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losiu 04-17-2007 01:03 PM

LC4 640 starter clutch fix
First of all, I’d like to thank Beez who inspired me to do the work described below. Based on his description of the problem which he had posted on an e-starter thread, it sounded like the same problem I had been having:


Originally Posted by Beez
I had the starter clutch go on my '97 620. Kicked it for a couple of years before I finally got it fixed. I've heard this problem many times here and on KTMtalk so it seems to be a weak point on LC4s. If this is your problem the starter will turn fine but you will hear a loud, horrible KLaaccKK! KLaaccKK!

He also sent me an interesting PM in which he told me that, supposedly, the starter clutch could be fixed with the right sized spring from an O-ring seal.

Let’s get to work then !!

I am not a professional mechanic nor do I have the repair manual for LC4s. I did this based on my experience working on the LC4s I’ve had (and some luck).

The tools needed to do the work are very basic. There are two things that I can think of that are an absolute necessity to do the work right: beer and the flywheel puller.

The first one is probably readily available where you are. The puller might be a little harder to get. I was lucky because my buddy had one made for him when he was rebuilding his engine. He kindly lent it to me and I can tell you right now that if you don’t have this particular tool, it is probably impossible to do the work.

No.7 on the diagram below is the part you need to get to.

1.You have to unscrew the flywheel cover (with the stator inside) on the right.

It’s a good idea to find the TDC and then take out a bolt from the front of the engine to lock the crankshaft in place. In order to do that, you need to take off the thick washer that sits on this bolt, and screw the bolt back in. You might need to try a few times moving the crankshaft back and forth a little to hit the right spot. When the piston is in TDC, the bolt goes right in and locks the crankshaft in place.

2.You don’t have take anything else off at this point. I was doing it for the first time and to make sure I was doing the right thing, I took the e-starter out and basically, the whole right side of the engine (this is NOT necessary to do the repair). It’s at this stage that you’ll need the puller.

3.When the flywheel is off, you’ll notice another “wheel” attached to it with 6 screws. Again, I took it apart to take a closer look but it doesn’t need to be done to get to the faulty part.

If you turn the flywheel over, you’ll see this:

4.You need to use pliers to get the starter clutch out. It looks like a kind of bearing at first, but when it’s pulled out, it looks like this:

5. What you see above are irregular shaped metal blocks held in place within a metal ring by a spring. The spring was so loose that one of the metal blocks slid out of its place and looks like it's missing.
Put the whole thing flat on the table to take off the spring without losing the metal blocks. You also need to make sure that the blocks don’t turn in any way when you put the new spring back on.

6.You can see that this spring has seen better days.

7.This was the cause of the starter clutch “slipping”. The metal blocks couldn’t lock the crankshaft together with the free wheel which is spun by the starter engine. The slipping created the grating sound described earlier by Beez.

Here a problem occurred. Based on my information, the possibility of replacing the worn out spring with a spring taken from a large rubber O-ring seal was only a theory which proved to be a little trickier than expected.

8.All the springs pulled out of the rubber O-ring seals that were more or less the right size in diameter, were too thick to fit in the groove around the metal blocks. The spring has to kind of hide inside the groove and if it doesn’t, it won’t fit back in the engine. Basically it needs to be just the right size. I have no idea what diameter the original spring is when it’s new because mine was all stretched out. This element, the metal blocks and the spring, is sold as a whole unit and costs around $80. You can’t buy just the spring.

9.I got 3 rubber seals and measured the springs. The first one was clearly too thick.
Here's a pic of the one that was originally in the starter clutch:

This one turned out to be too thick:

10. I finally managed to get a seal made by a company called "ERIKS” whose measurements are 50 x 72 x 7.

The thickness was right but the diameter seemed a little small (50mm). I decided to put it in anyway because the old spring didn’t work at all and I really had nothing to lose by trying.

It worked fine and the starter works great with no weird grating or KLaaccKKing sounds.
From this point, everything is easy – put it all back together in reversed order and start your bike :D

Here's what my e-starter sounds like after the repair.
The engine was cold and I used no choke in order to let it work for a while.
Does it sound healthy or what ????

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The total cost of the repair is probably around $15 ($2 for the rubber O-ring seal and $13 for the beer)

It's also worth mentioning that the work can probably be done within 2 hours if you have the right spring :)

Good luck :)


Colemanfu 04-17-2007 04:11 PM

Very good post, great description and many pix. My junk was a bit different. Just put in a new starter ($250). I hope I never have to kick again.

