Straightening crank shaft on push mower

Have any of you ever straightitend crank shaft before because I was at the junk yard yesterday and saw a nice Honda mower with a bent crank shaft if you can do this I will get it

Ean said:

Have any of you ever straightitend crank shaft before because I was at the junk yard yesterday and saw a nice Honda mower with a bent crank shaft if you can do this I will get it

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I'm going to say pass on it if you plan to try to straighten the shaft. I've heard it can be done but I wouldn't bet on it. That's like trying to straighten the crank shaft on your car. Not a good idea at all.
If it's good otherwise and dirt cheap then a new shaft and bearings would be a good project. I wouldn't do it... but I could get one in good shape for less than the parts would cost to fix that one.
Good running Hondas are plentiful around here.

Ean said:

Have any of you ever straightitend crank shaft before because I was at the junk yard yesterday and saw a nice Honda mower with a bent crank shaft if you can do this I will get it

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I know this sounds ludicrous and if I had not seen it happen I would not believe it either. However.

One time my grandfather bought a push mower with a 3.5 Briggs on it. He did not run a tank of gas through it before he hit a steel rod in the ground and bent the crankshaft on it. He then put it in the shed and bought a new one. This one was bent so bad it was locked up.

A couple of years later I needed a push mower to cut my small yard in a trailer park lot. I got it out and decided that I would try to find another mower and get a crankshaft out of it and put in that motor. I had to get the adapter off of the bottom of the motor to get it off of the deck. I did not have a puller. I loaded it on the truck and carried it to a small machine shop up the road from my house to see if I could get the old guy there to pull it off for me. When I got there and told him what I needed he looked at the mower and said, "That mower looks like new, why don't you just straighten it out"?

I told him that I did not know it could be done. He said he had done it before. We took it off of the truck, turned it up on it's side. He gave me an ax and told me to hold it up against the bottom of the shaft away from the direction the shaft was bent. He then took a 4# hammer and hit it on the opposite side. He did that several licks. All of a sudden when he hit it the shaft started to turn.

Then he would turn it to where the bend was up. The I would put the ax under it and he would hit it. He did this several times till it only had a wobble on it.

He then took a piece of soap stone and held it close to the shaft and instructed me to turn the shaft. I did it slowly and he moved the soapstone closer till it marked the shaft on the high spot. Then he would take the shaft and turn the spot with the soapstone mark on it to the top and had me hold the ax under it and he would tap it. Then he wiped the soapstone off and we turned it through checking again and then hit it again on the high spot with me backing it up with the ax.

After a few times of this he had it tried enough that you could not see a wiggle on it and there was little if any run out in the shaft. We then put the blade on it, put gas on it and started it up.

I ran it for several years.

He said that the purpose of backing it up with the ax was to keep from busting the bottom of the motor.

He also said it was bent it the throw of the shaft.

Straightening a shaft is part art form, and best left to a machinist who will have to charge for his time. Make the cost tradeoff . If you are curious about the technique go to youtube after search word "straighten shaft." You will see a setup of V blocks , indicator resting on the shaft, and some means of hydraulic force . The operator slowly pushes the high side past zero runout, waits for the shaft to spring back and repeats. Although blows from a hammer will move the shaft around I would not recommend it unless the mower is free and you are curious.:thumbsup:

edit: change axe to hammer

once steel is bent it changes properties (becomes weaker),after its straightened it needs magnafluxed in turn if any cracks show up,you just waisted money and time.

Straighten it with a big hammer. Take that advice or leave it could care less.

Again, what is a "nice Honda mower" worth? A good (can you find one?) machinist would probably charge $50-$100 for the straightening. Mag inspection another $25. If is fails it's trash time. Expensive auto heads can be straightened (part art, specialty shops). Afterwards they are heat treated. Such heads are $5K new. Apples and oranges.

Here is a couple of pics of my old one. It didn't really straighten, but merely re-bends the crank so that it cuts even and doesn't vibrate, works great!!! Sorry, I don't have an engine handy to mount on there, but it is pretty straightforward.

Way to go fish!

motoman said:

Again, what is a "nice Honda mower" worth? A good (can you find one?) machinist would probably charge $50-$100 for the straightening. Mag inspection another $25. If is fails it's trash time. Expensive auto heads can be straightened (part art, specialty shops). Afterwards they are heat treated. Such heads are $5K new. Apples and oranges.

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Sure the kid is going to spend over a 100 + dollars to straighten a crankshaft after he takes the engine completely apart and puts it back together. Big hammer. I have done it and you will be surprised how close you can get it. Time he spends that kind of money and time he can buy a good used mower. Then on top of that I don't know what junk yard or salvage yard will sell a complete mower. They sell parts. But also I don't know his salvage yard so maybe??