On Sun, 22 May 2005 15:40:59 +0100, "Peter Coddington"
wrote:

I have a Qualcast Suffolk Punch petrol mower (43S,Model, 17 inch cut)
Cutting the lawn the blades suddenly stopped revolving and the engine became
louder. Nothing caught in the blades. Clutch adjustment seems OK,Looking at
the drive chain this adjustment is as it should be but with the engine
running the top pulley is not revolving so therefore it is not turning the
bottom pulley to drive the blades.
With the engine turned off I can turn the chain by hand and both pulleys
revolve.
The nut securing the pulley is tight so it seems that the shaft on which the
pulley is attached has come adrift somewhere.
Not being a mechanic is seems to be an expensive engine strip down job? Any
views please.?
Peter.

If I remember rightly the pulley is keyed on to the shaft on these
machines. It's a semi-circular key which fits into a slot on the
shaft and corresponding slot on the pulley, preventing it from turning
on the shaft (or the shaft turning without the pulley). It may have
sheared off - it's a fail safe in case the blades are seriously
obstructed as can happen if a stone gets between the cylinder and the
bottom blade. I'm not certain about this but it's probably worth
removing the pulley (you'll have to stop the engine from turning as
you unscrew the nut) and having a look. It shouldn't need a complete
engine stripdown. Another point - is there a disengageable dog clutch
between the engine and the top pulley? If so, is everything OK there?
Dredging my memory again, some of the Suffolks had a centrifugal
clutch which engages the drive as the engine speeds up, like on a
moped. If the friction material on the clutch shoes wears out or gets
contaminated with oil nothing moves!