Engine Decarboning: Pulling the Engine

WARNING: The author of this page is not a professional or certified aircraft engine mechanic. The information contained herein constitutes a description of the writer's experience only and should not be construed or interpreted by the reader as instructions or guidance for the successful completion of any repair or maintenance procedure. Use of any information contained herein is at the user's own risk. This information has not been reviewed, evaluated, or approved by the manufacturer of this engine.

First step is to remove the prop and disconnect all the engine's plumbing. The pulse pump is unbolted from its bracket and the pulse line is disconnected from the nipple at the crankcase. Then the carb boot clamps are released and the entire pulse pump/carb/fuel line assembly can be removed as a unit and hung from the aileron by a couple of long wire ties. The wire harness from the mag and ignition modules are disconnected as well as the positive lead to the starter. On the other side of the engine EGT sensors are pulled from the manifold and the exhaust system is removed as a unit. The plugs are pulled. The engine ground lead and all the sensors are hung from the starboard aileron. I decided to leave the redrive in place to minimize the time for dis and reassembly.

After positioning the engine platform under the engine, push down on the tail to take the weight of the engine off of the mounting bolts. The bolts are removed and the plane pushed forward. Plug and tape all the openings on the engine and it's off to the workbench. Total time for engine removal, 40 minutes. I know of owners who have done the decarbon job with the engine on the plane. If you've lowered the formers under the engine, or if the area under the engine is not decked over, you can remove the cylinders on the plane. This would have at least one advantage in that it would minimize the possibility of dropping anything into the case. But after doing the job this way, I don't think I'd do it any other way myself. Working on the bench is so much more comfortable, especially if it's cold.

Here's the engine on the bench. It's strapped to a pallet made to fit the cooling shround and support the engine without putting pressure on the plugs or anything else the projects from the shroud. The pallet also stabilizes the engine for transportation. A frame of 2" steel tube has been bolted to the engine mount. This frame provides a means of securing the engine to the bench when it's turned right side up as well as supporting and keeping the weight of the engine off of the ignition modules and anything else when its turned on it's side for piston removal.

The engine is secured to the bench heads up with the redrive hanging over the edge of the bench. The 2" tube frame is screwed to the workbench surface.. The cooling shrouds and intake manifolds have been removed and set aside. The cylinder head nuts are being loosened a little bit at a time in the same pattern used to torque them at installation and retorque. Four of these nuts are long. They're the ones that take the shroud and exhaust bracket bolts; make a note of their position for reassembly.When all eight nuts are off, the heads can be removed from the cylinders. There are washers under each of the cylinder bolts... be ready to catch em when you flip the head over to take a look.

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