Jonesboro

I read a lot of posts about FD3 owners who have had to deal with "blown motors". Does anyone know if there is a "most common" part that breaks resulting in a blown motor and the reason why? I suppose another way to ask this question is: What "break/failure" is the most common cause for blown motors and what is the most common reason that leads to the "break/failure" occurring?

I bet that someone with extensive experience rebuilding rotary engines would have some valuable insights they could share with all of us.

afterburner

1.The idiotic enthusiat.

Running lean.

RX794

DETONATION!!! Caused by running too lean, or the ignition timing being wrong.

DK

iTrader: (5)

It's "FD3S" not "FD3" ... OK? "Eff-dee-three-ess" not "Eff-dee-threes" ... it's not the plural form. The chasis code is FD3S ... "FD" for short.

The apex seals blow because of detonation ... running lean ... it's the same concept. It's really easy to understand if you understand how the rotary works. Go to this page and see the animation to see what I'm talking about: http://www.howstuffworks.com/rotary-engine3.htm

The apex seals on the pinnacles of the rotors serve basically as piston rings to seal to rotary combustion chamber. If you look at the cycle in the animation in the link above, imagine what would happen if detonation occured -- which is premature combustion due to hot and lean conditions (inter-related usually). If detonation occurs, the explosive power has no where to go. It wants to go out, but the rotation is still compressing and on the top side of the cycle, not on the exhaust port side of the cycle. So what happens? The energy usually is too much for the apex seals to handle and the fail.

Jonesboro

Well excussssse me! I didn't mean to offend anyone by using the term FD3 instead of FD3S. I promise to never use FD3 again, it was totally unthoughtful of me. I sure hope that I am not declared public enemy number two immediately following Osama. Can you get the death penalty for this offense?

Does anyone else notice that people on this Forum seem to have very short fuses and will jump on others and turn things personal at the slightest misstep? I don't mind be corrected, but keep the condescending attitude to yourself!

Back to the subject of this thread. Okay, detonation due to running lean. But since the ECU controls the air/fuel ratio, the cars aren't running lean due to improper operator adjustment like can happen in carburated engines. Is the lean condition occurring as a result of modifications that increase the engine's "ability the breath" beyond which the ECU can adjust back to a rich condition? Do you think this accounts for the majority of blown engines?

Is there also some other significant cause? From the posts I've read, I had the feeling that many of the reported blown engines had not been modified. For example, I've read any number of car for sale ads stating "engine replaced by Mazda", implying that the engine was replaced under warranty, i.e. the engine blew in stock form. Maybe I'm just confused about this scenario.

JConn2299

The other weak spot on the 3rd Generation RX-7 is the coolant seals.
They seem prone to warping and allowing coolant into the combustion chamber. I'm never been quite clear on why it happens. Is it general wear and tear, or is there some amount of overheating going on that causes this?

It seems that some people who have kept up on maintenance and not over-modified their cars have had this happen. If you're one of them,
maybe you can clue us in. Did anyone tear down your blown engine and explain WHY the seal went?

Mahjik

iTrader: (1)

JConn2299,

My coolant seals were gone when I got mine. The car was stock (at least when I got it) except for a RB Type I Wing and a RB Front Lip.

The mechanic just guessed at overheating but I know he really didn't know for sure. I don't know if the previous owner modified the car and then put it back to stock before he got rid of it, or if it was just not taken care of. It had about 43k miles on it at the time, so I'm leaning more towards improper care.

DK

iTrader: (5)

Jonesboro, chill on the rap, dood! What makes you think I had an attitude or was being condescending with my remarks about the chasis code? I agree that a lot of people here try to be internet tough guys or are short-fused, but not everyone is like that. You made a common mistake and I corrected it. I correct it a lot, so don't feel bad. I usually mention that it's a common misnomer by Americans, but people should know what their car is called. In Japan you'd be hard pressed to look in a catalog on not find it listed as "FD3S" over "91.11~ Mazda RX-7." I didn't mention that it's a common mistake not to be too ashamed of this time ... my bad. I didn't call you a "******* idiot" or anything like that, though, or have some angry faces or condesceding faces so you shouldn't have read into it. I should've had a smiley face or something. But see, I did explain how apex seals fail, didn't I? If I was being mean to you I wouldn't have bothered.

Running lean is pretty easy to do. Boost spikes cause it, cold days, partially clogged injectors, clogged fuel filter (stock is a Miata filter), and the things people do to cause things like boost spikes without considering the ECU, which can only compensate to an extent. There is an inherent problem in the setup of the FD's fuel delivery system that hampers the ECU -- it's based on a MAP sensor instead of a MAF sensor, which is much more ideal for turbo cars. A MAP sensor takes the air reading at the intake manifold, whereas a MAF sensor (which you can easily see on Nissans) is right behind the intake filter. A MAF sensor gives a computer more time to react to sudden changes in airflow coming into the motor (such as a boost spike or sudden WOT) and change the fuel delivery. A MAP sensor basically takes the reading too late, so the computer is actually guessing what fuel to send based on previous readings. See how that can cause a sudden lean condition? A boost spike is usually detected too late. There's very little you can safely get away with using a stock ECU. Beyond an intake, catback, and downpipe, anything else that affects air/air density entering or exiting the motor will need an ECU upgrade to remain safe.

Devilish

My engine died from a blown o-ring. Why? I still had the 1.3 radiator cap. Too much pressure on the cooling system. Now it's a .9 cap. Along with a Fluidyne radiator and the CWR dual oil coolers.

BlackR1

carbon build up

mine died because of clogged injectors/fuel filter

widebody2

Is there any way to know if your injectors are beginning to get clogged? or if they are getting worn? I have a bunch of mods and am pretty much broke now so I can't upgrade my injectors for now. Is there anything I could be monitoring to know whats going on with them?

ivanuscg

My seals just went after a long road trip from FL to NJ. Dave at KD told me was the Mazda didn't use very good water seals in the original 93=95 motors. Now they use better seals. A stronger material. Dave uses a silicon seal in his rebuilds. If that is what you want. They are supposed to be stronger and more heat resistant. What happens when the seals go, is that the coolant system becomes overpressurized because of the coolant leaking into the housings. This is not verbatum from Dave, but I'm just trying to get the point across. My add coolant lite would come on every few days or so after the seals started to go. I would add coolant to the resevoir and it would just pour outta the over flow. Because the system couldn't handle more coolant because it was over pressurized with air or gases from the motor. Thats what I got from him at least. The way I understood it. I'd have to wait a little while and add coolant directly to the water pump. Or else I'd be way to low. The car will have a very hard time starting when the coolant gets into the housings. Until the coolant is cleared from the housing it'll backfire and have a horrible idle. It fouls the plugs.

JConn2299

"My seals just went after a long road trip from FL to NJ. Dave at KD told me was the Mazda didn't use very good water seals in the original 93=95 motors. Now they use better seals. A stronger material. Dave uses a silicon seal in his rebuilds."

Ivanuscg,

That makes a lot of sense. It's the best explanation I've heard. Too bad we can't upgrade the seals WITHOUT doing an engine rebuild.

JConn