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Sprag Clutch
Some manuals refer to the sprag clutch as the Starter clutch.
The two terms are interchangable.
Starting the engine repeatedly with a flat battery can kill the sprag clutch. When its gone, when you try to start the engine it just makes a loud clicking rattling sound.
The only solution is to change it.

Undo the sump drain nut.
If you use a ring spanner you can lift the nut out the way without dropping it into the oil and you wont fill up your ratchet with old engine oil.
If you have just flushed the oil and the engine has been running, its going to be f*cking hot.
Lift the starter cover off.
The idler gear should turn anti clockwise freely and not turn in the other direction. Inspect all the teeth, make sure they are in good condition. If there are teeth missing they will be in the engine somewhere and thats a bad thing.
Remove the 6 bolts holding the starter cover. Seperate it carefully as the paper gasket will be stuck to both faces.
There are little flanges around the cover to allow you to lever it with care.
Have a cloth ready to wipe up the little puddles of oil that will run out.
Remove the thrust washer.
Slide off the idler gear. The bearing should remain inside it.
Remove the red wave washer. There are two of these to remove, this is the smaller one and they are both colour coded.
Dont get them mixed up!
Slide out the shaft.
Take out the starter cover positioning dowels so they dont drop out and get lost or damaged.
You can see part of the intermediate gear.
The gear should turn clockwise freely and not at all in the other direction.
Inspect the teeth in the spline of the starter motor and make sure that none are damaged and give it all a good wipe out.
Remove the thrust washer 2.
Now undo the bolts on the right engine cover.
You dont need to undo the timing inspection cap for this, it will remain in the engine cover.
Take car of the top bolt shown in the picture. It is different to the others and has a rubber seal on it.
Slide out and check the bearing in the Idler gear and make sure its not damaged. Its not going to be reused but you dont want to be leaving any broken needles behind in the engine.
Remove the wave washer. This is the bigger one of the two and should be colour coded blue.
Slide off the intermediate gear. Note which way round it goes, the two sets of teeth have different pitches.
Remove the cover. You may need to wiggle it a bit and prise it off with the little flanges like the starter cover.
The paper gasket will most likely be stuck to both faces.

The main gear should turn anti clockwise freely, but not clockwise.
Hold the sprag clutch to prevent it from turning either the specific triumph tool or a home engineered one (this is the triumph tool in the picture) and loosen the nut with a breaker bar.
Remove the nut and washer
Slide out the shaft.
If it doesnt come off as one and drops apart, dont drop the bearing.
Remove the large thrust washer.
Remove the sprag clutch assembly. You can slide it off in one part keeping it all together which is probably better, but Ive done it in two for the pictures so you can see how it goes together. They sit together with a bearing thats held between the hub gear and the clutch assembly.
All the bits laid out in some sort of order.
The three parts of the offending dead sprag clutch. You must replace all three parts as they are matched and wear together. Replacing just one part will likely cause it to fail again in very short time.

A new sprag clutch assembly is £285 plus VAT from Triumph.
So I rang the ever helpful Sandy from WWW.TRIUMPH-ANT.CO.UK a UK triumph specialist breaker.
He came to my rescue with a complete sprag clutch assembly and bearing for £110 including postage.
Thanks once again Sandy.
Check the bearings in the sprag clutch assembly to make sure all the needles are there
Replace the thrust washer, new sprag assembly and reverse order.
Threadlock on the bolt. You DONT want this working lose
Hold the sprag assembly with the triumph tool and torque it up to 54Nm
Make sure all the engine cover dowels are in place.
Put a smear of rubber grease around the seal for the starter motor to ensure water doesnt get in.
Torque up all the bolts on the engine cover evenly making sure not to forget to take extra care on the one with the seal.
The handbook states 9Nm torque for them, but this is almost finger tight, so I do mine up at 12Nm.
Replace the intermediate gear, blue wave washer in reverse order and fit the new gasket.

Coat the new gasket in clean oil on both sides before putting it in place. Not only does it stick in place better making it easy to fit, but it will come off the machined faces easier when you split them next time.
Idler gear, thrust washer, red wave washer and new gasket in place.
And torque up all the bolts on the starter cover to 12Nm the same as the engine cover.

Fresh engine oil and then its job done.
Put the dowels in and the shaft in place

Slide the thrust washer on

Slide the bearing on the shaft.