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Rotax engine service - aircraft effected: All ultralight aircraft.
Incident report:
(1) An ultralight pilot has an engine seizure on his craft. After getting the craft
down safely he removes the engine and takes it to a local mechanic who works on small
engines, and snowmobiles.
The mechanic indicates that a piston has seized and removes the
cylinders, hones them, flushes the engine out, replaces the damaged piston with a new one
and reassembles the engine. The pilot replaces the engine onto the aircraft does a couple
of hops and then takes off. 10 minutes into the flight the engine seizes up again.
(2) An ultralight pilot has an engine that is running very erratic, he takes the engine
to a local small engine mechanic. The mechanic takes the engine, apart, and finds that one
of the end bearings on the crankshaft has started to disintegrate. The plastic liner that
holds the ball bearings in place has all but disappeared.
The mechanic indicates to the
owner that the bearing should be replaced with a bearing which uses a steel liner, since
the steel in much stronger and will not wear out as fast as the plastic. The owner agrees
and the mechanic rebuilds the engine using the new bearings with the steel liners.
The owner puts the engine back on his craft, does a couple of test hops and then flies
for another 20 hours before the engine seizes up once more.
(3) An ultralight pilot has a rough running engine he takes it to a small engine
mechanic. The mechanic takes the engine apart, reports to the owner that the engine is
badly worn in the crankcase bearing retaining area, and that several of the crankshaft
bearings are badly worn, as is the crankcase.
He replaces the bearings with new bearings
using a steel liner rather than the original manufacturers parts which use a plastic
liner. In addition he removes but does not replace 5 rubber plugs, found in the upper
crankcase half. To repair the apparent wear in the crankcases he uses a substance that
when it hardens is suppose stop the bearing from further wear.
He then reassembles the engine, replacing points and condensers. The owner then
reinstalls the engine on the craft, and does several circuits. The engine will not develop
proper RPM. Suspecting the newly purchased ground adjustable prop he calls the dealer that
has sold him the prop.
The dealer drops buy checks the prop for proper pitch, the pitch is
correct, the dealer has brought along a prop from another aircraft that is powered by the
same size engine. He installs it but finds that the engine will still not develop full
power. He puts a finer pitch on the prop, and the engine starts to develop full RPM.
Unable to explain to himself why the prop will run fine on one aircraft, and not the other
the dealer leaves.
A week later the dealer gets a call from the ultralight owner. The engine was running
fine, developing full RPM right up until the time that it seized up. The dealer asks the
owner whether seizure is evident on the side of the pistons. The owner replies that the
pistons are fine but that it appears something has seized up on the crankshaft.
The dealer
who is quite knowledgeable on Rotax ultralight engines, schedules a day to go over and
look at the engine. Upon arrival he is warmly greeted after his 5 1/2 hour drive. He
proceeds to tear down the engine. After pulling off the magneto he notices that stuck in
the magneto magnets are a nut and lockwasher used to retain the point wires to the
condenser, both nuts are still on the condensers.
After removal of the cylinders he prepares to remove the wrist pin clips, but is unable
to do so because the last installer has placed the clip in such a position that the
opening in the clip is located at the indent for clip removal. Thus there is no way of
prying the clip out. After nearly an hour he is able to extract two clips and removes the
pistons.
He also notes that the pistons have been modified by the last mechanic. Grooves
have been installed in the piston directly below the rings. The purpose explains the owner
was to provide better lubrication. The bottom rings however are seized. After removal of
the crankshaft he notices that the two end bearings have seized up on the crankshaft. A
major contributing factor to the seizure was that the material used to REPAIR the
crankshaft had worked its way into the drip holes used lubricate the bearings blocking off
oil from entering the bearings. As well material had entered the bearings causing bearing
damage.
(4)An ultralight pilot has his engine tuned up by a local snowmobile dealer. The dealer
replaces points and condensers and resets the timing. The owner reinstalls the engine.
Flies for several hours only to have the craft develop a peculiar miss at high RPM. An
ultralight dealer on mobile service work in his area drops buy, after hearing about his
problem from another pilot.
He does several checks and finds that he is not getting a
proper reading from one set of points. The owner and dealer remove the engine from the
aircraft and the pull off the magneto. The problem appears to be quite evident. The nuts
and washers holding the points wires on to the condensers are both loose.
Upon further
examination it is also found that the wire running to the points has been rubbing up
against the crankshaft, and is worn through, and is now grounding out on the crankshaft.
After replacing the points (which come with a new wire) with a new set of points and
resetting the timing the engine once again runs correctly.
Suggestions:
In all of the cases above the problem was not with the engines involved. It was with
the owner of the craft taking his engine to someone who isn't involved in the ultralight
industry, and doesn't have enough ULTRALIGHT AIRCRAFT ENGINE REBUILDING KNOWLEDGE to
properly rebuild an ultralight engine. There are differences in an ultralight engine and a
snowmobile engine. In the first example the engine seizure was originally caused by a worn
crankshaft seal, causing a lean mixture, had the mechanic completely disassembled the
engine rather than just doing the top end he would have found the real cause of the
seizure and fixed it.
In the second example the mechanic in question suggested the replacement of the
bearings with what he considered to be a stronger bearing. While it might be true that
steel is stronger that plastic, there is a reason that steel bearing liners are not used
in Rotax ultralight engines. WEAR ABILIYTY, Simply put the plastic liner, will slowly
disintegrate, if improper fuel and lubrication are used, or the time between rebuilds is
too great.
This causes an engine over a period of time to slowly loose power, run erratic, or
misfire. The pilot might not become aware of this right aware, but over a period of time
he will notice it. If he checks his spark plugs regularly he might notice a different burn
from one plug to another. He might find that the spark plug gap on one plug keeps closing
down, (from material from the plastic liner hitting the electrode). Note the pilot however
in most cases in still on the ground, looking for the problem. Over many decades of engine
rebuilding I have very seldom seen an engine seize up because of the plastic liner
deterioration. On the other hand I probably get two or three calls a month from
disgruntled pilots after these same bearings have been replaced with bearings with steel
liners and the engine has seized in FLIGHT, and the pilot is not looking for the problem
but for a place to land.
In the other case remember that your average snowmobile dealer in most cases is not
equipped with either the tools or knowledge to properly set up an ultralight engine. Most
of the engines currently used on snowmobiles are equipped with CDI ignition, and even that
is totally different to the CDIs that were are using.
Another problem is with the type of thinking involved. Where you might be able to
repair something on a snowmobile that is used to tow a fish hut out on to the ice once or
twice a year, you can not use that type of work ethic when it involves the lives of
individuals flying aircraft. When that snowmobile engine quits, the person simply walks to
shore, or hitches a ride with the next machine along the trail. When an engine quits on an
ultralight, on takeoff, the next ride could be in an ambulance.
Remember the saying don't open your doors to strangers!
One last point, while ultralight dealers may not be able to sell you spark plugs, fuel
filters, fuel line, spark plug wires, caps, gasket sets, etc. as cheap as your local
Canadian Tire, hardware store, snowmobile dealer, or motorcycle store, because he can't
buy in the volume quantities, he none the less needs your support to survive.
It takes nearly 5 years to develop an ultralight business, (after
30 years I should
know) to the point where it can stand on its own. During that time that dealer will
probably have lost thousands and thousands of dollars, while investing many 80 and 90 hour
weeks trying to make ends meet. Each dollar you spend with him may help get him over that
hill, that at times seems like a mountain.
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