I remember reading somewhere in this ng where somebody straighted a
LawnBoy crank themself. Could someone respond, hopefully the guy who
accomplished this feat, and tell me how to? I could buy a new
crankshaft for this thing, but at $145.00 i want to give it a try with
my tools, I mean what have I got to lose?
Total deflection at the tip of the shaft [lower tip] =1/16". Not too
much deflection near the lower seal.
What should I do? Reassemble with new seals and say my prayers? Or,
try to straighten the crankshaft?
Bent crankshaft in a lawn mower engine?
As far as I am concerned it is junk! No manufacturer recommends
straightening crankshafts for good reason. Most mower crankshafts are cast
iron, once bent, they crack. Straighten them and they crack more!
Now all that said there will be 100 other posters that will tell you the
opposite. I did small engine repair for 5 years and ALL small engine
manufacturers said not to straighten cranks.
A while back someone here claimed that Briggs & Stratton sold crank
straighten tools. I asked for part numbers for the tools, and the poster was
never heard from again! there is some aftermarket companies selling
straightening tools, but no engine manufacturers!
It is a lawn mower with a sharp blade attached, spinning at 3200 RPM. What
is your leg worth? What is your leg worth after the crank breaks and sends
the blade through it?
As far as just running it, 1/16" of an inch of run out is allot when it is
turning at 3200 RPM. It will vibrate like a S.O.B.!!
I found a good used crankshaft, sent to me via email from a guy in PA
who found a terribly neglected lawn boy in the trash. he knew my
story, picked up the mower, and basically charged me shipping to get
it to me with all the remains of the mower engine still attached. I
just about had tears when he told me he would ship it to me just for
the cost of shipping.
Anyway, it was completely covered in moist greasy dirty oil and then i
opened it up i found more black soot than kris kringle ever saw, but
the metal parts of the piston and cylinder were solid, no scratches,
they nearly looked brand new after the cleaning i gave it. So now the
motor is assembled and on the deck, I still need to put on the little
things like tank and muffler, etc. I finally took the piston out of
my old mower and it looked like a cheese grater with all the pitting
and scorching on it, i could hardly beleive it even ran like that.
Thanks guys for all the advice, etc. Mission accomplished.
Good for you!
I used to cobble mowers together from random "junk".
You lucked out finding a similar model so parts were the same. Lawn Boy was
good for that. Many different models, but very few different engines over
My first mower was built from two junkers, I believe it is the one my
neighbor is using now. It was 15 years ago when I cobbled that one together
and it still runs great.
I dont know a machinist, would a machinist do this as a service, or do
you have to 'know somebody'? i dont have any of these types of tools,
but do you think it is safe to use a mower with a repaired crankshaft?
I just read some information that says it might be dangerous because
of small cracks in the shaft after the straightening. I dunno.
Junk it, don't bother. Cast iron is brittle. It can be broken with a
few whacks of a hammer. Even if you could bend it back straight, it
would most likey crack, if it isn't already. It will work for awile,
then catostrophically fail - perhaps embedding the blade in your leg in
I do nondestructive testing for a living, which means I'm paid to find
material defects such as cracks. I have seen what can happen when
somethng fails, and let me tell ya, it ain't pretty! Be safe and don't
do it. It's not worth the risk!
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