A forum for owners of Yamaha TTR250 trail and enduro bikes!

Members Login
Post Info TOPIC: The dreaded clunk


Member

Status: Offline
Posts: 5
Date:
The dreaded clunk
Permalink  
 


Hi Brian! Its me, Robin. Remember? the one who bought a whole bike from you, one nut and bolt at a time. Hope you are enjoying 'retirement'. I have a question but don't often use the forum so maybe its already been answered...

It's this: When turning off my 315cc bike I often get a loud clunk. Not every time. Have tried to look for a pattern but can't find a way of switching off without still getting the noise every so often. I know what the 'clunk' should sound like as my 250cc TTR is much less pronounced when it clunks. I did change the sprag clutch a few thousand miles ago, so am wondering if there is something else to try or be aware of?

Hope you or someone can help.

Cheers,

Robin



__________________


Super Guru

Status: Offline
Posts: 6402
Date:
Permalink  
 

Hi Robin - how could I forget you! biggrinbiggrinbiggrin

The sprag clutch runs on a boss on the Gear 3 which sits behind the flywheel. Could the surface of the boss be worn or damaged?

Otherwise you should be OK. Maybe leave the TTR in gear when you shut down and let the clutch out as it stops to prevent the kickback which causes the clunk.

Brian



__________________

Exeter, Devon, UK

http://www.ttr250.com  - The one and only dedicated TTR250 FAQ! 
 

http://ttr250.activeboard.com/ - THE forum for TTR250 owners



Member

Status: Offline
Posts: 5
Date:
Permalink  
 

Hi Brian,

I think I may have a solution for this one.

The edges of the sprag are worn, just at the edge, on both sides. Meaning the inner and outer sides but just on the edge confuse

Robins sprag 3.jpg


I couldn't live with the clunk any more. It sounds awful. plus I'm planning another desert trip and want the bike to be right. Didn't you say the clunk could break an internal part if left unattended to? Plus being a 315cc I wonder whether there is more force behind the noise. Anyway, as the sprag clutch was only a few thousand miles old I ordered a new gear 3 in case the boss was worn as you suggested. Once apart I really couldn't see any bad wear but slid on the new part anyway. Then there followed a period of head scratching and looking from different angles.

Robins sprag 1.jpg

 

After a cup of tea I realised there was a difference between the old and new part. The starter gear from the bike (Blue 04) has a bevelled edge. Right where the sprag connects. Where as the replacement (Yam) part from Totally TTRS had a squarer edge. So the sprag had only been in contact with about 2/3 of the boss. Plus was not sitting flat or square.

Looking again at the boss it is mostly worn just at the edge. I think that can be seen in the photo above.

Robins sprag 2.jpg


I hope that makes sense!

Am confident with the new starter gear (and new sprag), it will be sweet. I also noticed the starter motor splines looked pretty worn. Again only a few thousand miles wear, but perhaps the 'clunk' kicks back on the starter? perhaps upgrading to 'new style' starter gears fixes a couple of problems.

Have ordered a second starter gear to see if it is the same as the last. And to pre-empt on bike #2. Perhaps there were different batches made. Or perhaps Yamaha identified the problem and fixed it on later parts.

Anyway, hope that helps someone.

Cheers

Robin



__________________


Super Guru

Status: Offline
Posts: 6402
Date:
Permalink  
 

That does sound odd Robin!

I haven't got any Gear 3s out of an engine at the moment to have a look at but I can't understand why Mr Yamaha would have made them with a bevelled boss confuse

Maybe when fitting a new sprag, owners should check their boss and, if bevelled, order in a new Gear 3 - Steve keeps them in stock here.

Thank you for the research and letting us have the information!

Brian



__________________

Exeter, Devon, UK

http://www.ttr250.com  - The one and only dedicated TTR250 FAQ! 
 

http://ttr250.activeboard.com/ - THE forum for TTR250 owners



Super Guru

Status: Offline
Posts: 1151
Date:
Permalink  
 

I can confirm that the used Idler gears I have in stock all have a bevelled edge, approximately 2mm in length and maybe 0.3mm in depth

The new ones have a square edge.

Without opening a sprag clutch I am unable to see if the would run on the bevelled egde, but then why would they have changedconfuse

Robin are you able to tell if the sprag is running on the bevelled edge when fitted to the bike? Or maybe easier way to tell is if there is only wear evident on part of your sprag clutch's  teeth?

Steve



__________________

totallyttrs.com

 



Super Guru

Status: Offline
Posts: 6402
Date:
Permalink  
 

I think Robin has really hit on something here. I can't believe I have missed this apparent "flaw" over the years.

I have looked back over the photos in my sprag clutch folder and found a couple of photos that support Robin's theory.  See below where the sprag teeth are showing obvious signs of wear just on their outside edges evileye

I would appreciate thoughts from Mossproof and any other engineers or knowledgeable owners on here please!

I may have some re-writing of sprag articles to do disbelief 

Also, I hope you have a good supply of Gear 3s in Steve!!!! I may need one myself......

Sprag clutch 001.jpg



__________________

Exeter, Devon, UK

http://www.ttr250.com  - The one and only dedicated TTR250 FAQ! 
 

http://ttr250.activeboard.com/ - THE forum for TTR250 owners



Super Guru

Status: Offline
Posts: 1151
Date:
Permalink  
 

Think I will be ordering a few in the morning!

Lets hope this is the dreaded clunk causer, because if it is we have all had a result!

Don't think it is something you would have looked into Bri, Tiz only that the new ones are different that this has come to light.

 

Steve 



__________________

totallyttrs.com

 



Super Guru

Status: Offline
Posts: 1151
Date:
Permalink  
 

Oh and Robins diligencewink

 



__________________

totallyttrs.com

 



Senior Member

Status: Offline
Posts: 381
Date:
Permalink  
 

If the clunk goes away when you fit a new sprag clutch, then it is the sprag that is the problem, but if the teeth don't have contact across the whole width, then that would certainly accelerate the wear. Need some engineer's blue painted on the surface and fit the sprag on, then remove it and see how far on the teeth go. By the sound of it, Yamaha noticed the original part wasn't quite right and rectified it in the design of the replacement parts. More than likely not telling anyone about it in the hope that noone notices!
That's my take on it anyway
Cheers all,
Simon.


__________________
Page 1 of 1  sorted by
 
Quick Reply

Please log in to post quick replies.



Create your own FREE Forum
Report Abuse
Powered by ActiveBoard