Rotax 185 cc ultralight aircraft engine

The 185 cc Rotax engine was primarily used on a craft manufactured in Canada called the Lazair. Two engines were mounted, on this ultralight, one on each wing.
To date some 25 owners have reported that they have had crankshaft failure on their planes using this engine. Some in as little as 75 hours. Most with over 200 hours. This apparently is caused by the use of a direct drive prop on the engine, which puts a severe load on the crankshaft, both from vibration and from the load exerted by the prop during the change of flight attitudes.

Another reported problem is with the studs, and nuts used to fasten the carburetor, to the cylinder. These studs have been reported to vibrate out of the cylinder allowing the Tillitson carburetor to fall off. Also the nuts have been reported to loosen permitting the carb to become disengaged from the cylinder. It is suggested that if you're using the 185 cc Rotax on your ultralight that you apply BLUE LOCKTITE on the studs and safety wire the nuts. (CAUTION: We also have reports of the bolts shearing off, at the drilled hole, when holes are drilled to allow placement of safety wire).

Another reported problem is in the recoil used on the 185. On early Lazairs the recoil was mounted solid, while the engine was allowed to move. This causes the recoil cup located on the magneto to come in contact with the inside of the recoil mechanism. This caused wear on the two parts, and generally resulted in filings entering the magneto, resulting in loss of spark, and possible ignition damage. The factory solution for this problem was to switch to a Tecumseh small engine recoil mounted to the ENGINE.

Another area of concern is the engine mounting system. In most applications the engine is mounted on rubber motor mounts, which have a threaded rod coming from each end. These mounts have been known to SEVER, and the engine to become disengaged from the aircraft. Other styles of mounts have suffered the same sort of failure, which would indicate that the vibration generated by the 185 cc engine, tends to wreck havoc on motor mounts.

Pilots have also reported difficulty in finding air filters for the 185cc Rotax engine. An air cleaner that is available for the Tillitson carb, and is readily available is used on Chrysler West Bend Marine engines, and some gas powered lawn trimmers. (Check to make sure the element isn't paper or synthetic material).

Another commonly reported problem in the adaptation of the 185 engine to ultralight use is with the exhaust system. On most Rotax powered ultralights an exhaust canister, with a flex pipe extension coming off the canister and going to the cylinder head is used. This flex pipe has been reported to fail in several places. Also failure of the canister itself has been reported where the flex pipe joins in at the top of the muffler.

The 185 engine is equipped with a decompressor button to aid in starting, this button has been known to seize open possibly causing overheating and or seizure.

Another reported problem is with parts availability for the 185cc Rotax engine.

Lazair Ultralight. Factory Lazair pilots let it all hang out at Sun-N-Fun 1984.