Part 10 Flywheel Removal ...

Introduction ...

This page contains photos of the process of removing the flywheel from a ROTAX 912ULS engine (built August 2006.



ROTAX 912ULS magneto flywheel removal

Image 1

To remove the magneto flywheel we first need to lock the crankshaft. This is done by removing the crank locking screw blanking bolt and inserting the crank locking pin ...

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ROTAX 912ULS magneto flywheel removal

Image 2

This one doesn't appear to want to be removed without excessive force so we apply some MapGas heat to the head of the blanking bolt directly (NOT the crankcase). This component is supposed to be installed dry and with a copper gasket but occasionally I come across bolts that appear to have been installed with Loctite. The application of heat helps to free up any Loctite if it has been applied. Heat the blanking bolt and then allow it to cool down and try to undo it again. Having applied heat it should undo relatively easily now. Again a low torque applied for an extended period of time will turn the bolt without damaging the bolt head ...

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ROTAX 912ULS magneto flywheel removal

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View of the crankcase with the blanking bolt now removed ...

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ROTAX 912ULS magneto flywheel removal

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Next removing one plug from each cylinder makes rotating the crankshaft a whole lot easier ...

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ROTAX 912ULS magneto flywheel removal

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Next bolt some sort of bar to the propeller shaft flange to facilitate easier rotation of the crankshaft. We need to rotate the crankshaft until cylinder 1 is at TDC. Then and only then can the crankshaft locking bolt be tightened as it only tightens home when the crank is in this postition. There is a V section cutout in crankshaft that the locking pin locates into when fully screwed in. If you ever have cause to lock the crankshaft using the crank locking pin then ALWAYS ensure that the battery is either disconnected or isolated. Supplying power to the starter motor once the crank locking pin is in place will result in the crankshaft turning and the end of the crankshaft locking pin breaking off and sitting in the bottom of the crankcase - not a good outcome! ...

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ROTAX 912ULS magneto flywheel removal

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The cranking bar is just bolted to the propeller flange ...

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ROTAX 912ULS magneto flywheel removal

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Here we have found cylinder 1 TDC and we can now screw the crank locking pin into the crankshaft. There is a V section cutout in the crankshaft and the locking pin locates in this V cutout. By very gently rocking the crankshaft back and forward using our cranking bar at TDC we can ensure that the crank locking pin is fully tightened and thus seated right into the centre of the V cutout. This is very important. But don't overtighten ...

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ROTAX 912ULS magneto flywheel removal

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Once the crankshaft is safely locked we can put a socket on the flywheel bolt and undo it ...

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ROTAX 912ULS magneto flywheel removal

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Here we can see the crankshaft bolt partially undone ...

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ROTAX 912ULS magneto flywheel removal

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A view of the flywheel with the flywheel bolt removed ...

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ROTAX 912ULS magneto flywheel removal

Image 21

Note the cutout to accomodate the woodruff key which effectively locks the flywheel trigger timing ...

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ROTAX 912ULS magneto flywheel removal

Image 22

Rotax make two different flywheel pullers for the 912 - the short version and the long version. Either will do if you are working on the engine "on the bench". If you are working on a 912 in-situ in an aircraft quite commonly the short puller is the only one you will be able to use due to restriction of access e.g. there is not enough space between the rear of the engine and the firewall to use the long version. For a sprag clutch repair / replacement it is quite common to have to remove the engine from the airframe ...

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ROTAX 912ULS magneto flywheel removal

Image 24

Before using the flywheel puller we need to position a protection "mushroom" on the end of the crankshaft otherwise the large bolt of the puller will damage the thread on the end of the crankshaft. With the mushroom in place when we tighten up the puller the puller bolt will bear up against the mushroom ...

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ROTAX 912ULS magneto flywheel removal

Image 27

The protection mushroom on the bench. It can be a good idea to position the mushroom on the end of the crankshaft with a small amount of blue tack to ensure it stays in place when you screw the flywheel puller on and tighten it's bolt. If you dont do this it is possible for the mushroom to dislodge and then you could be tightening the puller bolt onto the mushroom without it being in the correct postion. Once the flywheel puller is screwed onto the flywheel you can no longer verify visually that the mushroom is in the correct position ...

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ROTAX 912ULS magneto flywheel removal

Image 26

Note the end of the bolt from the flywheel puller has been finished to be smooth. If you don't finish the end of the bolt like this the flywheel puller bolt can damage the protection mushroom itself so taking a moment to finish this bolt smoothly is time well spent ...

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ROTAX 912ULS magneto flywheel removal

Image 28

Having ensure the protection mushroom is securely in place screw the flywheel puller onto the thread on the flywheel ...

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ROTAX 912ULS magneto flywheel removal

Image 29

Next turn the flywheel puller bolt until the flywheel releases. Sometimes the flywheel just "lets go" gently. Sometimes they pop off the crankshaft with some vigour. Safeguard against the flywheel popping of and landing on the floor bu adequately supporting it! This impact can damage the flywheel magnets. Also note that using heat to release the flywheel can damage the flywheel magnets and the delicate coils immediately behind it on the stator so heat is best avoided ...

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ROTAX 912ULS magneto flywheel removal

Image 30

Here you can see the flywheel has released and is being eased gently off the crankshaft by continued rotation of the the flywheel puller bolt ...

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ROTAX 912ULS magneto flywheel removal

Image 31

The flywheel on the bench ...

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ROTAX 912ULS magneto flywheel removal

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Note the triggers ...

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ROTAX 912ULS magneto flywheel removal

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Note that there is evidence of rust on the inward facing magnetic poles. This is not anything to be unduly concerned about but once you have the flywheel off it's not a bad idea to clean this up a bit before re-fitting ...

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ROTAX 912ULS magneto flywheel removal

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Now that the flywheel has been removed we get a clear view of the stator ring assembly ...

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ROTAX 912ULS magneto flywheel removal

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Now the flywheel has been removed the crankshaft protection cap may now be removed ...

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