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The TTR250 FAQ web pages -> TTR250 -> Repair and maintenance "stickies" -> Camshafts too tight?
Post Info TOPIC: Camshafts too tight?
TTRfan


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Camshafts too tight?
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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



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Andy_C


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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.

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Lin


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

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TTRfan


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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



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Lin


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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.  

 



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