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I guess that's the end of that! The 20" Murray push mower a mowing client gave me has a bent shaft. I was fearful of that since it had this weird pull of the rope, like it was "catching on something" and the shaft itself (with blade removed) was very wet with oil. The blade itself looked really good though: no damage, only rust.

With blade off though, it's clear the shaft is not sitting in the center of the shaft tunnel.

I now know what to check first when someone gives me a mower!

I'll continue cleaning up the carb and gas tank...........I already have those off anyway.

Anyone have a good shaft laying around they don't want?

engine model?
Ebay can be your friend for used cranks....

A few decades days ago I knew a guy whose main business was straightening bent mower crankshafts. I don't know how he did it.

My dad told me of a shop that straightened mower cranks without removing those from the engine.

I doubt anyone does that now.

The local landfill sells lawn mowers for $5.00. I might start checking there.

Ring around a few local repair shops.
Because you lot only use bar blades a lot of cranks get bent and B & S makes a crank straitener

Scrubcadet10 said:

engine model?
Ebay can be your friend for used cranks....

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Engine model number: 9L902

How old is that you think?

*Nothing on ebay when searching that model number. Did find it on repairclinic.com for just over $100.00.

796211 https://www.ebay.com/sch/i.html?_fr...esc=0&_odkw=Briggs+3.5hp+crankshaft&_osacat=0
shows, 2 cranks, but the old number was superceded to this number....
post the Date code of the engine, it's the longer series of numbers 9L902-xx-xxxxxxx

OK, let me do that.

9L902-0221 E1 04062952

There is a tool for straightening cranks in the engine. I have one but haven't uaed it in years. Some folks use a hammer but i have never tried that method.

Hammermechanicman said:

There is a tool for straightening cranks in the engine. I have one but haven't uaed it in years. Some folks use a hammer but i have never tried that method.

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Where do you live? I can come to you and pay you for your time or bring whatever food/drinks you prefer.

Southwest Ohio. Long drive from WV if that where you are.

Hammermechanicman said:

Southwest Ohio. Long drive from WV if that where you are.

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That's not a long drive at all. I used to drive 3 hours, one-way, for literally 60 seconds of fun back when I was skydiving every other weekend.

I have driven 19 hours one-way just to ski for two days. (Hopefully will again this coming ski season).

Longest trip was 13,000 miles one-way to see my girlfriend (I didn't drive that one though....car doesn't float).

If you are game to try, I'm game to come. What's your favorite beverage?

I have a crankshaft straighter too. They work very good. Uses a dial indicator and you get them perfect to within a few thousands. Haven't used in years as most all newer engines have very short cranks and rarely bend.
And you do them right in the motor without anything apart other than taking the motor off the deck..

Sometimes you got to kiss em good by and just get a new one.

You have nothing to lose here drain the oil put the mower onit's side and careful hit the shaft high spot with a sludge hammer until you get the shaft as straight as possible. Take your time and then put the blade back on and check your work, don't be afraid of hitting it hard, I did this with one a "friend" gave me it is still running today 2 years later..... You have nothing to lose..... ps From what you describe MAKE sure the shaft is indeed bent I suspect you might just have a broken keyway ..... check this anyway even if the shaft is bent since this will cause the engine to be out of time and pull the cord right out of our hand.

Use a Dial Indicator and mark High Side. A piece of pipe over the end of the protected shaft and lean on it.
Check runout often and remember 'spring back'. Replace the seal if you get it 'good enough'.

I straightened one using the big hammer method, I could cut grass with it, but it still had enough vibration that I had to tighten the carb bolts every couple weeks. Go down to Lowes and buy you a cheap Bolens 20".

MowManWV said:

I guess that's the end of that! The 20" Murray push mower a mowing client gave me has a bent shaft. I was fearful of that since it had this weird pull of the rope, like it was "catching on something" and the shaft itself (with blade removed) was very wet with oil. The blade itself looked really good though: no damage, only rust.

With blade off though, it's clear the shaft is not sitting in the center of the shaft tunnel.

I now know what to check first when someone gives me a mower!

I'll continue cleaning up the carb and gas tank...........I already have those off anyway.

Anyone have a good shaft laying around they don't want?

Click to expand...

If the symptom is the mower seems like it wants to pull the rope out of your hand when you pull it then the flywheel key has sheered.
Remove the flywheel nut and you can usually see if the keyway aligns with the key.
This happens because with a sheered key the mower is "out of time" and depends on how bad the crank is out of alignment with the flywheel the mower will fire the piston backwards as it is not sparking at TDC.

Check If the blade is hitting the deck also.

replace the key and tighten the flywheel back on.

Alot of the time when mowers come into my shop with this issue, you replace the key, then start it and the mower will vibrate when it's running.
This is a bent crankshaft, a badly bent crankshaft and the mower will walk around in circles if left to run on concrete.

If it's not too bad mow with it,. eventually you'll tear it up, or replace the crank or have a shop bend it back.
Most shops won't straighten cranks though, special press/tool to do so,.

mabel said:

If the symptom is the mower seems like it wants to pull the rope out of your hand when you pull it then the flywheel key has sheered.
Remove the flywheel nut and you can usually see if the keyway aligns with the key.
This happens because with a sheered key the mower is "out of time" and depends on how bad the crank is out of alignment with the flywheel the mower will fire the piston backwards as it is not sparking at TDC.

Check If the blade is hitting the deck also.

replace the key and tighten the flywheel back on.

