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Rebuilding the Rotax 377 ultralight aircraft engine. |
Inspection
With all the engine parts clean and dry, it is time for a reassembly inspection. Before
putting the engine back together any worn or damaged parts must be repaired or replaced.
This requires physically inspecting and/or measuring the various engine components.
Inspection
.-Inspect the piston for signs of wear or damage. Look for signs of damage to the dome.
This could be an indication that foreign material has entered the engine, or that internal
engine parts have entered the combustion chamber.
Inspect the bottom of the piston skirts. A shiny ring around the base of the piston skirt
may indicate that the cylinder bore is out of round, or enlarged .
Inspect the ring seating areas, they should be free of carbon deposits and should not be
damaged. The rings once installed should move freely on the piston.
- Inspect the dowels used to position the rings, for damage, and make sure that they are
not loose.
-Inspect the underside of the piston dome for carbon build up, and clean if necessary.\..
Inspect piston dome Refer to Section I tolerances, for pistons, cylinder, etc.
Inspection
.-Inspect the wrist pin bearing for wear, signs of foreign material, and or overheating.
-Inspect the wrist pin for damage, wear, and overheating.
-Inspect the connecting rod ends for signs of heat and wear.
-Inspect the cylinder head, for signs of damage. -Check the cylinder head for
warpage.
-Inspect the crankcase halves for damage. Look carefully at the bearing seating areas. If
a bearing has spun in the case it maybe necessary to repair or replace the crankcase
halves.
-Inspect the crankshaft bearings for wear, free play, and or contamination's.
-Inspect the crankshaft key way for signs of wear.
-Inspect the points, condensers, and internal wiring, for signs or wear, rubbing, or oil
contamination. Loose fitting condensers, oil on the points, or between the condensers and
stator plate, may cause erratic engine performance ..
-Inspect the magneto for foreign material, cracking, and wear on the keyway.
-Inspect rotary valve shaft for wear, in area of seal location.
-Ensure rotary valve shaft is straight.
-Inspect rotary valve gear, shim and bearings, replace is damaged.
Note
It is recommended that all 377 engines equipped with cage style bearings be updated to
cageless bearings.
Warning
It is necessary to replace or modify pistons to use new bearings.
Measurements.
..To ensure that the engine parts are not worn past the point of repair it is necessary to
measure the affected components.
Measuring the cylinders
After the cylinders have been cleaned, all aluminium deposits removed, and the cylinders
honed, measure the cylinder at two locations. The first across the top of the cylinder 5/8
of an inch from of the cylinder lip. Measurement north to south, then east to west.
Then measure the cylinder just above the intake ports, again measuring across east to west
and north to south.
Compare these measurements with the wear limits.
Measuring ring end gap
heat cylinder and rings to 68/70 Degrees F. Using the bottom of the piston install a ring
in the cylinder just above intake port. With a feeler gauge measure the gap between the
ring ends. Repeat 5/8 of an inch from the top lip of the cylinder.
Measure ring end gap just above intake ports
Compare these limits with specifications.
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