Causes of Rotary engine failure

[NoDOHC]

I would make this a poll, but I would be sure to miss some common failure mode, so I will not do so.

Here is what I have found:

Gradual Loss of compression:

Caused by:
Chrome Flaking (Primarily effecting 12As, pre-'86 13Bs) - Also seen some on S4s.
Corner seal chipping -housing wears to allow corner seal to overextend, it get crooked and ruins side plate (Typically seen on S4 NAs, although I just found an S5 with the initial stages of it).

Oil Seal Failure:

Caused By:
Dirty oil
Overrevving when cold
Age

Naturally aspirated:

S4 engines lose coolant seals:
Caused by:
Improper antifreeze
Housing corrosion (improper antifreeze or old age)
Age of seals (brittle)
Overheating
housing material composition/porosity issues

S5 engines lose coolant seals:
Caused by:
Overheating
Age of seals (brittle)
(I have not seen the other failure modes for an S5)

Engine seizes:
Caused by:
Running out of oil (I have never seen this one, but it must exist)
Oil pickup tube coming off
Sitting too long and having carbon buildup jam an apex seal, preventing the engine from rotating
Carbon buildup in intake ports (especially the 6PI of the front rotor) coming loose and jamming in the combustion chamber as the rotor passes TDC
Massive apex seal failure
OMP failure and no premix (never seen, but must exist)
Fasteners dropped down the intake

Apex Seal Failure:
Caused by:
Excessive wear (especially on the pre-'86 13Bs and 12As @ > 200,000 miles)
Carbon buildup breaking loose as a chunk and going through the engine
Carbon buildup on spark plug catches apex seal and nicks the center, starting a scoring pattern on the housing
Fasteners dropped down the intake
Excessive Nitrous Oxide use

Turbo (this is where my experience is much more limited):
S4 coolant seal failure:
(same as NA)
S5 coolant seal failure:
(same as NA)

Engine seizes:
Running out of oil
Oil pickup tube falling off

Apex seal failure:
Most common cause is stock ECU cutting fuel to rear rotor during an overboost condition. Frequently caused by exhaust upgrades or lack of exhaust maintenance.
Detonation under boost (Carbon buildup decreases detonation resistance over time)
Lean detonation due to fuel starvation (plugged filter or empty tank)
Pre-ignition caused by improper tuning/ECU spark timing errors.

Side seal failure:
Improper Porting techniques/Improper Port size
Severe overheating
Carbon Buildup

Turbo failure:
Oil Seals (fills intercooler with oil sludge, smokes really bad, can kill engine with carbon lock)
Bearings (usually on a modified car (FCD, etc.))
Exhaust turbine (Never seen, but must exist)
compressor wheel:
Corrosion/pitting
fasteners going through the turbo
Nut coming loose (only heard of once, on rebuilt turbo)

The purpose of this thread is to build a list of common failures to help those who have not yet had them to avoid them.

If you have maintenance procedures that avoid these failures, please include them too.

Thanks for the excellent input so far!

Please continue to contribute, I think this would be a service to the rotary community.

This list may become a mess, suggestions for better sorting are also welcome (Generation Specific / Failure with generation description / etc.).

[NoDOHC]

I will start:

I have personally disassembled 3 NA rotary engines that were seized or had bad seals due to carbon buildup in the 6 PI sleeve of the front rotor coming loose.

To fix this, I always take the upper and lower intake manifold off any rotary engine that I get when I first get it and clean everything up, remove any carbon buildup from the sleeves, remove buildup from the intake manifold.

I change or clean my spark plugs frequently because I have seen several rotary engines with the telltale ring around the inside of the rotor housing.

[Whizbang]

i have experienced most failures from either wear or high oil comsumption leading to carboned up engines

[PercentSevenC]

Originally Posted by NoDOHC

Engine seizes:
I have never seen or heard of a 4-port seizing

I have. Specifically, it was a 12A, but it could happen with any engine. Turned out the oil pickup tube was not properly installed and had actually fallen off into the pan. The e-shaft was basically welded to the rotor bearings as I remember, and there were some nice burn marks on the irons. Freaking Hayes.