Alot of the time when mowers come into my shop with this issue, you replace the key, then start it and the mower will vibrate when it's running.
This is a bent crankshaft, a badly bent crankshaft and the mower will walk around in circles if left to run on concrete.

If it's not too bad mow with it,. eventually you'll tear it up, or replace the crank or have a shop bend it back.
Most shops won't straighten cranks though, special press/tool to do so,.

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Guys, I like to fix things, which is why I am here and not reading reviews on Lowe's.com .......I enjoy the challenge and opportunity to learn something new. *I'm not hurting for a mower, I have a backup I got running last week and my main mower may be fine after a carb cleaning or rebuild.

So remove the flywheel and check the flywheel key?

Blade didn't appear to hit the deck (blade is off right now) but shaft where blade attaches to it is clearly moved to one side. It has an oblong rotation when the flywheel is spun fast with a drill.

I agree with the sledge hammer trick. Worked for me.

MowManWV said:

Guys, I like to fix things, which is why I am here and not reading reviews on Lowe's.com .......I enjoy the challenge and opportunity to learn something new.

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Good for you. It's easier and often cheaper in the short run to replace a thing or have someone else fix it, but if you never fix anything you will never learn anything and you will always be helpless and getting ripped off.

MowManWV said:

So remove the flywheel and check the flywheel key?

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If the crank got bent, the flywheel key will usually be sheared. If it's not, most likely some idiot replaced it with a piece of hard steel or even JB Welded the flywheel on. If that's the case, you sure want to know it now.

Rich,

Thanks man. Frankly I'm a little surprised a lawn mower forum has members that suggest buying a new mower over fixing it. I thought the purpose for a forum was to help others fix stuff.

Got the mower for free.....enjoy the challenge.

Now that the remnants of Hurricane Ida blew through I have several yards to mow but after that I might try to dig into it. I'll remove the flywheel next and see what that key looks like.

If no member steps up with a shaft straightener, I will contact repair shops and see what they have to offer.

May gear up for a rebuild.

MowManWV said:

Rich,

Thanks man. Frankly I'm a little surprised a lawn mower forum has members that suggest buying a new mower over fixing it. I thought the purpose for a forum was to help others fix stuff.

Got the mower for free.....enjoy the challenge.

Now that the remnants of Hurricane Ida blew through I have several yards to mow but after that I might try to dig into it. I'll remove the flywheel next and see what that key looks like.

If no member steps up with a shaft straightener, I will contact repair shops and see what they have to offer.

May gear up for a rebuild.

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Because crankshaft straightening was very common, you can create stress fractures in the metal from fatigue that could later break and cause property damage and ;personal injury, and so it is recommended to just replace the crankshaft or replace the mower because people especially technicians and repair shops don't like getting sued for potentially millions of dollars.

I'd still straighten the thing. If it cuts off my leg, that's on me.
I'll sign any release anyone wants when it comes to that or any other risk I take.

But even with the signed release the shop could still be liable if your crankshaft breaks and the blade cuts off your neighbors leg.

My liability insurance had to pay a claim a few years ago because a guy was cutting a tree down and when he pulled the saw out of the cut the chain came off and cut his fathers leg requiring 46 stitches that was standing next to him. My only liability was that I had handled the saw last before the accident. No fault was found on my part but they paid the claim as a no fault claim.

ILENGINE said:

But even with the signed release the shop could still be liable if your crankshaft breaks and the blade cuts off your neighbors leg.

My liability insurance had to pay a claim a few years ago because a guy was cutting a tree down and when he pulled the saw out of the cut the chain came off and cut his fathers leg requiring 46 stitches that was standing next to him. My only liability was that I had handled the saw last before the accident. No fault was found on my part but they paid the claim as a no fault claim.

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Holy aping ass monkey!!!! I'll be more careful about chain tension.

Crankshafts used to get straightened all the time, and I've used mowers with straightened cranks (have a suspicion I'm using one now). I never heard of one breaking, and I don't doubt one straightening is okay. But if it's been straightened before... how do you know? How many times? Could be a mess when that blade hits a stump.

Richard Milhous said:

Holy aping ass monkey!!!! I'll be more careful about chain tension.

Crankshafts used to get straightened all the time, and I've used mowers with straightened cranks (have a suspicion I'm using one now). I never heard of one breaking, and I don't doubt one straightening is okay. But if it's been straightened before... how do you know? How many times? Could be a mess when that blade hits a stump.

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Actually in this case it wasn't related to chain tension. The problem was a 20 inch narrow safety bar that allowed enough side flex to derail the chain if side pressure was exerted on the rear handle when felling. People tend to either push down on the rear handle or pull up on the handle when felling a tree. In this case while testing with an identical saw that caused the accident, I could put the nose of the bar on a chuck of wood and while holding the rear of the handle up with one finger could flex the bar about 1 to 1-1/2 inch just from the weight of the saw pressing down on the bar.

Worked on another saw years ago that the customer was complaining his new chain wouldn't cut straight. With that saw and a similar bar as the accident saw I could make it cut straight cuts with just normal rear handle pressure, but If I pulled up on the rear handle with extra force could flex the bar to make it cut crooked.

And I have seen two crankshafts shear off after being straightened. Don't know all the details behind them so could of been multiple straightens or something else at work.

I never put blame on anyone else if I can possibly put it on myself. If you'd like impressive examples of this, drop me a PM.

Bring on the shaft straightener!

Found this video.....

Shaft straightening