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?
THanks, Fish
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?
THanks again, Fish.
Do you know a machinist in the area? The way I do them is with a small hydraulic press, two v-blocks and a dial indicator. This really isn't something you can eyeball.
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.
Fish.
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.!! Greg
I agree, I read that some where you shouldnt straighten them. Thanks. I found a crank on ebay thats used, but still straight.
Fish
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 the process.
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!
Joe Michel
=1/16". Not too
prayers? Or,
recommends
crankshafts are cast
crack more!
will tell you the
small engine
sold crank
and the poster was
companies selling
at 3200 RPM. What
breaks and sends
allot when it is
them. Thanks.
It probably makes more sense to just find a used mower with other problems and swap parts.
Bob
UPDATE
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. Fish.
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 the years. 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. Greg
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