Wild Dog Adventure Riding

Technical Section => Make / Model Specific Discussions => KTM LC4 400/610/640 & 690 => Topic started by: igeorge on November 04, 2013, 11:58:33 am

Title: 640 Adv sprague clutch fix
Post by: igeorge on November 04, 2013, 11:58:33 am
Hi All

Some of you might be aware of a cheap fix for the fairly common starter clutch failure.  The symptom is a spinning starter that doesn't engage the flywheel, leading to much improved leg muscle tone as you slowly perfect your kick staring technique. 

While trying to prevent the odd knee through face kickback......:)

When i bought my 640, it was with such a buggered starter clutch, which I have finally fixed.  Once you have the right tools and parts, its a trivial exercise, but therein lies the rub...

A replacement clutch is ~R1000 from KTM, and before you say "JOH, thats a lot!", the forums are littered with blokes with Ducati's and BMW's that use the 'same' part,recommending the KTM part because its the cheapest...

However, the reason for the failure is that the garter spring in the clutch, which tensions all the concentric cams that make up the clutch, becomes stretched and mangled, preventing the clutch from biting on startup.  So a replacement spring can fix the clutch!  And such a spring is found in oil seals - you just need the correct spring thickness and diameter.  The diameter gives the correct tension on the cams, while the thickness of ~1,5mm is required because the spring has to fit into slots in the cams.

The forum posts I've come across mention an SKF 19778 seal - however its not brought in by SKF South Africa.  Fortunately they do bring in a SKF 19832, which has the correct spring.  Costs about R140, and you throw away all the expensive bits, and keep the R5 spring:(

The repair is simple.

1) Remove bashplate and sprocket cover.
2) Remove the ignition cover (a few drops of oil might leak out)
3) Remove bolt next to front oil filter, and insert a M6 bolt (with tapered end) into crank slot at TDC to lock crank. Some posts say this is a no-no, but KTM CT mechs confirmed this is what they do.
4) Remove flywheel nut (its a left hand thread, something to remember when your vessels are straining fit to burst but the f&$#ker just wont loosen...)
5) Use a puller to pop off the flywheel...I had to get one from KTM. (see my other post)
6) Carefully slide sprague clutch out of flywheel, remove shot spring and replace.  In fact this can be done by only lifting it out far enough to expose the spring grooves, as it prevents the cams from then falling out of the cage.  Sounds tricky but not really.
7) Push sprague back and reverse all steps back to one.  Don't forget 3!!!!! :)

8) Enjoy your electric start

Recap:
Oil Seal: SKF 19832                 R140
Puller:    KTM 58012009000     R380   (Happy to lend it out to dogs)

Cheers
Ian
Title: Re: 640 Adv sprague clutch fix
Post by: Malibu on November 04, 2013, 12:01:00 pm
I don't suppose you took any pics while doing this.... ?

:)

I'm a picture person...
Title: Re: 640 Adv sprague clutch fix
Post by: igeorge on November 04, 2013, 01:04:49 pm
Hey Malibu!

check this thread for pics: http://www.advrider.com/forums/showthread.php?t=222515 (http://www.advrider.com/forums/showthread.php?t=222515)   .... excellent description and pics there.

What is relevant to us here(in my post) is the correct seal that can be ordered over the counter.

Cheers!
Title: Re: 640 Adv sprague clutch fix
Post by: Malibu on November 04, 2013, 01:05:34 pm
Thanks!  :thumleft:
Title: Re: 640 Adv sprague clutch fix
Post by: AntonW on November 06, 2013, 09:34:56 pm
Wow, thanks.
Title: Re: 640 Adv sprague clutch fix
Post by: African child on November 06, 2013, 09:46:04 pm
Many thanks! :thumleft:
Title: Re: 640 Adv sprague clutch fix
Post by: DeeCeeBee on November 06, 2013, 10:14:27 pm
Thanks very much.
Now...what is the "cluk cluk" sound I get when I switch off the bike?
Title: Re: 640 Adv sprague clutch fix
Post by: Sprocketbek on November 06, 2013, 10:25:55 pm
I was aware of this "fix" but I decided to replace EVERYTHING.
Some parts did have signs of wear.

Each to his own.
If something goes wrong in there, you will end up with a BIG mess.
Title: Re: 640 Adv sprague clutch fix
Post by: Bob the plumber on November 08, 2013, 12:59:28 pm
Thank's Ian, very useful. You have saved me plenty boodle, which I am happy to repay with a 12 Pack - your choice. Btw, is that puller available?

kind regards

Bob
Title: Re: 640 Adv sprague clutch fix
Post by: igeorge on November 11, 2013, 12:23:33 pm
Yep, its available.  As well as the modded bolt:)

I'm in Noordhoek, and work in Westlake.  Drop me a pm and I'll give you my details.
Ian
Title: Re: 640 Adv sprague clutch fix
Post by: Doerengone on November 20, 2013, 10:11:07 pm
Cool fix igeorge. Thanks for the part numbers.

(I replaced my 640`s sprague clutch with a KTM part at about 45,000km)
Title: Re: 640 Adv sprague clutch fix
Post by: igeorge on November 21, 2013, 11:26:00 am
Can you recall if the spring seemed shot??
Title: Re: 640 Adv sprague clutch fix
Post by: Doerengone on November 21, 2013, 07:50:24 pm
I replaced the Sprague clutch because the starter would not "bite", just a noisy rattle when starter button was pressed.

I guess the spring was the culprit, as there was little noticeable wear on the rollers etc. The spring being the weak link, as the other components are pretty robust.