Replacing a sprag clutch on a Yamaha TTR250

DISCLAIMER: The modifications described in the following text are for educational purposes only. In no way do I recommend that you apply these modifications to your own motorcycle. If you do choose to go ahead and modify your motorcycle based on the information in this document you will accept all responsibility for your own actions. The author(s) of this document, and host(s) providing it for you, accept no responsibility whatsoever. If you are unqualified to make any of the changes described herein but are bent on doing the modification, seek out a knowledgeable friend or professional mechanic for assistance.

Replacing a sprag clutch on a Yamaha TTR250

It's a pretty simple operation. Just follow this step by step pictorial guide.

Tools needed:- socket set, Allen socket, big plain screwdriver and torque wrench. It would be preferable to have a flywheel puller and holder but if that isn't available the rear axle can be used instead.

Parts/supplies: Sprag clutch Part # 4GY-15590-00-00 and possibly generator cover gasket Part # 4GY-15451-00-00

The sprag on this TTR was making a horrible bang on switch off and was in dire need of replacement.

Firstly drain the engine oil if you are going to do the job with the TTR in an upright position. Else turn off the petrol and lay it on its side.

Remove the starter gear cover and gear change lever.


The gear change lever will come off a lot easier if you open it up with a big plain screwdriver as shown below.


A previous owner must have stripped it down before as the starter cover's retaining bolts were butchered and had to be removed with a hammer and cold chisel.


I was lucky as the large idler gear was in excellent condition

 

At this point I realised that I hadn't drained the oil so I put the TTR on its side to carry on with the job.

Next, remove the Allen bolts holding on the generator cover.

I made up a cardboard template to hold the bolts in the correct positions as they are different lengths.

With the generator cover off, you can examine the small idler gear.

Mine was in perfect condition so I had caught the worn sprag in time.

Hold the flywheel and undo the 14mm flywheel bolt.

Next use the flywheel puller to remove the flywheel.

To remove the sprag clutch, undo the six Allen bolts.

The sprag clutch revealed!

 

Confirmation that the sprag clutch was in need of replacement was that it had seized on the big gear boss and needed some persuasion to come off.

I put it in the vice and used a large screwdriver between two bolts to turn the sprag and un-jam its teeth.

Once removed the old sprag fell apart. New sprag in packet on the right.

Before replacing the sprag have a good look around at the dismantled parts.

Particularly check the boss on the large starter gear.

If the boss is damaged you will need to replace the gear.

The reason the sprag fell apart was that most of the retaining tabs had broken off.

Fit the new sprag and make sure the bolts are torqued up to 10Nm

 

Quite often the gasket remains in one piece but I wasn't quite so lucky and had to scrape off bits of the old broken gasket and fit a new one.

Fit the new one "dry".


Use plenty of clean new oil on the new sprag and other moving parts as you proceed through the reassembly procedure.

Replace the large starter gear and flywheel being careful not to dislodge the Woodruff key on the crankshaft.

Torque the flywheel bolt up to 60Nm.

Replace the generator cover making sure the two dowels are in place to properly locate it.

Torque up the bolts to 10Nm.

Replace the starter cover. I used hex-headed bolts to make removal easier in the future.

Torque them up to 10Nm.

Refill with oil if you had drained the engine and start the TTR up and test your new sprag. Hopefully the bang has been replaced with a gentle clunk.

Job done!

Brian Sussex

 

Compiled by Brian Sussex, Devon, UK

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