Rotary Resurrection - Tech Section
Internal Engine Damage:
Rotary engines usually wind up having one of 3 major defects that cause them to stop running properly. I’ve documented a few examples here so you have an idea what the problem inside your engine may be, and what to plan for during the rebuild.
Apex Seal Damage :
Most of the time, rotary engines die due to blown apex seals. Usually, what happens is that one seal cracks/breaks, but it doesn’t stop there. This seal often shatters at speed (while the engine is running), and fragments fly around inside the rotating engine, taking out everything in their path, including the next 2 apex seals, the rotor, and it’s rotor housing. Effectively, this means half of the engine is no good, and is not rebuildable. This is why new/used rotors and housings are required to rebuild a blown rotary. IT is possible, but unusual, to have only one seal crack, but remain intact and do no damage to anything else, however this is VERY rare. Here are some pics of damage common to blown apex seals.
Coolant Seal Damage:
The second most common failure of rotaries is bad coolant seals (water seals). Basically, this is the equivalent of a blown headgasket in a piston engine, leaking combustion gases into the cooling system, and coolant into the combustion chamber. This condition runs closely with overheating. Sometimes, some failure will cause the engine to overheat, and thereby kill the coolant seals. Other times, the seals themselves fail due to age or a bad coolant jacket (on the iron plate) and cause subsequent overheating from coolant loss. Either way, the result is the same, an engine in need of a rebuild. Often these engines are fully rebuildable, or at least almost so, as overheating does not damage rotors and very seldom rotor housings.

Often when this condition occurs owners simply shut the car down and leave it for months at a time, until they can afford repairs. This is the worst thing you can do for the engine (provided that you’d like to rebuild it in the future, or that it could be of some core value to a rebuilder). Water pools up inside the engine and causes the rotors and irons to rust. While an engine is compressed (assembled), all spring loaded seals are almost flush with the surface of the rotor, and normally when you disassemble an engine these will be pushed back out of the rotor by the spring. However when theyre allowed to sit in water (such as a bad coolant seal motor, or one you throw out in your back yard or a humid area uncovered), they become useless, as the seals in the rotors rust up and are impossible to get out without damaging the rotor. The rust also destroys the iron plates, and only the rotor housings (sometimes) are useable…sometimes rust actually penetrates the chrome coating inside the housings and causes it to flake off, making them useless as well. Below are some pictures of coolant seal/overheating/rust damage. Note that if you preserve the engine with oil of some sort (injected soon after the engine is retired, to displace water and rust) you won’t have to worry about the rust issue.
  The cause/result of bad coolant seals in most cases, a ruptured water jacket, allowing combustion pressure to force the seal and gases into the coolant passage, and letting water drain back into the engine once it is shut down. This cannot be reliably repaired, and the iron(s) afflicted must be replaced:
Carbon Buildup and Carbon Lock
You hear a lot of talk about carbon buildup in rotaries. There are many potential causes, the general consensus is that lack of redlining the engine, and poor oilchange habits (since crankcase oil gets injected and burned via the OMP) are the worst contributors. Over time, the carbon builds up and can cause seals to stick. Its even possible for a chunk to fall off and cause a seal to break. Removing the OMP system and running premix can help combat carbon buildup and keep the internals clean and moving freely. Also, regular treatments of water injection can help steam clean the internals (there is a writeup elsewhere in the tech section about this).

Sometimes you hear people talk about carbon lock in a rotary. This is said to be when carbon jams itself in a corner of the engine and prevents it from turning…most of the time people refer to this when they have a engine that seized during shutdown or startup (cranking, slow rotation). IN reality, carbon lock in a rotary is very rare. The only time, in disassembling at least a few hundred cores, that Ive seen true carbon lock was on my personal FD when I bought it. There was literally 1/8” thickness of carbon on the face of each rotor, and it finally got so thick that it contacted the rotorhousing walls and could no longer spin. These are not pics of that engine, but they show a fair amount of carbon buildup on a neglected (low mileage) engine.
Rotary Resurrection - Tech Section
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