DC950 04-17-2007 07:45 PM

I'm bookmarking this one. Thanks Losiu!

gunnerbuck 04-17-2007 09:50 PM

Great post, but a word of caution: On LC-4 engines with the Kokusan 4K-2 ignition it is recomended to use a flywheel holding device rather than the crank locking screw to tighten the flywheel nut. The 120 LBS torque required could damage the crank web. It's ok to use on the LC4s that only require 44lbs torque on the flywheels.

losiu 04-18-2007 04:25 AM


Originally Posted by gunnerbuck
Great post, but a word of caution: On LC-4 engines with the Kokusan 4K-2 ignition it is recomended to use a flywheel holding device rather than the crank locking screw to tighten the flywheel nut. The 120 LBS torque required could damage the crank web. It's ok to use on the LC4s that only require 44lbs torque on the flywheels.

Thanks for making this clear. When I bought this bike it needed much more work done than this. Right now it runs almost perfectly but because it required work in general, I was not afraid to do this repair.
I did worry about locking the crankshaft in place using the bolt because it's on the other side of the engine. I looked for many ways of locking the crankshaft but I failed to unscrew the nut. After locking the crankshaft with the bolt it turned out that the flywheel nut wasn't that tight.
I tried to be careful putting it all back together and the bike runs great but I agree that it's always good to have the right tools.

Thanks for bringing it up here :)


NICO 04-18-2007 05:12 AM

Good write-up. :thumb

I'd like to nominate this for the index. I have already "subscribed" to it, just in case.

Beez 04-18-2007 06:45 AM

Glad to see this worked out for you. :thumb I also nominate it for the LC4 Index.


goatherder 07-24-2007 05:42 PM

Just fixed mine and heres the repair part#
SKF Seal # 19993. Cost me $8 and the spring fit perfect. Starter works like new now. Drove the bike to European Motorsports in Spanaway and gave them $10 to remove the flywheel for me. Nice guys at that place.

So the starter works like new, and I did the fix for $18 + the fuel to drive to their shop. I didn't use a gasket...just loctite sealer to glue the stator cover back on. Time will tell if it works.

But fer now I'm happy as a pig in shit.

meat popsicle 07-25-2007 04:50 AM

Heya loisu,

you are turning out to be a handy fella - more than just wheelies! looks good to me; the only question I have is if the spring wears out, and KTM doesn't sell just it, how long until the irregularly shapped metal blocks wear out? could you see wear and tear on them?

thanks for the nominations folks. now that I finally have some time again I will be attempting an update, although reorganization may be in order due to the post size limit...


losiu 07-25-2007 11:07 PM

Hey Meat,

I don't really see the problem with the blocks. YOu can see that they've done some work but as long as they keep the right shape they're OK.
The whole unit (part no.7 in the diagram at the beginning of the 1st post) costs less than $100. The reason you might want to do the repair using a spring from a seal is to save $90 for beer or to avoid having to wait for the new starter clutch.
I have to tell you that there was another KTM in Poland that has been fixed using this info and it works great. Maybe I'll get the guy to post here. Mine has been working great ever since the repair. I think it's a good way to go.


pawel 08-22-2007 02:09 PM

it woked ok for me
as losiu was mentioning, I was having exactly the same problems with my clutch starter, and thanks to this post I was able to fix it by own spending few $ for the spring

below I am attaching few photos:
- after taking out flywheel, clutch was totally destroyed,spring was broken and those small stones was everywhere

- I realized as well that flywheel is little bit demaged, and 'stones' are not having initial/oryginal shape
but finally I have decided not make anything with flywheel, and stones, I have replaced clutch spring only, mounted everything back and till now(more than month, I am ridding almost everyday) it works fine!!!:clap

losiu, thanks for this post and help:freaky


CRW 08-31-2007 04:45 PM

When doing this are you guys draining all of your motor oil ? or just losing whats whats behind the cover and toping off?

losiu 09-01-2007 05:31 AM


Originally Posted by CRW
When doing this are you guys draining all of your motor oil ? or just losing whats whats behind the cover and toping off?

It's good to drain the oil just from the engine (you don't need to drain it from the frame). If you have a side-stand, the job will be even cleaner cuz the bike leans to the other side.


Loadedagain 09-01-2007 06:02 AM

good job man! thanks for the detail!

ChrisC 09-01-2007 07:10 AM

Great writeup Losiu!

Just to keep everyone's terminology straight, the assembly with the spring is called a "sprague (sprage, sprag) clutch". It's also called an "overrunning clutch" and is very common in automobile automatic transmissions... :deal

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