Part 29 Re-Fitting The Cylinder Heads ...

Introduction ...

This page contains photos of the process of re-fitting the cylinder heads to a ROTAX 912ULS engine (built August 2006).



ROTAX 912ULS re-fitting the cylinder heads

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So our starting point is that all cylinder barrels have been refitted and are lightly secured in place temporarily by the reassembled cylinder heads. The cylinder heads now need to be removed one by one and the pushrod tubes (previously removed for cleaning) need to be rebonded to the cylinder heads using a sparing coat of Loctite 648. Apologies ... I omitted to take photos of this step. The piston for the cylinder you are currently refitting needs to be positioned at TDC so that neither valve is opened / compressed and new pushrod o-ring grease and then placed on the end of the pushrod tube that fits in the crankcase. Then the cylinder head can be refitted ...

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ROTAX 912ULS re-fitting the cylinder heads

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Before that we need to remove the old pushrod o-rings from the crankcase ...

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ROTAX 912ULS re-fitting the cylinder heads

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With a small pick gently prise the existing o-ring out of the crankcase ...

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ROTAX 912ULS re-fitting the cylinder heads

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Clean out the grooves they locate into in readiness for the new o-rings ...

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ROTAX 912ULS re-fitting the cylinder heads

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Here a set of new o-rings "on the bench". Place these on the crankcase end of the pushrod tubes with some GP grease, Then gently slide the cylinder heads back onto the cylinder studs being careful to locate the crankcase end of the pushrod tubes correctly. ...

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ROTAX 912ULS re-fitting the cylinder heads

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Do this for two cylinders on one side of the engine e.g. cylinders 1 + 3 or cylinders 2 + 4. Once they are loosely located in place attached the Rotax cylinder alignment tool to the bolt holes on top of the inlet manifold. This tool ensures that the cylinder spacing is correct when you come to torque up the cylinder head nuts. An inlet manifold assembly can be used for a similiar purpose however this tools is smaller and easier to handle (and it is the tool of choice specified in the Rotax Heavy Maintenance Manual) ...

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ROTAX 912ULS re-fitting the cylinder heads

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The cylinder head collar cap nuts may now be torqued up progressively using the pattern described in the Heavy Maintenance Manual up to the target static torque after which a rotation torque is applied. See the Rotax Heavy Maintenance Manual for the exact procedure that must be followed ...

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ROTAX 912ULS re-fitting the cylinder heads

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The rocker covers may now be re-fttied ensure that you use a new centre o-ring and a new o-ring for sealing the outer edge of the rocker cover ensuring that the o-ring sits in the retainer pinches in the rocker cover. A little GP grease is useful here to ensure that the outer o-ring does not stray from it's designated position whilst you torque up the rocker cover ...

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ROTAX 912ULS re-fitting the cylinder heads

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Be careful to observe the 0.2 mm recommended gap between adjacent rocker covers that allows for expansion between the cylinders. Failing to observe this gap can cause barrel distortion at operating temperatures ...

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ROTAX 912ULS re-fitting the cylinder heads

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Once the cylinder head collar caps nuts have been torqued up the cylinder alignment tool may be removed ...

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ROTAX 912ULS re-fitting the cylinder heads

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Note that now the inlet manifold on the cylinder heads are now open and vulnerable to F.O.D. When you have finished this side of the engine it makes sense to plug these holes with an uncontaminated rag ...

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