Rotax 377, Rotax 447, Rotax 503 proper cylinder alignment required
during reassembly.
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Ultralight aircraft safety advisory
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Aircraft:
All ultralight aircraft using the 377, 447, or 503 Rotax engines.
Incident report:
Several ultralight pilots have reported rough running engine, and or engine failure. Upon
closer examination it was found that the aluminum intake manifold, had cracked at the
bolts used to fasten it to the cylinders.
Suggestions:
The cause of the problem, is that when the Rotax engine (377,447,503) is disassembled and
then reassembled a special alignment tool is needed to properly align the cylinders before
torquing the heads. If the cylinders are not properly aligned then the holes used to mount
the intake and exhaust manifold are off ever so slightly.
The proper procedure is to first align the cylinders using the alignment bar, torque the
head bolts, replace the fan 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, then 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 and overheating. It is strongly
recommended that if you are removing the manifold, cylinders, or heads that you properly
align them before retightening to proper specifications. |
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Rotax aircraft engine cylinder alignment bar. |
Damaged intake manifold repaired after
cylinders were not aligned during engine rebuild. |
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