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failing starter clutch?

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Yep thats how it acts! Hit the button and it sounds like it's slipping. Anyone had this problem?

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There are two clutches in the starter system.

The one way sprag clutch that is attached to the flywheel. Never seen this one fail.

And the torque limiting clutch that connects the starter to the idler gear.

There have been TQ limiter clutches that the snap ring failed, allowing the pack to come apart..and slip.

Remove the three screws from the TQ limiter cover, and check the clutch. If it came apart, you’ll need a new (used) one, compressing the clutch pack and installing a new snap ring is very, very difficult without a JIG, press and full understanding of how the clutch is assembled and parts fixed to the shaft. I know of only three users here that have successfully reassembled a starter TQ limiter clutch, and one is currently in Afghanistan.

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are the TQ limiter clutches something that you would find or buy used? Would you just op for a new one? I will pull the side cover and check it out and make sure the loctite is doing it's job.

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I had my sprag clutch not fail but explode when trying to start my bike. Mind you this is with a BB/stroker combo with RHC 187 cams with no auto decomp and I have a YTZ10 battery. I don't know if the torque limiting clutch had failed or whether there was another problem in there. Generally the one way clutch should not slip because it is a mechanical clutch.

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I see now by looking at the last link that Eric included shows the TQ clutch apart, no doubt this is the problem. The one way sprague is still working as it should. Cheap fix and easy to swap! Look for a follow up later.

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Yep thats how it acts! Hit the button and it sounds like it's slipping. Anyone had this problem?

Mine did that when I first tried to start it last March.

I made a tool to test the torque limiter (filed slots in a tube to grip one end with other end in a vice). It slipped at 28 lb-ft, within specs of 21.5 - 40. So I put it back together and it worked and still is. I suspect the torque limiter was slipping before but by torquing it slowly on the bench got it to grab.

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Installed a road tested good starter clutch and the problem is unchanged. When i hit the button starter motor turns and will roll the engine over on occasion. Time to pull the side cover.

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Installed a road tested good starter clutch and the problem is unchanged. When i hit the button starter motor turns and will roll the engine over on occasion. Time to pull the side cover.

Yes pull the left side cover, and see if the flywheel / starter gear bolts are sheared.

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It's like pulling into the parking lot of the dentist office, you know there is nothing good happening inside!

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so I found time to pull this thing apart and inspect everything. The starter and shaft are good, starter clutch is good, spur gear is good, all teeth on the ring gear are good, and the sprague gear seems to be working. The only thing sketch is two of the starter clutch bolts took little effort to break loose and there is end play that allows the ring gear to float on the crank shaft. Ideas? Thanks in advance.

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failing starter clutch?

Yep thats how it acts! Hit the button and it sounds like it's slipping. Anyone had this problem?

Installed a road tested good starter clutch and the problem is unchanged. When i hit the button starter motor turns and will roll the engine over on occasion. Time to pull the side cover.
so I found time to pull this thing apart and inspect everything. The starter and shaft are good, starter clutch is good, spur gear is good, all teeth on the ring gear are good, and the sprague gear seems to be working. The only thing sketch is two of the starter clutch bolts took little effort to break loose and there is end play that allows the ring gear to float on the crank shaft. Ideas? Thanks in advance.

The gear is supposed to float laterally a bit so no worries on that.

It runs when started? YES??? So that knocks out the flywheel spinning on the crank shaft.

Other than that.. I really don’t know.....

Starter has it's gear pressed on to the shaft of the starter motor.. Never seen that press fit fail.. But it could.

Starter motor gear physically fits to the TQ limiter, .. the TQ limiter could fail, and have read about a few.. but you say yours is good... sooo.

TQ limiter has a physical fit to the idler gear, that’s just a hunk of steel. so it's either good or not.

Idler gear has a physical fit to the flywheel starter gear.. no way really for that to fail.

Flywheel starter gear by way of the sprag clutch fits to the flywheel.

In 9 years here , I've read one post of a sprag clutch failing.. But again you say yours is working..

Sprag clutch fits to the flywheel.. Which physically attaches to the crank by way of a pressed taper shaft and woodruf key.

