On Sun, 12 Apr 2009 20:54:49 +0100, Jules13 wrote:


Hi, hoping someone can help me to establish whether I really have
knackered my girlfriends expensive lawnmower !!

its a Briggs & Stratton Sprint 40, which I'm fairly sure is 4 stroke

There's all sorts of prelude to this, but suffice to say that the
lawnmower is new-ish, was recently serviced and running fine til this
incident.

I turned the mower on its left side, so that the spinning blade was
visible, not noticing at the time that this was the side of the exhaust
outlet. It ran normally for a while, but then billowed white smoke from
the exhaust.

The gap between the exhaust and its guard may or may not have allowed
sufficient room for escape of gases. I know for a moment i had a very
small fire on the lawn there.

Also a reasonable quantity of engine oil had obviously been expelled
from the exhaust. I believe that oil out of the exhaust is very
serious indeed.

It sounded normal til it cut out and did restart once, the smoke
beginning to die off til it cut again after about 30seconds and it will
now not restart.

I fear that perhaps the engine was starved of oil; perhaps the pick up
is on the side of the sump that gravity had taken the oil away from?
Would I normally have heard knocking from the main bearings if that was
the case though? And would it more likely have seized? (its not
seized)

Or might the constriction to the exhaust have burnt out an exhaust
valve?

I used to dabble in mechanics to cars, most ambitiously on one occasion
completing a head gasket job (after much trial and error).
How simple are these engines?
What is it the most likely problem with it from the above?
Is it a foregone conclusion that the only realistic thing to do is bin
the mower?

The spark plug is clean by the way, and the engine turns over and fires
normally on a pull, without starting.

Advice much appreciated

Thank You

Fires normally on a pull without starting ??? I'm not a lawn mower mechanic, but
couple of usual things....

You turned it on the side....while running... that's a heck of a dumb thing to do, but
you already know that.

Oil would have passed the rings... gone into the cylinder... that's the smoke you saw
coming out of the exhaust. You might have run out of fuel or created vapor lock in
the fuel system....

Couple or two things you could try...

Make sure you have sufficient oil in the sump

If you have a spark tester... check for spark. If you
don't have a spark tester, you might wish to try an insulated tool
to hold the cable about 1/4 inch from the plug... This might take
two people... one to hold the cable, the other to pull the rope.
Do NOT ground yourself in ANY way to the mower while trying this. You'll know
soon enough if you have spark.

Turn it over a few times with the spark plug out.
Place finger over hole while turning over.... you should feel
a moderate amount of compression, If your finger is covered
with oil, you probably would want to turn it over a few time
to clean the oil out.

Removing air filter... try spraying engine start, or even a little gas
into the carb.. choke open while spraying, close choke. Try to
start.

A seized engine will not rope start easily... Bearing knocks are
pretty obvious IF it starts. You might just have too much oil
in the upper cylinder preventing it from starting.... or you might
have burned a valve.

A lot of engines have a grounding switch which prevents engine
from starting when safety handle is not depressed. You might
have knocked off the spring... so the grounding switch is not released.

Just a few of the things you could try...before discarding the mower....

Peter