Removing the magneto on McCullcoh Mac Cat 839 chainsaw. I need to get this off to enable me to get at the oil pump seals. The chain lubricant just pours out, so I need to get the magneto off to strip the pump down. Any ideas? As the thing keeps dam well revolving I don't want to damage the fins.

Tony Bennett, October 2007

The flywheel is held on by a nut, but its also on a tapered, keyed, shaft. Remove the nut (which may be left or right hand thread) gently (very gently) prise the flywheel with 2 screwdrivers, put the nut until the threads are covered and give the shaft a tap with a hammer, but don't overdo it! Normally we use a proper extractor for this but my method should work if you're careful. To stop the flywheel rotating I use an air gun to shock the nut off but a lever through the fins may work - but they are easily fractured.

John, December 2007