Mattman4494
New Member
I recently had a rotary gear failure after fully rebuilding my Rotax 720. For the rebuild I used brand new wsm parts, but left the rv shaft assembly original because it was still in good shape.
The rv gear was completely stripped after approx. 20 hours on the rebuild. I tore the engine apart and inspected everything. Unfortunately I couldn’t find a smoking gun so I ordered a new rv shaft assembly from WSM thinking that should take care of any issues…wrong.
After installing the WSM rv shaft the crank is now binding when I try to turn it over by hand. Brass Gear is cut off center by .004”. Call up WSM and apparently this is a known issue. Only advice is to return and buy a OEM rv gear. $85 for just the gear.. ouch.
So I purchase the oem gear and install it onto my original rv shaft (My original rv shaft was still perfectly straight). Reassemble the engine and it’s all turning smoothly now. Rv backlash seems consistent. I’m happy and put everything back together for one last ride before fall sets in here in Indiana.
Ski runs great on the lake. Probably ride it for about an hour before calling it a day. So far so good… then I get home and see some glitter in the rv oil lines.. drain some oil out and sure enough the brass glitter is back after only 1 hour of runtime.
Not sure what to do now. I’m suspicious of the WSM crank, but don’t really have any way to test it. I did measure the crank for deviation and that all checked out. My hunch is the rv gear on the crank is slightly off center or not cut right. Thoughts?
The rv gear was completely stripped after approx. 20 hours on the rebuild. I tore the engine apart and inspected everything. Unfortunately I couldn’t find a smoking gun so I ordered a new rv shaft assembly from WSM thinking that should take care of any issues…wrong.
After installing the WSM rv shaft the crank is now binding when I try to turn it over by hand. Brass Gear is cut off center by .004”. Call up WSM and apparently this is a known issue. Only advice is to return and buy a OEM rv gear. $85 for just the gear.. ouch.
So I purchase the oem gear and install it onto my original rv shaft (My original rv shaft was still perfectly straight). Reassemble the engine and it’s all turning smoothly now. Rv backlash seems consistent. I’m happy and put everything back together for one last ride before fall sets in here in Indiana.
Ski runs great on the lake. Probably ride it for about an hour before calling it a day. So far so good… then I get home and see some glitter in the rv oil lines.. drain some oil out and sure enough the brass glitter is back after only 1 hour of runtime.
Not sure what to do now. I’m suspicious of the WSM crank, but don’t really have any way to test it. I did measure the crank for deviation and that all checked out. My hunch is the rv gear on the crank is slightly off center or not cut right. Thoughts?