In our last issue we looked at some of the common problems
associated with Rotax engines when adapted to ultralight use.
In this issue will go through problems associated with each group of engines in the Rotax
The engines we will be taking a look at are
Now before going any further there is one thing that should be
mentioned about the Rotax line of engines, and that is that they, unlike many of their
competitors have a history, dating back many decades. The main overall advantage of this
to engine owners is that data is available on just how long that engine can be expected to
last, its weaknesses, and strengths.
First hand experience, over 35 years, on Bombardier snowmobiles engines and 17 years on
ultralights engines all types has shown me that the average RELIABLE life of a
Rotax engine points equipped aircraft engine is approximately 150 hours, with the life of
the new ducal CDI ignition engines being 300 hours, at which time if the engine is torn
down, and new rings, crankshaft, wrist pin bearings, wrist pin clips, seals, gaskets,
points, condensers, and spark plugs, and any other damaged or worn parts, are replaced
with new, then the engine will run for another 150/300 hours with a reasonable rate of
This is not to say the engine is going to self destruct at 150 hours I know lots of
engines that have gone on for many more hours, I also know of lots of over time engines
that when they did blow up, seize up or whatever, ending up costing the owner considerably
more to repair than if the engine had been rebuilt at 150/300 hours. (Remember if the
engine quits the possibility also exists that's damage can also be done to the aircraft in
an emergency landing).
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. Parts and
service for the 185, are available from Reg's Air Cooled Engines, 9708 Princess Drive
Surrey BC v3v 2t4, 6045817414.
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ROTAX 277 CC ENGINE
The 277 Rotax engine is probably the most trouble free engine, in
the Rotax family. Problems have been reported however with motor mounts, on such planes as
the Falcon, Skyseeker, and Challenger, and should be an area of regular inspection. These
mounts are similar in most cases to those used on the 185 cc Rotax and have been reported
to shear, careful preflight inspections recommended of this area by all pilots using
single cylinder Rotax engines.
Another problem that has occurred is in the use of a belt drive system with the 277. Early
model 277 engines used a plastic bearing liner to support the crankshaft bearings in the
crankcase. Overtightening of the belts on a belt reduction system can cause this plastic
liner to compress, allowing the bearing and crankshaft to move inside the crankcase
halves. This can permit the magneto to come in contact with the lighting coils and stator
plate, located on the mag end of the crankshaft. For the proper way to adjust a drive belt
system when used on the 277 cc Rotax engine contact the REDUCTION DRIVE MANUFACTURER, the
ultralight manufacturer, or write Ultralight Alerts Covering the World of Ultralight Aviation .
Another reported problem is in the exhaust system supplied by manufacturers of some
ultralight aircraft. The exhaust system supplied by Rotax is specially tuned, to provide
the best performance and reliability possible, some manufacturers in adapting this exhaust
system to their design have changed the tuning length of the exhaust to better fit the
cosmetics of their design.
An example of this is the early model Chinook aircraft in Canada. The manufacturer in
redesigning the exhaust to fit his design changed the tuning, and performance on the
engine to such an extent that in some cases only 65 % of the available thrust was
obtained. You should check to see whether your aircraft is equipped with this exhaust.
Another commonly reported problem is with the wrist pin bearings on the 277. These
bearings have been reported to wear out causing considerable damage to the engine when
they do. Rotax has recently introduced a new cageless wrist pin bearing to help eliminate
some of the problems in this area.
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Several ultralight pilots have reported prop damage, overheating,
and or rattling, on aircraft powered by the 377/447 Rotax engines. Upon closer inspection
it was found that the lower cylinder and or upper cylinder cowl housing had:
1. cracked causing a rattling noise to be heard when running the engine
2. broken off resulting in pieces flying into the prop in pusher configurations damaging
3. found their engines overheating due to lack of proper air flow over the cylinders. The
only solution available is to replace the fan shroud housing with a new one. There is
however a steel housing available which has proven to be stronger than the aluminum ones
used on most engines. The reason for the use of the lighter cowling was to help US
manufacturers in meeting the legal weight requirements.
