"Art" wrote in message
...
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

Some of the B&S engines have a bag of spanners inside, just under the debris
cover. Well, actually it's some little steel balls that act as a sort of
cintrifugal clutch in case you should hit a big root. Maybe your balls are
stuck. Simply cleaning them and perhaps a little spray lube such as WD-40
should get them working again. Like Art said, don't run it without the
blade. It's part of the whole.

I have an old (23 years) B&S 3.5 HP mower and I've hit concrete curbs and
other horrible stuff with it and it has never even sheared the flywheel key.
It always turned out to be the little steel balls (plus replacing mangled
blades). After removing the debris cover (assuming this model is the same
as mine) there will be a nut/bolt in the middle on the top. Remove that.
When you lift the shaft it will misalign the steel balls from the mechanism
and it can be a bit tricky to get them back in the right place. The are a
bit like washing machine agitator dogs.