Atlas

Got a question.... what happens when you accidentally do a money shift in a rotary? Ie. Say ur gunning in 3rd, redline, then attempt to upshift to 4th but accidentally go into 2nd instead. Now in a piston engine you'd blow it but i was wondering - what happens in a rotary??? Do the rotors just spin insanely fast but then slow down??

Wing

First I'd say, how could you accidently do that? Second, It would probably be rather difficult to get it into gear.

rotory_it_up

My guess would be that the revs would start banging off the limiter like crazy. This would result in the rear tires locking up sending you into an uncontrollable spin!!! Or you could immediately push the clutch in and all would be good. Certainly some additional wear and tear on the drivetrain, but I don't think it would blow like a piston engine.

But that just my opinion...I could be wrong.

cueball

There is a rev limiter at 10k, so hopefully that would prevent any serious damage. Rotaries can take overrevving better than a piston engine, though.

Good Duck

The rev limiter will not protect the engine if the downshift exceed the engine design speed. Once the clutch is engage, the engine will spin up to the speed of the transmission. Unless the clutch is immediately disengage, damage will occur. Cutting the fuel, as the rev limiter do, will not help. Rotary engines are certainly more tolerant of over revving than piston engines, but to what extend, who know.

Sputnik

Exactly. A rev limiter cannot physically stop the engine from over revving. And it's not the fact that you are under power, it's the fact that the engine is spinning so fast.

When the new Toyota Celicas first came out, it was easy to put it in the wrong gear, and engines were occasionally overspun and destroyed on test drives.

---jps

rotory_it_up

Yep...I was wrong.

Quick_lude

This also happened to many of the new RSX-S 6 speed cars with "newbie" drivers. The gears were spaced closely together and they would mis-shift from 3rd to 2nd instead of 4th resulting in bent valves and a costly rebuild. This is a good question for us rotary newbs, what will happen if someone does this and revs the Renesis so say oh 14,000 rpm?

neit_jnf

I saw somewhere that the RENESIS was tested to be able to take 17,000 rpm without breaking, maybe I'm wrong...

Atlas

The rev limiter as previously stated doesn't help with over-revving because the wheels are already spinning at that speed. The rev limiter only cuts fuel on ur way up the rev range... once past not much it can do i guess.

Good Duck

Maybe so, but which one of you are willing to test that hypothesis?

SA22C

Imagine the inside of a rotary. The twin rotors are spining in their orbits around the eccentric shaft. As they spin past 10k, the eccentric shaft begins to flex. At an undetermined RPM, the eccentric shaft flexes enough for a rotor tip to make physical contact with the rotor housing. The contact gouges a crease into the housing, eliminating compression and breaking the apex seal, which proceeds to spin around the combusion chamber, wreaking yet more havok. At this point, the engine stops running. Upon teardown, the rotor housing probably looks like this:



Not a pretty picture.

red_base 95

Wouldn't the sychronizers in the tranny lock out 2nd above a certain speed? I believe there are dual cone synchros for 1st and 2nd gears. That would make it difficult for that kind of mistake - you would really have to force it into gear.

I do remember reading about the mis-shift issues on the new Celica and RSX, and there were some ugly results for owners. Do these cars have dual cone synchros for their trannies?

How about taking the shifter boot off, and manufacturing a gated boot - maybe out of aluminum or brushed stainless steel? That might be a solution, and if done correctly, would look great.

Atlas

Dunno, but a guy did it on his BMW e46.

neit_jnf

It has TRIPLE cone synchros for 1st, 2nd and 3rd gear... :D

wakeech

:D that'd be sick... noisey, but sick.

Quick_lude

Ouch.. so this basically means a full rebuild? Rotors, housing, seals, maybe the eccentric shaft?

zoom44

slightly off topic. is that what the rotor housing will look like say if a piece of spark plug breaks off into the engine? there is a second gen rx7 at my mechanics which had this happen.

SA22C

Yeah, it basically means a new engine. Of course, we don't know how far past 10k the Renesis will go. All we know is that the fuel cut is at 10k. I know that stock 12A's in the first gen RX-7's exhibt dangerous e-shaft flex at 8500 rpm plus. I would imagine that the Renesis is probably fairly safe into the 11.5k range, as Mazda competition motors with hardened gears and what not can go into the 10k range on a regular basis with heavier rotors than the Renesis.

I doubt it would be as bad as the pic I posted. If it got jammed between an apex seal and the housing wall, it could make a pretty mean gouge though. The Achillies heel of the rotary engine is the rotor housing. They are chromium plated, and when that plating begins to flake, the housing is basically scrapped. It's not like a cylinder that you can toss a sleeve into, unfortunately. I've always wondered why Mazda didn't just make a chromium plated sleeve for the rotor housings. It probably had to do with the exhaust port on the housing. Now that Mazda has moved to side ports, maybe it will be possible to re-chrome the rotor housings.

I'm rambling a bit now, but there was a guy on the rx7club.com forum that was investigating ceramic coatings for rotor housings. Here's the thread, it's still active, and the guy is making progress. If this works, it's the holy grail for rotary engine builders, as the most expensive part of rebuilding rotaries is replacing the rotor housings.

http://www.rx7club.com/forum/showthr...g&pagenumber=1