Can a bent crankshaft be straightened succesfully?

Texas rose · 10-14-2009, 03:14 PM

Howdy folks, whilst keeping my neigbhours grass trim I had the misfortune to run over a 2" diameter steel tube imbedded in the grass with about 2" sticking proud.

The Maculloch self drive lawn mower came to an instant stop. When pulling the starting cord it was obvious something was wrong. The blade and boss has definately got a 'throw out' and catching the casing, so I took the engine cover off, only to find that the flywheel is doing concentric things also.

This is a Tecmuseh engine; now my cunning plan was, remove the crank and try to straighten it...is this possible...after all it bent easily enough?

This mower was working brilliantly up to this point, so I am loathe to part company with it. I do have access to a B&S 4hp 'Quantum' engine from a 'run over' lawn mower - possible engine change?

Could be a worthwhile 'Winter project', any thoughts?

Regards,
Texas rose.

**wrench97** · 10-14-2009, 03:58 PM

A crank shop may be able to straighten it, but I doubt it'll be worth the cost, if anything look for a used one at local mower shops or eBay/Craig's list.
As for the swap check the mounting and controls if they look the same it may be doable.

**K-B** · 10-15-2009, 06:11 PM

With special tools...yes. (There is such a tool as a crankshaft straightener). However, it is rather risky, especially if the shaft is badly bent. It will always be weaker where it bent, which is a safety hazard - - the reason why few shops are willing to bother straightening crankshafts. There are times when it will need a new oil seal, too.

If you don't get it perfectly true, it will set up a vibration that will eventually literally shake the engine to pieces.

10-14-2009, 03:14 PM	#1 (permalink)
Texas rose Registered User Join Date: Nov 2008 Posts: 80 OS: Vista	Can a bent crankshaft be straightened succesfully? Howdy folks, whilst keeping my neigbhours grass trim I had the misfortune to run over a 2" diameter steel tube imbedded in the grass with about 2" sticking proud. The Maculloch self drive lawn mower came to an instant stop. When pulling the starting cord it was obvious something was wrong. The blade and boss has definately got a 'throw out' and catching the casing, so I took the engine cover off, only to find that the flywheel is doing concentric things also. This is a Tecmuseh engine; now my cunning plan was, remove the crank and try to straighten it...is this possible...after all it bent easily enough? This mower was working brilliantly up to this point, so I am loathe to part company with it. I do have access to a B&S 4hp 'Quantum' engine from a 'run over' lawn mower - possible engine change? Could be a worthwhile 'Winter project', any thoughts? Regards, Texas rose.

10-14-2009, 03:58 PM	#2 (permalink)
wrench97 Moderator, Hardware Team Join Date: May 2008 Location: S.E. Pennsylvania Posts: 18,348 OS: Win7	Re: Can a bent crankshaft be straightened succesfully? A crank shop may be able to straighten it, but I doubt it'll be worth the cost, if anything look for a used one at local mower shops or eBay/Craig's list. As for the swap check the mounting and controls if they look the same it may be doable. __________________ Power Supply and Selection

10-15-2009, 06:11 PM	#3 (permalink)
K-B Moderator, Linux Join Date: Oct 2005 Location: NY Posts: 2,873 OS: Vista, Ubuntu My System	Re: Can a bent crankshaft be straightened succesfully? With special tools...yes. (There is such a tool as a crankshaft straightener). However, it is rather risky, especially if the shaft is badly bent. It will always be weaker where it bent, which is a safety hazard - - the reason why few shops are willing to bother straightening crankshafts. There are times when it will need a new oil seal, too. If you don't get it perfectly true, it will set up a vibration that will eventually literally shake the engine to pieces. __________________