Today I was finally able to begin disassembly of my exhaust system to investigte the damage done to my engine mount.  The right side cyl. tubes are too close to the lower tube of the engine mount and have rubbed a hole in the lower engine mount tube.



As can be seen in the photo, there is very little clearance between the right side exhaust tubes and the engine mount.  The brown scale appears to be burnt paint rather than rust.


Here you can see the hole where the front tube has rubbed and the place where the rear tube was also rubbing against the mount.


I spoke with Roger and Travis about this issue while I was at the Open Hangar day in Mexico, MO.  The explanation I was given was this relates to a running change made to the 912 series engines about 2005.  Rotax changed the starter so as to provide more torque.  The new starter was larger than original and had interferance issues with the CH-701 bed style engine mount.  Zenith changed the bed mount and exhaust slightly to accomodate the new starter size.


The problem I have is, my engine and exhaust are from a 2001-2003 vintage kit.  They would have fit the older style bed mount with adaquate clearance.  With the newer style mount, however, the older style exhaust can is now too close to the bed mount tubing.  Unfortunately, the jig for the older style mount is long gone.


I am in the process of removing my engine and  mount to weld up the damaged tube as per AC-43-13.  I am going to send Travis these pictures and we will hopefully be able to come up with some kind of tweak which will restore adaquate clearance between the exhaust and mount.  I have a couple of ideas but want to get Travis' feedback before sharing.


Doug M


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Comment by Bob McDonald on September 23, 2012 at 6:25pm

Good stuff to share Doug. I'm almost positive that your aircraft will not be the only one out there with this potential issue. Big time safety for other builders to take note of..."a picture is worth a thousand words". You posted two !

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