Hi all,
This is the copy of the message I just posted on the Rotax forum:
Rotax has recently introduced a new fly wheel hub with lengthened trigger cams
which change the ignition timing during starting. This is described in
SI-912-020
R4, section 74-00-00, page 1 and 4. With the new hub, ignition timing during
the starting phase will be 3 degrees after TDC instead of 4 degrees before
TDC. I am very interested in doing this mod on my 912ULS as it should prevent
any possibility of kicking back.
However I am puzzled by the dimensions shown on the drawing on page 4. The
drawing
says the old cams are 22 mm long and the new ones are 29 mm long. I measured
the length of the cams on my 6 year old engine: they are 30 mm long! I also
did the maths: the radius of the flywheel cams is 78 mm, so 1 degree rotation
moves the cam edges 1.36 mm. From 4 to 26 degrees, that is 22 degrees
difference,
the length should be 1.36x22=29.95. So i believe my hub is good and the
Rotax drawing is wrong.
I have 2 questions:
- to anyone who has access to the back of his engine: could you please remove
the
3 screws which hold the plastic cover and measure the developed length of
the cams.
- to any one who have the new flywheel hub: please do the same. According to the
SI, engines fitted with the new flywheel hub start with the following serial
numbers:
912S: from S/N 4,923,847
912ULS and ULSFR: from 6,775,360
Waiting for your answers
Regards
Remi Guerner
F-FGKL
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http://forums.matronics.com/viewtopic.php?p=324674#324674
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