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

Members Login
Username 
 
Password 
    Remember Me  
Post Info TOPIC: Camshafts too tight?


Super Guru

Status: Offline
Posts: 8557
Date:
Camshafts too tight?
Permalink  
 


I have heard of at least three instances from owners where they had stripped and re-assembled their cylinder heads only to find that, when the camshaft journal caps had been torqued down, the camshafts were so tight they wouldn't turn. No obvious reason could be seen or found and the culprit is usually referred to as "galling" of the aluminium journals.

I have just had this issue and mentioned it to an engineering friend. As luck would have it, he had helped another TTR250 owner with exactly the same problem. 

To ease the camshafts he had made up a wooden tool as shown in the pics below. It is very basic and the procedure involves cutting strips of 600 grade wet and dry paper to slot into the end of the tool. Then, using a lot of WD40 as lubricant, the emery is placed in the journals and rotated back and forth until there is sufficient clearance for the camshafts to turn easily.

It is a very time consuming process and involves lots of checking to make absolutely sure only the minimum amount of "galling" is removed to allow the camshafts to rotate freely.

What's the alternative? As the camshaft caps are line bored in situ, the head and caps are only available together at a massive £955 retail d

I am passing this on for information and cannot recommend any other owner to do the same!

Brian

Camjournaltool1_zps1bab0aec.jpg

Camjournaltool2_zpsa0539351.jpg

Camjournaltool3_zpsc3953a91.jpg



__________________

Exeter, Devon, UK

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

TIP: For easy viewing bookmark the "Recent Posts" view - http://ttr250.activeboard.com/p/recent/ 



Veteran Member

Status: Offline
Posts: 85
Date:
Permalink  
 

Very interesting Brian,thanks for the heads up.
I could see why that fix would be a long job, just hope I never find out how long.

__________________
Lin


Senior Member

Status: Offline
Posts: 129
Date:
Permalink  
 

Any theories as to why the camshaft bearing clearances close up? Residual stresses deforming the head? Wrongly torqued head bolts?

__________________


Super Guru

Status: Offline
Posts: 8557
Date:
Permalink  
 

Lin wrote:

Any theories as to why the camshaft bearing clearances close up? Residual stresses deforming the head? Wrongly torqued head bolts?


Hi Lin.

I was chatting again to my engineer friend and I think we have agreed that there must be some movement in the cylinder head casting when it is removed from the engine.   

It doesn't need to be much to make the camshafts bind. We can't think of what else it can be. 

Brian



__________________

Exeter, Devon, UK

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

TIP: For easy viewing bookmark the "Recent Posts" view - http://ttr250.activeboard.com/p/recent/ 

Lin


Senior Member

Status: Offline
Posts: 129
Date:
Permalink  
 

In general cyl head bolts should be loosened in stages and in the reverse order of tightening.  As well, the engine should be dead cold, especially aluminium ones.  I could envisage some head distortion if the above is not observed.  

 



__________________
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