A tale of two Chouts

The Ultimate Indian Motocycle Hybrid, the marriage of a vintage Scout frame with a Chief engine!

The Alchemist

The essence of motocycle, picture a rigid framed vintage roadracer, leaf sprung fork, single pan saddle, hand gearchange, foot clutch, left hand throttle and the biggest production Indian engine of the time shoehorned into the best handling Indian frame of All time! A true hotrod, the looks of a stripped down wall bike on steroids!

Thursday, 23 December 2010

Valve spring study

After a trial fit of the Shunk cams, bonneville followers and the cylinders fitted with standard spec valves and springs it was noted that the springs were binding just before full lift. With the Chief std spring fitted I measured fitted length, with it removed and fitted in a vice I measured free length then fully compressed to coil bound.
Std Chief  - free length = 65.65mm
                 -fitted length = 45.10mm
                 - coil bound = 36.71mm

with the Shunk cam and bonne followers the lift is 10.91mm so its easy to see that there woulnt be sufficient free movement in the spring.

I pulled a set of used 741b springs from my spares pile and checked them out.

used 741b - free length = 59.58mm
                 - fitted length = 45.10mm
                 - coil bound = 31.05mm

a full 5.66mm of extra spring movement. referring to Jim Mosher's valve spring study the spring pressure of the shorter Scout spring is similar to the Chief one throughout the movement range, so it seems that 741b springs will be suitable to use on the Chief motor with the hi lift cams and bonne followers.


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