Bent crankshaft on a new Briggs 5.5hp engine.........repairable?

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I acquired a 3 week old "Yard King" self propelled lawnmower with a Briggs 5.5hp Quantum engine from a neighbor. She said she just bought it and hit a tree stump and it started vibrating. I put it on its side and can definatley see a slight wobble. It starts and runs with a slight vibration, and tends to want to slide to the right when I'm holding it still on concrete. Is it possible to "fix" the crankshaft? How hard is it to get the crank out on these engines? Is it worth it? I beleive a new crank is about $50.00. Any thoughts?
 
It bent, so it can unbend without disasembly. Take a 10 lb sledgehammer and hit the high side. Work up in force until it bends back. With practice you can get them quite straight. I have probably fixed 20 or so to make money in college. Yes I did kill a few. First one I fixed. Then I killed one. Rod
 
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Originally Posted by ragtoplvr
It bent, so it can unbend without disasembly. Take a 10 lb sledgehammer and hit the high side. Work up in force until it bends back. With practice you can get them quite straight. I have probably fixed 20 or so to make money in college. Yes I did kill a few. First one I fixed. Then I killed one. Rod


This. It's already broken and not worth rebuilding so you might as well try. I've done it with my 5.5hp one several years ago and it still runs fine. Maybe it shortened its life, maybe not, but it was either that or chunk it.
 
Don't hit it with a sledge hammer, you will likely break the aluminum oil pan. The only way to straighten it without risking breaking the oil pan is to use a crankshaft straightener, but for a one time use, it is far too expensive (over $300 new). I had one in my shop that I used quite often, but never as a straightening service that I sold, only to straighten a crankshaft so that I could get the oil pan off to replace it. If you are lucky enough to have an engine where the lower bearing journal is a larger diameter than the external part of the crankshaft, you don't have to straighten it to get the pan off. Replacing the crankshaft is not that difficult if your mechanical aptitude is good. You don't even have to remove the head to do the repair. In addition to the crankshaft, you will need to buy a pan gasket, a lower seal, and a flywheel key.
Lawnmower crankshafts are made of cast iron which is brittle, it should never be straightened and put back into service. When you hit something hard enough they bend, but they also twist and get microscopic fatigue fractures which makes them weak and can cause them to break during use. In our dealer agreements, the major engine manufacturers would not allow us to straighten crankshafts.
 
Originally Posted by ragtoplvr
It bent, so it can unbend without disasembly. Take a 10 lb sledgehammer and hit the high side. Work up in force until it bends back. With practice you can get them quite straight. I have probably fixed 20 or so to make money in college. Yes I did kill a few. First one I fixed. Then I killed one. Rod

This is nonsense. You will never safely straighten a crank doing this hit or miss method. You will likely destroy it.Toss it like your neighbor did. It may have a bent blade too.
 
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Originally Posted by JetStar
Since the original post was 16 years ago, it's probably too late to offer advice.

Agree but thought it could benefit someone getting the wrong idea.
 
sorry for some reason I must have inverted the order and read an old post.The old briggs of 40 years ago, I could save 3 out of 4 with out problem. I mowed a lot of yards, the clean ones I used a lawnboy (1979) that I still have, bet it has over 2000 hours on it, third set of wheels, no count on blades, the rear wheel bracket I had to drill out and replace rivets, and put a spacer where the height adjust bar had worn almost its full width was in the deck and one overhaul, with all new bearings, seals rings and piston.

briggs I used for the dirty yards, and dog pens. (you do not want an underdeck muffler mowing dog pens) I never had a straightened crank break. I would get 100 or maybe more hours out of the used ones, then scrap them and use another bought for $10 or 15. I would also fix and sell for 40 buck, some of the nice self propelled ones got 60., Cheap mowing. This was over 40 years ago, so your MMV vary now.
 
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I've pounded the shafts straight on a few mowers in the past. I'm more careful now. Old LBs are an amazing. My '88 7073 aint purty, but runs great.
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I still have my 1996 alloy deck Gold Series with the F-Series engine I bought new in 1999. I had to rebuild it once because of the connecting rod bearings being beaten to death by my son who didn't unplug it when the discharge area got clogged w/grass. About straightening a bent crankshaft, it can be done with the hammer method but I would slip a socket or pipe over it so you're not beating directly on the shaft. Also, I would use my 3# mini sledge instead of the BFH.
 
A good old fashion mower shop can straighten it with a fixture made for this. I used to help in a mower shop and we straightened crankshafts all the time. Ed
 
May possibly cost a lot in some areas of the country, but the small engine place I've gone to in the past charges $25-40 for most small jobs like that.
 
Before I retired I straightened a lot of crankshafts with the jig that I bought to many years ago to remember. Never had one break after straightening. I charged $20 to straighten it after the engine was off and everything was off the shaft.
 
My Kawasaki powered snapper bent the crank the same way. I used a 5 pound sledge and worked it straight. The blade was bent too. That, I was unable to fix, even with hyd press.

Worked well for a very long time. Then it happened again. Straightened it again and off I went. The engine eventually blew a head gasket and was so worn out I replaced it with a Honda engine.
 
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