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sprague bearing

H

helithumper

Joined Nov 2010
235 Posts | 17+
montreal,Canada
So I'm looking for some info forMy 2005 fs650e about the sprague gear( starter one way bearing ).

I decided that since it's winter here I would takle the starting issue with my bike. For about half the summer my bike would'nt start with the e-starter button, the starter would just spin freely, So I checked the torque limiter gear by checking the torque and all was good. so I replaced the one way bearing in the starter freewheel gear (sprague gear) and to my suprize the starter motor still spins freely.

I have done alot of research on this subject and it seems to be that everyone says to change the inner gear. My problem is that I can't see any wear on the inner gear, it's perfectly smooth. I can see some slight wear on the outer gear but nothing that would make me think that this was the problem. for the people who have replaced the inner gear what did it look like when you replaced it, was there definite signs of scoring.
 
Hi

So you have a new OEM sprag, then that part is covered.

In a perfect world the tolerace of gears would be - Inner Race Outer Diameter +0,008 / -0,005 Outer Race Inner Diameter +- 0,013 [mm]. Most of the times this will survive with more wear then this.

What was the torque of the clutch gear assemb. ?
Have you checked if the clutch material is correctly bonded to the bigger gear ?

If you auto decomp has a weak spring or has wear, the bike will have more compression that was suposed and the starter won't be strong enough.

:cheers:
ZAGA
 
For the torque limiter gear I reglued the clutch plate back on the gear and I added a shim on the bolt side, then I set the break away torque to 30ft lbs.
If I remove the side cover and try to start the bike the srague gear spins freely. I replaced the sprague bearing with an OEM one not the two gears.

I will measure the two gears and see what I get. I'm assuming your working with .MM measurements
 
The gears should be ok, they have to take a lot of bad treatment to go wrong.

With the gears in your hand you try to turn it in one direction and the other. If everything is ok you can turn it one way and can't the other way.

just try this

:cheers:
ZAGA
 
when assembled it works fine with hand pressure. but when on the bike it just breaks free. I measured the outer diameter of the inner gear and got 1.5593"-1.5604" sorry I measure in IN". the difference between the two numbers would be 0.02794 MM and it's tapered. so this could be my problem. See pics. you can see how the inner gear is tappered towards the center of the contact patch. You can also see the outer gear has some wear marks on it but there superficial.
 

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I've had the same problem with my past two Bergs and simply shortened the retainer spring that holds the many cams by about 1/2". It works excellent! As the following article says, make sure you put the assembly back in the proper direction. (Take note or mark the inner sprag assembly before taking it apart). I thought I took notes but can't find them pertaining to the total length of the spring after I cut it. Seems it was 130mm. If you haven't tossed our old sprag assembly, you now have a spare spring!

Here's a link to explain what I'm talking about.
http://www.mad-ducati.com/Technical/Sta ... lutch.html

Here's a link within the link that I find interesting.
https://ccrma.stanford.edu/~peer/Duc/du ... pring.html
 
I tried to shorten the spring but only by 5-6 coils. I will try to take some more off as I have two sprague bearings lying around. thanks for the help
 
Hi

Taffy sells one kit with a shorter spring, that I'm using, so I didn't took the time to measure the diference between them.

My only doubt is that you have a new sprag and I never eared that problem with a new one ??
Maybe it will help with the contact of the inner race and compensate some of the wear ??

This are disengaging type sprages, they usualy disengage at 1.600 rpm, with the stronger spring it will disengage a bit latter, because when the engine is runing the cams don't make contact with the inner race

:cheers:
ZAGA
 
so I shortened the spring for the sprague bearing to 130mm and it still spins. oddly though the outer gear is the only thing spinning,the bearing and the inner gear are not moving which makes me think that the issue is with the outer gear because if the inner gear was the issue the outer gear and the bearing would spin. don't know what else to try but to start replacing parts!!!
 
Try to take out the sparck plug and hit the button and see what happens
:cheers:
 
the spark plug has been out the whole time I just forgot to mention it. I'm probably going to buy the inner and outer gears this way it's a new complete sprague.
 
That's not a cheap repair :mrgreen:

Why don't you open again the clutch first and check it, just to take the doubts

:cheers:
 
helithumper said:
the side cover is off!! I just don't know what to check anymore.
Click to expand...

Good suggestion.
You can see what bit is slipping if you stab the starter with the clutch cover off.
 
Already spun it with the side cover off and it's the outer gear that spins. the bearing and the inner gear stay stationary. I found both gears on KTM-parts.com for 135$ USD.
 
making the spring tighter only pulls it into the center more which, if all things are right, the outer will then rotate the cams (bearing to you) in to engage the inner. if the cam inner part is worn flat, it makes it hard to grab the inner gear and the freewheel will not stay engaged to the outer, thus the outer is all that spins. and by the way, a 40mm fork seal worked great, but didn't last long on my '02 650. the only solution for me was a new freewheel assy. have you tried scuffing up the inner and outer races to see if that helps? and fwiw, my outer gear looked worse than yours.
attached is a pic of a well worn freewheel cam.
[attachment=0:36eaqdyy]freewheel.jpg[/attachment:36eaqdyy]
 

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NED37, When you say you replaced the freewheel assy, you're talking about the bearing right". Mine has a new bearing but it still slips, I also took the old spring and cut it to 130mm with no better results. I will try scuffing up the surfaces because on the outer gear the surface where the bearing or (cams) would contact the outer gear surface it's polished smooth but on the non contact surfaces of the outer gear there are still machining grooves which would be a rougher surface. you can see what I mean from the picture.
 

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the freewheel assy (80040026000) is not a bearing. it is a ring of spring retained cams that rotate from the open position to the grab position when the outer gear starts to rotate (the oneway clutch action). they rotate back to open when the small gear that engages the clutch goes faster than the outer or large gear which engages the starter (the freewheel action).[attachment=0:2x6996t4]freewheel cam (3).JPG[/attachment:2x6996t4]
if you have replaced the freewheel and it doesn't grab, there is either a problem with the surface of the outer gear race or the inner gear race, or you got a freewheel that binds for some reason (not likely since it works in your hand)
out of curiosity, does your new freewheel have flats on the cams on the inside of the freewheel? i never looked when i replaced them.
 

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my freewheel cams show small flat spots on them but nothing like what's in your picture. I have also been messing with this for a couple of weeks so maybe it's slight wear from constant starting to see what parts are slipping. I will check with a 0.020" scribe to see if I can feel a flat spot or it it only visual.
 
Helithumper

You have a new sprague, your gears looks good (I have seen them with much more wear and working) you have your plug out (no compression problem), just can't think what the problem might be ???? Sorry

Have you check those little bearings (HK I think) that are in the engine casing ? Just one stupid idea, because I don't have more.

:cheers:
ZAGA
 

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