912 Gearbox

[Av8r3400 1178]

Here is the rebuild of the disc spring in the gearbox off my 912UL Rotax motor.

 

 

 

First is the removal of the fuel pump.

 

 

 

 

Using a rubber mallet you loosen the gear box from the locating dowel pins

 

 

 

This is the engine side of the box.

 

 

 

This is the driven side of the box.

 

 

 

Here are the internal components of the driven side of the box.  Fifth from the right are the two cupped shaped washers that make up the "disc spring", which holds pressure on the assembly.

 

 

 

The old washers are .2015 and .203" thick.  The new ones are .2145 and .2215 thick.  Quite a difference.  I'll take some more photos of the reassembly and hopefully successful results tomorrow.

Edited 19 Sep 2013 by Av8r3400

[dholly 718]

Real interested in seeing the procedure, cost and subjective result for this. Gearbox still ok here at only 180hrs, knock wood, but I'm sure it will be in my future someday.

[Av8r3400 1178]

I did the whole reassemble in reverse order thing today.  There really wasn't anything to photograph with that, so...

 

I did take a couple of shots of the press tool used to disassemble the gear box shaft assembly.

 

This tool is intended for the "B" Rotax 2-stroke box.  This is the same tool they use at LEAF, too.  They told me they modified it to fit the 912 box.  I didn't want to modify the tool (it isn't mine) so I made some shims to help it fit the larger gear better.

 

 

 

Here is what the tool looks like by itself on the gear.

 

 

Here is with the shims to spread out the force on the gear a little more.

 

 

You put the assembly in the press, supporting the prop flange and then press on this bridge until the retainer clips release.  Easy peasy.

[C5Engineer 1170]

Larry what was the issue that prompted this job?

[Av8r3400 1178]

The ever worsening vibration at low rpm. After fixing the carbs to death, this was the only other option.

[Av8r3400 1178]

Well, it didn't help.  The Vibration is just as bad as ever.

 

Monday I start making phone calls.  LEAF, Lockwood and anyone else I can think of.  I had my EAA Chapter meeting today.  One of our members works for Bombardier.  I had a long discussion with him.  I got some ideas.  More work to come.

[akflyer 1427]

Do you have the soft start module?  I am sure you have looked at plugs, but are they clean?  Have you put on new plug wires?  I had a vibration/ rough spot in mine that was driving me nuts, but new plug wires cured it.  It seems that if I don't change the plugs every 25 hrs or so it starts running rough, even though the plugs look great!  I went to iridium plugs this time and am around 15 hrs and so far so good, will see the next time I am home hopefully as I swing past that 25 hr mark.

 

[Av8r3400 1178]

I don't have the soft start module on my motor.  On the 80 hp motors the lower compression doesn't require this feature for a smooth start.

 

On the 912 they suggest that plugs be changed every 100 hours.  This is quite conservative, they easily are still good at 150 or even 200 hours.  Mine currently have about 20 on them.

 

Plug wires, on the other hand, may be something to investigate...