Rebuilding  the Rotax  377 ultralight aircraft engines.

This manual has been prepared as a guide to help service and repair the 377, 447, and 503 Rotax air cooled ultralight engines. It is primarily published to be used with the "Rebuilding the Rotax ultralight engine video," produced by Ultralight Aircraft News. Some of the terms used in the manual and in the video may not match those used in parts manuals available for these engines. All pictures, diagrams, drawings or graphs, used are for the general identification only, and are not to be taken to represent technical drawings or replicas of exact parts.

When rebuilding a Bombardier Rotax ultralight engine is strongly recommended that the rebuilder use only original manufacturers replacement parts.

WARNING !

This information relates to the service and repair of Bombardier Rotax ultralight engines, and has been used safely and effectively. However I Disclaim liability for any and all damages and or injuries resulting from the improper use of the contents. It is strongly recommended that any service to be carried out be verified by a highly skilled, knowledgeable ultralight engine mechanic.

Introduction

This manual covers the following Bombardier Rotax ultralight engines.

Type Rotax 377 fan cooled ultralight
Type Rotax 447 fan cooled ultralight
Type Rotax 503 fan cooled ultralight

To verify engine type consult serial number plate located on fan shroud housing.

Engine lower shroud removal

Tools required

Racket
13 mm socket
10 mm socket
6 mm allen wrench
plastic or rubber mallet

Rotax engine lower engine shroud removal

To remove the bottom shroud (2 on the 503) using the () mm allen wrench remove 4 bolts retaining the exhaust manifold. With the 13 mm socket remove the 4 bolts holding the intake manifold. With the 10 mm socket remove the self tapping screw from the PTO side cylinder cowling on the 503. With the rubber mallet gently tap intake manifold to break it free if necessary. With the manifolds off remove the lower shroud(s).

CAUTION !

It may be necessary to GENTLY TAP the intake manifold with a rubber mallet to free it from the intake manifold gaskets, as the tend to stick to the lower cowling.

Inspection:

Inspect the intake manifold for cracking at the retaining bolt holes, and for leakage at the gasket, or sealing ring between the two intake manifold halves.
Inspect rubber intake socket for signs of UV deterioration.

Rotax fan tower removal

Tools required

() mm allen wrench
() mm socket
ratchet

Locate the 4 ()mm head allen bolts retaining the fan tower to the crankcase halves. Remove them and the fan tower will come free. At this time it is suggested the two ignition wires running to the coils, blue on red/blue on black, the ignition suppressor box wires and the engine ground wire (brown) be disconnected. To do this remove the three ()mm self threading bolts holding the lower coil to the fan tower. This will allow disconnection of the ground wires. The fan tower can now be removed completely from the engine.

Inspection:

Inspect the fan tower in the area where the four allen bolts retain it to the crankcase halves for cracking.
Inspect the fan tower in the area where the fan supports attach to the fan tower.
Inspect the fan for cracks or sign or damage.

CAUTION!

ENGINE IS EXTREMELY HEAVY AND AWKWARD. DO NOT ATTEMPT TO REMOVE FROM AIRCRAFT WITHOUT ADEQUATE HELP!

Rotax engine top shroud removal

Tools required

Ratchet
13 mm socket
flat screw driver
10 mm socket (for 503)
Plastic or rubber mallet

To remove the engine top shroud, remove the three 13 mm socket head bolts located on the top of the engine cowling. (4 bolts on 503) Loosen the 6 (8 on the 503) slotted screws located at the seam of the upper and lower shroud halves. The top shroud should now lift off.

Inspection:

Inspect the top shroud for cracking, missing pieces.

Rotax fan cover removal

Tools required

Flat screw driver

To remove the fan cover, carefully pluck the three retaining clips from the holes holding them into the fan tower. Then gently pull outward on the cover, until it is off.

Rotax aircraft engine rebuilding manual for the 377, 447, and 503 aircraft engines.

Recoil removal

Tools required

extension ratchet
10 mm socket

To remove the recoil from the engine remove the 4, 10 mm socket head bolts that retain it to the fan tower. Disconnect suppressor box, remove recoil.

Inspection:

Inspect the recoil housing for cracking around the center, and where the recoil rope exits the housing.
Inspect the recoil rope for fraying.

Starter Pulley/Fan Pulley and Fan Belt Removal

Tools required

( ) allen wrench
locking pin
plastic mallet

Located behind the recoil starter assembly is the starter pulley and fan pulley. To remove these lock the crankshaft, by placing the locking pin part # (), into the fuel pump impulse hole. The slowing turn the engine over until it locks. With the crankshaft locked use the () allen wrench to remove the 3 ()mm bolts. This allows the removal of the recoil cup and pulley. It may be necessary to gently tap the fan pulley with a plastic or rubber mallet.

Caution !

Note the direction of travel of the fan belt prior to removal by locating the writing on the belt and noting the direction.

Once the cup and pulley have been removed rotate the fan belt in the fan blades until it is off.

Inspection:

Inspect the starter pulley cup for signs of wear or damage.
Inspect the fan pulley for signs of wear or damage.

CAUTION!

This is a special locking pin developed for this purpose. The use of any other tool, or material may cause serious damage to your engine.

CAUTION !