Originally Posted by NoDOHC

Apex Seal Failure:
Caused by:
Excessive wear (never seen, but must exist)

I've heard of very high-mileage engines, especially '84+ 13Bs, where the apex seals got worn down so low that they basically "rolled" out of the rotors.

Here's another mode of failure: severe corrosion in the water jacket. In one engine we tore down (in fact, it was the 12A that was in my FB when I first got it), there was corrosion into the spark plug holes in the rotor housings, allowing coolant to enter the combustion chamber. I've also seen some that had corrosion that extended into the coolant seal area. This tends to happen if the engine is run with straight water.

[12arotary]

I've never had a "locked up" 12a to where it wouldn't rotate, in my experience if an apex in one breaks for any reason its usually small enough to just shatter and keep going-
and the high millage roll out exists on the 12a too, I had an 83 with 241k on it, all of a sudden I lost about 1/3 the power- when I removed the exhaust there was a bent apex in the corner of the stock mani- upon breakdown the other two seals were fine just that one came strait out


Add Carbon flake to any 13b or 12a NA pre-85 I've lost many engines just simply with too low compression to keep running do to large splotches where the housing just flaked off ESPECIALLY 12a's with over 150,000 miles

and to the s5- i've lost a coolant seal simply from old age, never over heated never abused just went

you might also add hot spots in the s4 na category- i've seen poor coolant flow that warped the housing its self around the spark plug area causing poor compression or total apex break

[NoDOHC]

Awesome!

I will update the list.

I really appreciate FB guys stepping up, as I have no experience with 12As or pre-'86 13Bs

[Whizbang]

my 1987 turbo II died from the oil seal in teh turbo being crapped and thus causing a massive amount of oil consumption leading to carbon breaking an apex seal!

[TitaniumTT]

Side seal failure - overheating........ severly. Seal must have expanded into the corner seals with all the heat, had nowhere to go and just shattered. This was a fresh engine, about 1000 miles with TIGHT clearances set.

Side seal failure to carbon lock - basically the same thing as the overheating

Coolant seal failure - Using Dex-cool or Redline Water wetter. There is a chemical in those two that EATS away at coolant seals.

Lets not forget to add things like
misfires cause pre-ignition. Haltech vehemantly denies this but how many rotary owners have lost engines on the highway when barely in boost only to find in thier data-logs a 50* BTC fire? Talk to Joe about this

Improper tuning - again, too much ignition lead, not enough fuel, whatever the case may be turbocharged rotaries die early deaths at the hands of thier tuners daily.

My favorite one that is just so hard to prove though is using parts during a rebuild that really shouldn't be reused. E-shafts for example, how man people bust out the V-blocks and dial indicators and mic the bitch up? I firmly believe that alot of people pull these things out and don't mic every last little piece, they just say, it came from a running engine, it'll be fine. When it blows, it destroys the piece that was in question so the answer become a mystery that perpetuates the myth that rotary engines are unreliable.......... this coming from the guy that has gone through 4.5 engines this year. But let me tell you my story

Engine #1 - purchased as an import sometime around 2003. Sat in someones basment until 2004 when someone else bought it to let it sit in thier garage until 2005 when I bought it. It sat in my garage until 2006 when I started my swap which took 2 years - 5 years just sitting. It had REW housing so I knew it was rebilt. She made 105psi comp so I said what the hell and ran her for ~5 hours before I lost the carbon locked side seal and chuncked 1/2 the engine.

Engine #2 - I rebuilt and clearanced everything to the best of my abilities. Broke her in for ~800 miles, she put down 313RWHP on WG and 36 hours later was run to ~265* oil and water temps during an emmisions test - lost a side seal

Engine #3 - made 346 RWHP before she ran out of fuel on the dyno @ 4800 rpms on the 1st pull and went to 13.6 AFR's, warped two apex seals.

Engine #4 - Didn't even dyno this one, found a sticking corner seal on the comp test. Here's what I'm talking about. This rotor really shouldn't have been reused but it was matches and cryo'ed and I really didn't want to wait so I worked that corner seal with some compound until it was free'er that when it was when I started. It still wasn't as free as the others. When I broke it down I spent HOURS working that seal and recess until the seal moved like glass.

Engine #4.5 - still running awesome, dyno'ing in T-Mius 84 hours