How often does a rotary engine need a rebuild?

[re5anovice]

I'm very up on when bikes like my GT750 Kettle or Triumph Trident need a fettle or a major go through, but what about the RE5? What sort of mileage sees major work needed, as a rule? What wears out when, basically?
I'm not holding anyone to it, just views roughly on lifespans of the major engine parts.
Thanks.

[re5anovice]

What wears out first?

[wayne]

I don't have direct experience stripping down and examining proper units but I'm helping you build up posts by a bit of back and forth.

From what I gather, there is very little wear on the apex seals but that's just part of the story.

I'm not sure there are many RE5's out there that have actually worn out. They usually die after being left to sit and end up with sticking seals.

There is a member on this board who has owned RE5's since new and has in excess of 150,000 miles on original proper units. I think he has one with 200,000 miles (!).

My own M has only 25,000 miles on it but the proper hasn't been touched in 44 years. It even sat in storage for nearly 20 years but was turned over regularly (and I think that's the key). It still develops 45 hp at the rear wheel (47-48 ish is ballpark for a new one) and has compression of 130 psi. Nothing wrong with that.

I also have an A which rides fine but is nowhere near the M in engine condition. It's a beautiful bike with only 5000 miles but sat for 30 years or more. It's compression is about 110 and HP about 40 ish from memory. Sitting in a shed for decades is just about the worst thing for them.

So, looked after and ridden regularly, they really last a long time. I would feel that if you bought one with a good engine or had one rebuilt as part of your restoration, you will not wear it out in your lifetime.


Simple things like oil and water seals outside of the proper unit will fail. The water pump bearing is a potential problem and will lead to premature seal wear (easily fixed). The metering oil pumps pretty much do not fail but the oil line check valve into the carby does and can lead to premature failure of the engine (the valve can be easily replaced and is an essential "check" item when commissioning an old RE5). Carbys need to be rebuilt during your resto but once you get the set up right they're good for years. Points on this bike carry very little current and will also last for years and years. Just keep the cam lobes lubed. Original air filters turn to powder very quickly and can get sucked through the system so high on the list for checking/replacing. B point vac valves on the later bikes (the plastic version of this valve) are a bit fragile and fail but you don't need the system to ride and enjoy the bike- worry about it later if at all. Starter clutch issues are common and can often be fixed, at least on a medium term basis, by changing to straight gear oils. CDI units can be rebuilt but are pretty reliable. There's good step by step info out there on how to do this. As an aside, when I bought mine in '80, the CDI had failed. I replaced it, bought a spare, carried it with the bike and 40 years later it's still going on the first one. Very warm and sometimes melted wires under your seat is not uncommon among old RE5's. Some have been traced to faulty ignition switches but most to rectifier problems. Once again, not hard to fix.

But the propers themselves are pretty robust given the aforementioned rules.

Hopefully we'll get some experts chime in here on actual engine wear.

[re5anovice]

Ok that's handy to know. Thanks.

[HGH 770N]

Nice summary Wayne.
My experience in rebuilding Proper units sarted in the 1980’s when my early “m” with only 3k on it cracked its chamber across the plug hole .
I’m not sure if it was to do with the early 10deg BTDC set up or over tightening spark plug as some theary say, or maybe its just the casting in some chambers had faults in them.
Othe units I have stripped to rebuild are units that have been stood without movement for some years and if stored in damp conditions,the exhaust port with the exposed rotor / apex seals will rust and seize and the alloy on side plates will oxidize badly and separate from the nickasil inlay .
Oil burning units I have noticed are worse in the early production regardless of mileage.
I have replaced Re ground or NOS Oil rings and rubber seals with some improvements.
Side seals become seized in with in correct oils.
I have seen well sooted burnt deposits on the side of rotor and seals that I would think is not ash free oil.
Compression certainly increases after a good run and adding oil in your tank is a good safe guard until you are certain your check valve is working correctly.
( draw a level line or sticky tape on you meeting oil tank and check it when you re fuel to check the oil level has gone down )