Straighten Bent Crankshaft on Mower

[maradcliff]

Just wondering. I got a push mower with a bent crankshaft. The mower starts on one pull and runs great except it vibrates so bad that it's near impossible to hold it for more than a few minutes. I heard they have some sort of jig to straighten them, but also heard about doing it with a hammer and wood block. Is this really possible? If yes, where does one get a jig, or what is the method with the hammer? I dont need to get it 100% accurate, but right now it's beyond using as it is. It's just an old beater so I am not willing to buy a new crank unless I happen across a cheap used one. But if I can straighten it for a few bucks, I'll give it a try. The worse I can do is destroy it, and it's junk right now unless I get it straighter.

By the way, it's s 3.5hp Tecumseh

Mark

[Tony Hwang]

Hi, Think it's time for new mower if shaft is really bent.

[roger61611]

I don't know if this is the same thing but I had a push mower which I accidentally used to try to hone down a concrete thing that used to hold a basketball goal. The concrete thing won of course. This made the mower wobble like a washing machine filled with pennies. The rod that the blade attaches to was bent. Then someone stole the mower. I was glad, I don't how to fix that in a manner that would *not* lead to a repair bill that was higher than the value of the mower.

[m Ransley]

Have you tried a new blade

[Jeff]

Did that when I was a teenager. Hit a softball when cutting high grass. Just lay motor over, BE SURE to disconnect plug wire. Take off blade, figure out direction shaft is bent, the beat with hammer, be sure not to hit threads etc. Worse case buy a new mower.

[Italian]

As suggested below first I would try a new blade or balance the one you have if its not to far gone..if it still vibrates you know it is the shaft....

[e-mail] wrote:

[dpb]

All he has to do is check the runout w/ the blade off to verify it is the shaft.

If i has run any length of time that way the bearings quite possibly are also gone...

I Italian wrote:

[Maker of Rules]

Pick up a DVD of "The African Queen." Pay special attention to the part where Humphrey Bogart straightens out the bent drive shaft of the boat using nothing but a sledge hammer and a scrap-wood fire. Inspirational!!

[Robert Barr]

If you really like this mower, and it ran OK right up until the 'event', your best bet is to find a brand new short block. Google is your friend here. Compare its cost to that of a new mower with a warranty.

At best, your basketcase will run for a while before destroying itself. At worst, it will injure you when it happens.

[e-mail] wrote:

[Don Young]

Some mower shops have in-the-motor crankshaft straightening jigs even though no manufacturer recommends doing so. I have successfully straightened them using a long heavy pipe over the shaft and a heavy hammer. The last one was a 5HP Tecumseh which has been run hard for about three years since and is still going. The hardest part is holding the motor securely enough. You need some sort of indicator to tell how much and in what direction the bend is and how your straightening is coming along.

That is definitely not considered good practice as it is hard on the bearing and the shaft may crack, but it definitely is possible.

Don Young

[Stormin Mormon]

Could also very easily be a blade out of balance. Much easier to fix the blade.

[maradcliff]

OK, that's what I wanted to know. I will see what the local shops can do, or try it myself if too costly. If I wreck it, it's already junk the way it is anyhow. The shaft is definately bent. I can see it. It's VERY bent. The blade even chopped the tip off one of the bolts that hold the handle to the frame. It vibrates so much it creeps across the lawn by itself if I let go. My hands can not take the vibration for more than a few minutes. But I do like the mower. It's always been reliable and it's lightweight and simple, unlike most of the newer ones. So, if I do wreck it, I may check into a short block. And there are always used mowers too taht I can strip the engine block from.

I'd say the shaft is 1/4" off center, as I turn it.

[Andy Asberry]

Straightened or not, worse can happen. You do NOT want to try to avoid a spinning blade with a stub of crankshaft attached. You were correct when you said it was junk.

--Andy Asberry recommends NewsGuy--

[Goedjn]

You'd want to anneal it first, hammer it to shape, and then harden it again. If you know what your doing (which I don't) it shouldn't be hard. If you don't know what you're doing, then you'll have metal fatigue around the bend, which means (as another poster pointed out) that the shaft will shatter at some random time, at which point the blade will turn into a propeller, and chop you off at the ankles.