How to replace starter sprag on KTM 950/990 (LC8)

By:keener

Ignition system finally failed. On the worth place I could imagine. After trailing my bike 1200km to West Virginia from Toronto to ride TET trail. It failed right at the mouth of the trail

The symptom.
When you hit the started, it spins freely without engaging the engine. You might get some sporadic engagements but once it goes it will get worth to the point that it wont engage at all. All you hair is a whurrrrrrrr sound. it spins and spins... This might also happen if the srag is installed back ward! Daugh!

Some say, you can rock the bike back and forth in gear to get the sprag to grab. It didn't work for me.

After some research here, I was sure the culprit is the starter "sprag" clutch. There is no post that walks you through the whole thing. Info is spread all over the place, hence the reason I am making this post.

LC8 part comes with bunch of other parts (flywheel,...) that you don't need and of course it costs $575+. I learned form this post that LC4 engines uses a sprag that contains the same parts as in LC8. And for LC4 you can buy only the sprag from KTM. The beans and the spring holding them together is exactly the same as LC8. Only the housing is different. Its the spring and the beans that fail. So, you can get the LC4 sprag for about $70 take it apart and transfer the beans into your sprag on LC8 ....AND save $500.

If you don't know what a starter sprag clutch is learn more here: https://en.wikipedia.org/wiki/Sprag_clutch
in short its a one way clutch around the crank shaft that grabs the crank shaft like a vise grip only when it is rotated clockwise or counter clock wise I dont remember which. It allow the crank shaft to speed up faster than the starter, which is exactly what's needed.

Disassembling:

- Lean the bike just a bit to the right side. I did this putting a 2x4 under the left leg of the centre stand. This is enough to prevent any oil lose. No mess.

- Take the generator cover off. Some bolts are longer, two have copper washers and in the bottom hase a steel washer, remember where they go.

- Pull the crank shaft breather hose down a bit to give yourself some slack then tilt the cover and zip tie it through one of its holes to some where on the bike so it's out of your way. I covered it with a plastic back. No need to take the hose off.

- Take the one 2" gear at the top off and aside. It will eight start on the motor side or comes out with the cover. Inspect the bearings on the engine side and on the cover.

- This is a good time to replace the crank shaft seal that is on the cover (not neccessary for this job). It is cheap. You will damage the seal when you take it out, so have a new one ready. You can send the new one in with a plastic hammer and a 14mm socket. When this seal fails, you will get excessive oil spitting out of your crank shaft hose over your front carb inside your that hunk of junk air box. That's if you still have a air box and not the ITG filter, come on... the best mod ever.

- Now, the toughest part. Taking the the flywheel off the freewheel. That big ass bolt in the middle is tightened with 150nm torque and BLUE 248 loctite. Lots of it. You WILL need a strong impact gun. Try loosening it with a wrench is nearly impossible because you will turn the engine. Even on 6th gear. I got someone pressing down on the rear break and used an impact gun with my air compressor set to 150psi.

Some say don't use heat, some say do....Old manuals say use heat but make sure the flywheel won't gets hotter than 80C. I would try opening it with out heat and see what happens. If it didn't open, then use a heat gun or a hair dryer on low setting. You want to heat up the bolt and not the flywheel. There are wax and glue around the magnets inside the flywheel that you don't want to melt.

So, stick the heat gun to the bolt and periodically touch the flywheel to make sure its not too hot. As long as you can hold your hand on it for 5 second you are OK.

Get the bolt hot, this will soften the blue loctite, then use the impact gun while someone is holding the rear break and bike is in 6th gear . DO NOT use the engine locking bolt like how it is used for valve check at this stage. Manual doesn't call for it during the disassembly for a reason. It calls for it for assembly. I suspect there is danger of breaking the tip of the locking tool inside the engine.

Mine opened up nicely after heating up the bolt. The bolt was too hot to hold in hand but the flywheel was just warm.

One last thing if you use a heat gun. Int he begining I would warm up the area include the flywheel just a bit by holding the heat gun 8" away first. This prevents the risk of cracking something by heating up one piece while other parts all very cold.

nufff said.....OH don't use a blow torch.


You will need a big allen key. I don't know the size. It is the same key you would use for valve check job.


I use a T-70 torx socket because that's what I had. It worked just fine.







