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Clutching at straws
Posted by : Neil (92.26.211.144) 
Inappropriate or SPAM?
On Thursday 25/08/16 at 01:21:07
In my experience, semi auto primary clutches, begin to struggle to grip when you get above 110cc. Certainly Scruffs brand new Lifan 125 clutch slipped as soon as I fitted a 142cc big bore kit all those years ago. So with this in mind, I knew the standard Lifan 125 clutch was not going to cope with the YX140 top end.
Through trial and error...a lot of trial and error, I have built semi auto clutches that grip perfectly on even tuned 140’s, one such clutch is in Scruffs current engine and the other in my Chinese Chaly clone called Big Mig. Big Mig is a mildly tuned 113cc, but it still slipped every standard clutch I fitted to it even with new plates.
When building a heavy duty clutch I start with a Lifan 125 clutch which has extra weights in it. The problem with the extra weights is they simply compress the standard springs so you don’t get the full benefit of the extra force created. To prevent this I add a single washer under each pressure spring. Two washers is too much and the clutch can’t be released. I also fit a TB heavy duty clutch plate set, which are thinner than standard plates, which allows them to fit an extra plate in. Once all this is done, I then spend countless hours fettling to prevent the clutch from dragging at tickover, it separates properly when trying to change gear going downhill with the throttle shut, and still doesn’t slip on either the kick-start or when riding under load.
So given all this, I was not keen to be building another one of these clutches. So I have taken the decision to pinch the clutch from Big Mig and replace it with the brand new Lifan 125 clutch which was on the bottom end I used for this engine build. Hopefully Big Migs 113cc engine won’t slip the Lifan 125 clutch.
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