Any one ever fix a slightly bent crank shaft on a lawn mower. I am thinking heat and a dial indicator. Could this ever work on a new Honda motor? I got the mower for free today.
Any one ever fix a slightly bent crank shaft on a lawn mower. I am thinking heat and a dial indicator. Could this ever work on a new Honda motor? I got the mower for free today.
My opinion is that heat is a bad idea. Hydraulic press and dial indicator. Be a shame to toss a new Honda motor. How far out is it? I've done that hitting an iron pipe, mower shook like crazy afterwards. It was an old clunker, just scrapped it after that.
Never done a crankshaft, but I have precisely straitened other shafts with hydraulics though. Go slow, use the dial indicator, and check often. Also - if there is twist it will be much harder than if there is a simple bend.
i've seen a kart axle straitened with a couple good whacks of a deadblow. they didn't even pull it out of the chassis, just pulled the hub off and gave it a couple whacks and it was back like new. the steel wants to go back to its original shape, it just needs some "massaging"
I've done this successfully.
You'll need:
I removed the blade, spark plug, gas and oil and attached the mower to a couple 8' pressure treated 4x4s I had handy using ratchet tie-downs. I rotated the crank and using the dial indicator located the plane in which the crank was bent and marked it with a Sharpie.
(Note: nearly every interesting project involves a ratchet tie-down and a Sharpie)
My force multiplication device was a 4' length of 2" square steel tube with pretty thick walls. I happened to have a length of round tube that was an acceptable fit over the crank stub and in the square tube.
Check the runout (and mark where on the stub you're checking it, for repeatibility) slide the cheater bar on and give it a little heave. Not too much!
Check runout, repeat as necessary.
Mine straightened out just fine. It's the stub that bends, not the middle.
I fixed a bent S-10 axle like this many years ago. It probably wasn't as straight as your crank needs to be. We used a lathe and dial indicator to gauge our progress (measured at the bearing surface), then turned the wheel mounting surface to true the wheel.
An old fellow who used to live in my neighborhood ran a small engine repair shop out of his garage; no advertising, just word of mouth. He had as much business as he could do, and then some.
He'd been working on power mowers since their invention, I think.. I mean, this guy was in his 70s.. knew a B&S engine like the back of his hand. He built a wooden jig for straightening bent cranks, had it mounted to a sturdy workbench. he would take the engine apart, and set the crank in his grassroots jig, turn it until he determined the direction of the bend. Once it was set, he would reach for his BFH (about a 3# drilling hammer), and rear back and give the crank one good whack. Worked every time.
I had another friend in the small engine repair business, who saw this, and tried to replicate the jig, but never got it to work well.
The old fellow is no longer with us. Many would say breaking an engine all the way down to straighten a crank would be too much trouble, and take too much time, but this old guy could tear one down, knock hell out of it, and put it back together in less than an hour. IIRC, he charged about 40 bucks for the job! 
A professor of mine has done this with small engines. Like others have said, he used a lathe and a dial indicator with the crankshaft removed, but if its just the pto that sticks out of the motor thats bent, I don't see why you'd need to tear the whole engine down.
Jamesc2123 wrote: ... I don't see why you'd need to tear the whole engine down.
I thought it was overkill as well, but this guy had been working on engines longer than I'd been alive, so I never questioned his methods.
Wow thanks for all the great ideas. I knew you guys could help. I will play with it this weekend and post my results.
Thanks
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