- Clean flywheel bolt thread form dried blue loctite.
After the flywheel bolt is out, take your sweet time and clean up the threads from left over loctite. You will have another chance once the flywheel is out. This is only to clear the path for special tools on the next step.








I held a vacuum in there while cleaning the threads so the debris won't go in the cranck shaft or get into the engine.

- Taking the flywheel out.
This is the part you either need to get creative and make tools or cough up some money to KTM for "special tools". I when half way. Bought one and made the other. They are just two screws, nothing is special about them. One is a normal M20 bolt with 30mm socket head. The other is a M16 grub screw. Here are the details:

The grub screw (push screw)has different thread pitch for earlier LC8 models.

M16, 31mm long allen head - 2.0mm thread pitch KTM part # 60029009010 “PUSH SCREW F. FLYWH. EXTRACTOR “


Cross Reference Lookup

This is supposed to be the same for all LC8 engines. But since I can't find a Special tools section for bikes past 2007, I can not confirm this for sure.











Here are two tools side by side:




Drive the grub (push) screw in the crank shaft. No too far in. It just need to clear the larger dimeter threads for the other tool. Then drive in the big screw over it (Flywheel extractor). There are threads there for both of them. The big screw will force the flywheel out. You might want to use the impact gun here again. For that you will need a 30mm socket.











- Before taking the flywheel out you might want to loosen the 6 bolts screw holding the spag. I didn't and I had to nervously put the flywheel on the vise with lots of rubber padding. These screws are supposed to NOT come off or else.... I found out they where nearly finger tight!!!! Reading on this forum later I noticed I am not the only: http://www.advrider.com/forums/showt...1#post23862711
You are supposed to replace the bolts as per the manual. I didn't! They didn't have any sign of stretching.
There is loctite 648 (green color) on these bolts. Take your time to clean and degrease them very very well. Don't forget the holes. I tried different methods to clean the holes. Finally the best one was using a 6mm tap with 1mm pitch. It works great. If you do this, screw the tap in with your fingers not a driver and go back and forth to clean the loctite. Be-careful, tap is of course made of harder material so don't go in and out a lot!

- The sprag, the culprit
Apparently my starter sprag clutch failed because the ring spring holding the beans together let go for some reason. The spring looks like the one holding the dust seals on the forks. Some of the beans showed sign of wear. They are almost oval shape. At this point you need to take the LC4 sprag apart and transfer the beans and the spring into your LC8 sprag. The only thing different between the two parts is the housing. The rest is identical. Note the direction the beans go in. They all have a cut indicating their direction. Take photos. If you install the spag backward, or install the beans backwards, your sprag with not engage. Starter will spin freely.

LC4 sprag part# 58440026000 FREE WHEEL FWD 332008 BLS

New vs. Old:

Note the direction of the beans:



- Loctite 648 (THREAD COMPOUND) – Green
use it on the 6 small screws. Manual asked to replace the bolts. They are about $6 each from KTM. Some say they could find them locally from Fastenal.


The important thing here is to use Loctite 648. Given how important it is that these screws don't come of I would not use any other loctite. It was hard to find this loctite. Only one shop locally had it. Forget about Homedepot, Autoparts, Canadian tier,...Napa could order it in. This part experiences lots of shocks from the starter. Red loctite (as some have suggested) may be harder but not be able to tolerate the shocks. Use lots of it. Read KOTH post here : http://www.ktm950.info/how/wotf/wotf.html under “Ignition Rotor”


If these bolts come off, they will destroy your generator. There are threads on advrider of riders experiencing this. It fills your engine with shredded copper wires.
My 2004 manual, calls for 13nm torque on these screws. I THINK (not sure) , some other years want 18nm from what I have read here.

Put it back together the way you found it.

- Use lots and lots of blue loctite 248 on the crank shaft bold and the mating surface:

Put the engine lock tool in on the other side just how its done during valve clearance check

Torque the big bolt to 150nm. Don't use impact gun!!! , get someone to hold the rear brack for you while bike is on the 6th gear.



- Put the cover back on and you are done.

Just a final note. Resist the urge to start the motor right away. Give it at least couple of hours if not over night to sit. This will allow the loctite compounds to set. The worth thing you can do is to break the thread locks, specially the small bolts.

Good luck!

(KOTH: Read the full thread HERE before starting on this job. You'll especially want to pay attention to the discussion on the use of loctite on the crankshaft.)

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