Geoff Griffiths wrote:
Thanks for the replies folks.

"try new IIRC at 3600 rpm it doesn't take much out of balance to
rattle"

can you please explain what the above means (IIRC)?

It stands for "If I recall Correctly" and the statement is nonsense.


I have tried to watch the blade retaining nut whilst trying to pull the
cord but it's really difficult. I also turned the blade by hand but
couldn't detect any non-concentric movement.

It's usually a bolt. At least here in the US. Not sure what the norm is
in the UK. Removing the spark plug so the engine will spin freely and
smoothly is a critical step. Otherwise it bounces around and is
impossible to see a wobble.


Would running the mower without a blade attached show if it's the blade
causing the problems?

Not a good idea. Most mowers use the blade as a flywheel and won't run
without the blade attached.


I have noticed it makes quite a loud 'clunking-type rattle' just as the
engine stops - any more thoughts please?




That clunking sound means the blade is loose. Remove it and the adapter
and examine for anything sheared or broken. Replace as needed and
tighten it up.

--
Art