (or leave sticky residue), some oils simply don't work to well. One of the reason Mazda even to this day for the RX8, tells people to use mineral oil without additives.
3) if the dripping system brakes (OMP pump), and it often does, no more lubrication, bye bye engine
4) the longer you drive, the more dirty your oil gets, the more dirty your oil gets, the dirtier the junk you drip into your engine. Not only does it clog up the drippers (see point 3), but think what it does to the apex seals...

Its not uncommon to take an engine appart after 150.000km and find out the rotors are black with gunk and the apexes are fixed into place by all the dirt thats gone into the grove.

Anyways, needless to say, its this system that if you don't take proper care of your rotary, causes increased engine wear. Mazda recommend oil changes every 3000 to 5000 kilometers (half to 1/4th a piston car), if you don't stick to that, your engine will die early.
Also for some reason turbo's rotaries wear extra fast. I always thought the boost cause extra stresses on the apexes (often its the breaking of apex seals that causes a turbo engine to fail, take engine apart, replace apex seals, put back together, go) but I'm not sure nowadays.
N/A rotaries when taken care of last and last and last and last, just as long as a 4AG.

There is a solution to the above btw that many owners use. Mazda used it on their leMans cars. Those guys that use the rotaries on their aircraft use it.
Solution is simple really. Use an oil ment for the job, the stuff you put into your moped. Yups, good old 2 stroke engine oil does wonders for rotaries. Just through some in your gas tank every time you fill her up, and she keeps on going.
The lemans cars, the aircraft, and many rotary fans actually alter the OMP to not take oil from the engine oil reserviour but from a separate canaster filed with 2 tact oil so they don't have to keep throwing the stuff into their fuel tank.

Again, I've seen engines pulled apart after 150k, or 200k, but then completely clean. I even heard about a story from a guy with a 3rotor cosmo that blue an apex (bad apex) and they had to pull his engine appart after 60k and the guy doing so told him he thought the engine looked like it was put together just yesterday.

Anyways, stuff works amazing. And yes, when treated right, rotaries can be relyable.