That connection has been seen to fail, mostly on crappy fitting aftermarket light weight flywheels produced by a US company who makes great ideas and products but has crappy QAQC.. :lol: (I’m not bitter, I just have a long memory) Seen a few fail on built motors (my own included). But over all very rare..

That’s it, that’s all there is,, Starter turns the TQ limiter, which turns the idler gear, which turns the flywheel starter gear, which turns the sprag clutch, which turns the flywheel, which turns the crank….. If the starter is turning and the crank is not…..it HAS to be one of the above connection points.

Start with a fresh look and mind set.. I would start at the starter motor.

-Confirm starter motor is spinning under power.

Check the gear at the end of the shaft for damage.

-Clamp the TQ limiter in a set of vice soft jaws, check that it has the required amount of TQ (resistance) between the dive and driven sides.

-Idler gear present?

-Flywheel starter gear and Sprag clutch present? Working to engage and lock to the flywheel when turned the proper direction?

-flywheel attachment to the crank.. Clamping nut tight? If motor starts, it’s not likely the woodruff key is sheared and the taper fit broken, allowing the flywheel to spin on the crank.. If so, ignition timing would be off and the motor would not start.

Another question? When did this start? Anything happen just before? Parts or repairs done changed?

Edited by E.Marquez

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I will start with the last Q's first. This started over a year ago but I have ridden it very little because of it,maybe 1k. 6k before the starter bolts took out the stator and I pulled the engine and went through it but didn't split the cases. The only part changed is the TQ clutch for a known good used one.

When I hit the button the starter will free spin half the time and then suddenly grab the ring gear and as it is cranking it will intermittently start slipping, meaning I can hear the starter motor still turning without interuption but it's not free wheeling as if it is dissengaged from the crank shaft. This is what brought me to my posting title of a failling starter clutch. I thought that when I got in there I would find broken or worn off teeth on the ring gear or a split case that allowed something to move or something obvious. I have been comparing wear marks on the teeth throughout and can't find any alignment issues and nothing in the oil filter or screens. I will start down your list and see if I can find anything.

There is a vid under "ktm sxc bad starter" on YT that sounds very similar. My situation is unchanged by ambient temp and engine temp or ride duration between restarts btw.

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Bronco, just re-reading your your post, how is the gear on the end of the starter motor shaft attached? I thought the teeth are milled into the shaft, not so?

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Bronco, just re-reading your your post, how is the gear on the end of the starter motor shaft attached? I thought the teeth are milled into the shaft, not so?

You are correct, it's never been an issue I have looked at closely.. I should have said damage, not attachment.

Having never had a starter apart to the INSIDE the armature level,only as far as the outside of the armature..

attachment.php?attachmentid=17318&stc=1&d=1322733537

So I can only assume the shaft is a single piece from one end of the armature to the other... It's possible the broached gear end is attached to the shaft someplace inside the starter...so why I said attached,,, but damaged is a better choice.

attachment.php?attachmentid=17319&stc=1&d=1322733537

:lol:

Starter shim.jpg

starter.JPG

Edited by E.Marquez

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The description is a failing sprague clutch. How do you know it's good?

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good question Noble, bottom line is I can't say for an absolute fact that it is good under it's normal operating load. Without the ability to produce a cut away side cover I would never be able to see what's going on. Do you have any testing ideas? I am at that point where I have to decide to throw money and parts at it to cure the problem. What would you do next?

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Idea- YES. You are absolutely right, you need a cut-a-way cover. There must be some one here with a big hole in one from a shift lever incident willing to provide you a cover.

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There is a big hole in the cover already, and a smaller one in the top.. From either you should be able to see the flywheel turning...OR NOT.

But ya a cut away cover would be a great idea as well :lol:

The sprag clutch should show signs of damage if it's not working.. The drive gear bearing surface will likely show damage as well. Spalling, flat surface on a bearing, drag marks on the bearing surface of the gear, something.....

Both of course require removing the flywheel, which requires the use of the correct puller.. about $40 on ebay last I looked. Little more from Motion Pro

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A cut-a-way cover would allow view of the ring gear and the flywheel at the same time. Easy to see if the sprague is slipping. Yes I agree, inspection of the sprague would show evidence of damage if it is slipping. I'm wondering if debris from the chewed up stator incident is at the root of this.

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