Rotax has introduced a new engine cowling for use on the 377,447, and 503 engines which
directs more air to the magneto cylinder, making for a cooler running engine.
Several ultralight pilots have reported rough running engines, and or engine failure. Upon
closer examination it was found that the aluminum intake manifold, on the single
carburetor equipped 377/447/503 had cracked in the area of the bolts used to fasten it to
the cylinders or at the point where the outer half of the manifold joins to the inner half
on the 503. The cause of the problem, can be that when the Rotax engine is disassembled
and then reassembled a special alignment tool is required to properly align the cylinders
before torquing the heads. (Another commonly reported problem is in the improper torquing
of the head bolts.) The proper procedure is to first align the cylinders using the
alignment bar, torque the head bolts, (to the specifications found in your service manual)
replace the cylinder shroud cowlings, and then replace the exhaust and intake manifold.
Without first aligning the cylinders before torquing the heads, the cylinders do not line
up with the holes for the aluminum manifold. Thus when the manifold is tightened, because
the holes are off ever so slightly, the manifold cracks. This allows air to enter the
engine causing a lean mixture, overheating, and possible engine seizure. It is strongly
recommended that if you are removing the manifold, cylinders, or heads that you properly
align them before retightening to proper specifications.
Another reported problem in the intake and manifold area is with the gaskets used to seal
the area between the manifolds, engine cowlings and engine block assemblies. On the
377/447/503 engines little tabs are designed into the shroud housings to allow the engine
assembler to place the gaskets into them to help retain them during installation.
Because of the gaskets location in behind the cowling, they are very difficult to
position, in some instances (where a mechanic is unfamiliar with the Rotax engine) the
gaskets have been allowed to slip down, and thus are not sealing properly (never use
sealant on any of these gaskets). This leakage on the intake side, can lead to a lean fuel
mixture resulting in overheating and possible seizure, with an exhaust leak having the
potential to do the same.
If you are installing these gaskets make sure that they are installed properly using these
tab, and it is recommended that new gaskets be used on anything but a relatively new
Another commonly reported problem with the 377/447/503 engines is with the disintegration
of the bottom end crankshaft bearings. In nearly all cases the engines are installed on
aircraft such as the Eipper MX, Rotec Rally and Skyseeker where a driveshaft is used, or
on the Challenger where a drive belt system is used. Some manufactures have updates
available to help eliminate this problem.
The life of the crankshaft end bearings appears to be considerably shorter when used in
these types of drive systems. Again first hand experience has shown that very seldom are
the bearings destroyed to this extent when a Rotax gear drive is used. It has also been
our experience that the type of engine oil used can play and important role in extending
the life of the crankshaft bearings.
Some oils especially those recommending a 100 to 1 mixture (the factory recommendations
is a 50 to 1 mixture) have shortened the life of these bearings to less than 40 hours,
while the rest of the engine is still in relatively good shape. Synthetic oils have shown
to reduce carbon deposits in the engine, but my experience has been that they do not seem
to have the same lubrication qualities as mineral oils, when it comes to the crankshaft
bearings. As well synthetic oils do not appear to have the same lubrication qualities as a
good grade of mineral oil when it comes to storage.
On engines that have been stored over the winter, where synthetic oils were used, we have
reports of rust forming on the crankshaft and wrist pin bearings. (For more information
please contact ULTRALIGHT ALERTS Covering the World of Ultralight Aviation .)
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Another reported problem in the crankshaft area of the Rotax
engines was in early 447 models (prior to serial number 3624176), these engines have a
different balance factor than models after this number. If your 447 engine serial number
is below the above then the installation of an electric start is not recommended.
