Stepper Valve

Part #5001971

What's inside, What not to do, How to fix it.


If you remove it and then plug it in and turn on the bike,

it launches the small parts to the right. It's not the end of

the world, though...



Left; all the parts. Right, view into the stepper.



The stepper 'fix' procedure is at the bottom of the

page, and isn't terribly involved. This was my journey

of discovery that totally destroyed my stepper, but

revealed how to save yours.


The case is held together by these little rivet things.


After grinding off the rivets and driving them into the

case, this is what you find: it's a little stepper motor with

no user serviceable components...


The tiny wires are motor winding wires. Not stranded wire

they break with ridiculous ease. Another bad thing.



Left, good view of the tiny wires. Right, the posts they are

soldered to. I was able to resolder the one that broke, but

the length is critical. The shortest one breaks, of course, and

then it no longer reaches after you fix it.



What appears to be a screw on the stepper valve is: it's a

lead screw. The small grey part in the stepper motor acts

like a nut on the lead screw thread. The motor spins it and

the shaft is extended or retracted. The shaft can't turn due

to the fit with the white plastic collar visible in the first 2 pix.


Do This!

If you have already launched the little parts, but have not yet

torn the thing apart destroying it completely, here is my advice;

Put the spring on, then the collar. Push the collar down so you can

see the white plastic part the plunger goes into. Align the lead screw

so that the flanges and slots fit together and PUSH. Wiggle it a bit

to get things going if you have to. You should be able to get the lead

screw to spin the nut and reinsert itself. Now put it back in the bike

and turn on the power. The stepper will go out a good bit, then back

in a short way. Turn the bike off, then turn the bike back on. The

Stepper can take 3 cycles to get to the fully extended position. When

it's back all the way out, you should be back in business! Cool!!


The Theory

The stepper is a simple unit with no internal homing system. In order

to find home, the computer steps it out a little further than it ever goes

in normal use. When the plunger bottoms in the housing, the stepper

motor tries to keep moving it out, but just slips back electrically. The

plunger is pressed against the stop, fully closed. Now the computer knows

where the stepper is, and counts steps backwards from there to go to the

calculated position. The problem is that when the stepper is not in the

housing, the lead screw runs out of length and the spring launches everything.

Questions or comments?

Email me!