During removal of the magneto, the key used to align the magneto to the crankshaft may come loose, and can be easily lost. When pulling the magneto free be careful not to loose the key, or that it does not get pulled into the magneto.

Caution !

Make sure that the puller bolts are the correct length. The use of incorrect bolts can strip the magneto threads and/or damage the internal coils.

Marking the stator plate
Tools required
Hammer
Chisel

To aid in reassembly it is suggested that the stator plate and crankcase be marked at this time. To do this take a chisel, and hammer and imprint the stator unit and crankcase half with an alignment mark.

Stator plate removal

Tools required

() mm allen wrench

Remove the two () mm allen screws, washers, and lock washers holding the stator plate to the crankcase halves. The stator unit will now come free. Slowly pull the stator plate out while pulling the wiring harness through the crankcase hole. Once the wires are free the stator unit can be completely removed from the engine.

Inspection:

Inspect the stator unit for signs of wear or damage.
Inspect the points and condensers for signs of oil contamination.
Inspect the coils for damage.
Inspect the wiring for wear, cuts, or pinching.

Caution !

Be careful not to cut or bare the wires on the sharp edges while pulling them through the crankcase hole.Removing the cylinders

Tools required

Rubber mallet

Removing the cylinders

With the cylinder heads removed the cylinders can be GENTLY lifted off. It may be necessary to tap the cylinders gently with a rubber mallet to break the cylinder base gasket free.

Inspection:

Inspect the interior of the cylinder for signs of wear or damage.
Inspect the interior of the cylinder for signs of seizure.
Inspect the interior of the cylinder for signs of aluminum deposits.
Inspect the cylinder with your finger about 5/8s of an inch from the top for signs of wear.

CAUTION !

During cylinder removal ensure that the pistons and connecting rods do not bang against the side of the crankcase halves or head studs. Be EXTREMELY careful that damage is not done to the piston/ skirts during removal of the second cylinder.

Removing the wrist pin clips

Tools required

Ice pick or other sharp pointed tool
Rag or paper towel
Eye protection

For disassembly it is only necessary to remove two wrist pin clips. These are the clips on the PTO side and Magneto side of the pistons. While wearing eye protection, carefully insert the point of your tool into the groove on the side of the wrist pin hole, until it is under the wrist pin clip. Using a rag or a towel with your other hand cover the clip area. Now slowly apply pressure and pry the clip out.

CAUTION:

The wrist pin clip is very springy, use a rag or other material to prevent it from flying free. Wear eye protection. Clear work area of bystanders.

Wrist pin removal:

Tools required

Wrist pin puller/socket/screw driver
small hammer

To remove the wrist pin raise the magneto piston to TDC. Insert the wrist pin puller through the pin, lock the puller clip tighten up the puller to extract the pin.

To remove the wrist pin with a screw driver or socket, use a socket or screw driver that is a slight smaller diameter than the pin. Come in from the side of the pin that still has the wrist pin clip in it, Gently tap the top of the socket until the pin is free.

Once the pin is free remove the piston. To prevent damage to the piston never place the piston on its skirt, always lay it on its dome.

Repeat the procedure for the piston on the PTO side.

Rebuilding  the Rotax  377, 447, and 503 ultralight aircraft engines.

Inspection

Inspect the dome of the piston for signs of damage.
Inspect the dome for signs of carbon build up, and ignition burning pattern.
Inspect the rings for signs of damage.
Inspect the piston sides for signs of seizure.
Inspect the rings for signs of seizure and carbon buildup.
Inspect the ring dowels for signs of damage or wear.
Inspect the ring lands for signs of damage/wear/carbon build up.
Inspect the wrist pin clip retaining groove for signs of wear damage.
Inspect the piston sides for signs of wear or damage.
Inspect the base of the skirts for shine, indicating piston slop.
Inspect the underside of the piston dome for carbon build up.
Inspect the wrist pin bearing for signs of wear or contamination.
Inspect the wrist pin for signs of bluing ( an indication of heat), wear, or damage.

CAUTION:

Always lay the piston on its dome! Support and protect the piston and connecting rod assembly to prevent accidental damage.

WARNING: If your engine is equipped with cageless wrist pin bearings these bearings will fall out once the wrist pin is removed. Take whatever steps necessary to prevent their loss Separating crankcase halves.

Tools required

Ratchet
10 mm socket
13 mm socket
() mm allen wrench
Screw driver
Rubber mallet

Separating the crankcase halves

To separate the crankcase halves, turn the remaining engine assembly upside down, so that it is sitting on the cylinder head studs. Remove the 4, 10 mm head bolts (on the 377/447) from the outside of the cases. Remove the remaining 13 mm head bolts, from the casing, starting from the one end and working to the other.

On the 503 some of these 13 mm bolts at the PTO end of the casing have been changed to allen head bolts to allow for socket installation.

On the 503 the 4 outside bolts are 13 mm head rather than 10 mm.

With all of the bolts removed, insert a screw driver into the non sealing area between the crankcase halves and pry up gently in several places on both sides of the casing.

Then using a rubber mallet gently tap the crankshaft at either end to break it free from the casings. The bottom crankcase should now come free. After the bottom case has been removed, remove the crankshaft, by placing your hands around the crank at either end and using your thumbs pry down on the casing while lifting up on the crank until it comes free.