(I also know of 5 crankshaft failures on 503 engines and 4, on 532
engines, all involved failure of the crankshaft in the center boss area, all the 503
failures were on MX aircraft, with 3 of the 532s being on Tierra's with belt drives, and
electric starts and one on a Gyrocopter with no electric start, but with a gear drive.)
Owners of ultralights using the 503 Rotax engine have reported loss of power and or engine
seizure. Upon closer inspection it was found that the shroud webbing used to support the
fan had broken locking up the fan and stopping the engine. It is recommended that if you
have a 503 engine you check the webbing for abnormal wear or cracks. The only solution is
to replace the fan shroud housing with a new one.
Another area of reported breakage involved the fan tower in the area of the four retaining
bolts that bolt the housing onto to the crankcase halves. The casings have been reported
to fractured immediately around the four bolts, and is another area of recommended
periodic inspection. To inspect remove the recoil, and then the four allen head screws
which retain the tower to the crankcase halves.
Numerous ultralight pilots flying ultralight aircraft powered by the 503 Rotax engine have
reported over heating and/or engine failures caused by overheating. Upon closer
examination it was found that a pulley sheave located directly behind the fan had broken
causing improper belt tension and or belt failure. In some cases the belt had been severed
by the sheaves sharp edges. In other cases the failure was caused the the incorrect
placement of the belt adjustment shims. The proper location for excess shims is directly
in front of the fan, under the locking washer. Be careful the lock washer is positioned so
as not to cut into the shims. It has been reported that the 503 is able to run without
this sheave, as long as the fan (the area on the back of the fan that the fan belt rides
on) hasn't been damaged.
It is strongly recommended that ultralight pilots run CHT or EGT gauges. The proper
operating temperature for most Rotax engines is 300 to 400 degrees F on CHT and around
1,000 to 1,100 degrees EGT. (425degrees and 1,250 degrees respectively are very close to
Another problem reported in early model Rotax engines was in the magneto becoming loose on
the crankshaft. This apparently was caused by the factory installing Loctite on the
crankshaft where the magneto fits on, or if the key was not bottomed in the key way. This
loctite has a tendency to turn to powder when subjected to engine vibration, causing a
loose magneto which then, has the potential to destroy the keyway, magneto and crankshaft
end. It is recommended that Loctite not be applied between the magneto and crankshaft on
any of the Rotax engines.
Another reported problem with the 503 engine is in the breaking of the studs which are
used to align the cylinders, and torque the heads. It has been reported that these studs
have broken immediately above the bottom series of threads on the stud, or at the bottom
of the top series of threads. This then causes the head gasket to blow, with a resulting
loss of power, and possible engine seizure. This could possibly be caused by over
torquing, or vibration.
On the 503 engine a special spacing tool is used in there assembling of the engine
crankshaft bearings onto the crankshaft. This too ensures the proper spacing between the
two end bearings and the PTO end. This space is required in order for proper lubrication
to reach the last bearing.
Another reported problem experienced by owners having engines rebuilt by mechanics
unfamiliar with the Rotax engine is in the use of engine seals with single, rather than
double sealing lips , and with improper spacing rings on the back of the seal. If you
engine is being rebuilt make sure to stress the fact to the mechanic that only Rotax
supplied seals and gaskets be used.
Engines are a lot like people. If fed right, exercised right, and placed in a comfortable
environment they tend to perform well. The environment that your engine is placed in plays
an important role in the kind of performance it is capable of delivering to you. The Rotax
engine crankcase temperature must not reach 185 degrees F. If it does the engine may tend
to "hyper ventilate". Meaning the engine runs very erratic, does not pull full
rpm or runs on (four strokes) when shut off.
The airflow around your engine installation should be such that the airflow keeps the
temperature inside the engine cowling well below this temperature. With the recommended
area allowed for air to exit the cowling being 3 times that of the air access area.
Well that just about does it for problems associated with the air-cooled Rotax engines,
next issue we will cover the 532/582 Liquid cooled engine, and the Rotax gear box.
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