Can a sprag clutch wear out?
 

My 03 FSE450 has a new interesting problem, seems the sprag clutch isn't making enough grip to spin the motor thru the compression stoke. I have pulled it apart and it has no cracks or broken parts. The valves are in spec and the auto decomp is working. It spins at about 25 psi compression.

Never heard of that. Have you watched it with the casing off to check it is the sprag not a gear damaged or misaligned?

You can buy sprags from some engineering suppliers at about a 1/3 of the price from GasGas.

it is possible that the sprague can wear out. what i think usually happens is the decomp wears out so you dont get the right amount of lift but more important than the amount of lift is the timing of the lift. just my experience from non-gasgas four strokes

I?ve had that same problem for some time now when it?s cold weather. Well today it completely stopped spinning the engine, only the startmotor spins when i press the start button.

It was guite a problem because my kickstarter doesn?t work and I was about 5 kilometers away from home. I got the bike running by pushing it but it was a lot of work because of icy roads.

Does anybody know if some other bikes parts fits in? It?s hard to get GG parts here in Finland(And the original parts are also over priced). I happen to know that DR-Zs ignition clutch doesn?t fit... It might be fittable with some work but I?d rather buy straight fit part...

Cold weather could cause the grease to get hard and prevent the sprag from working properly. Did it work right once it was warmed up?

Yes, after warming up it worked fine. But now it doesn?t work at all, no matter of temperature. I?m pretty sure that I need new starter clutch. I rebuilded the engine last summer and it was pretty worn looking already then.

I have used sprague clutches on packaging machines for years. They do eventually wear out. The sprags develop a small flat spot that keeps them from rocking into lockup. It takes a long time for this to happen.

There is normally a spring around the perimeter of the sprags that holds them under tension. This tension provides the grip so they respond quickly. You can get a bit more life out of them by shortening the spring but it's tricky to get right.

Thick, cold oil will make it harder for them to lock up. If you ride in cold weather, thinner oil will help. Usually there is some sort of slip clutch in the starter system that loses friction as time goes by. The slip clutch is often what gives trouble well before the sprag clutch. Some slip clutches can be taken apart and shimmed for higher torque.

A sprag clutch is primarily an over-running device. It allows one element to be stationary while the other rotates around it. The sprag clutch is needed to let the drive gears spin at motor speed when the engine is running (while the starter gear is stationary). Thus the over-running function.

Note that cam shape of the individual sprags allows lockup when the starter motor is driving the gearing. Sprag clutches are also known as one-way clutches.

A bendix style starter arrangement has the gearing move into engagement while cranking, then it moves back to release when the operator stops using the starter button.

Mine went on my FSE400 , the engine was just spinning over.
My solution was to get rid of the bike as i was sick to death of trying to find spares and them costing a bloody fortune.:eek: As much as i loved the bike im glad its gone. Still have Gasser trials bike so not a complete turncoat :)

I just ordered a flywheel puller so I can take my starter mechanism a part. Had to got my flywheel taken out by shop last summer when I rebuild my engine.

I found out that Stieber makes all kinds off sprags and they are alot cheaper than OEM part. I am going to take my Gassers sprag to local bearing dealer and replace it with stieber clutch, if there is a same size and torque available.

I will post how it goes and tell the part number if I find a replacement that works.