Straightening crank shaft on push mower

[motoman]

This has been interesting to see how much hidden knowledge is out there. I think the magflux step should be first, by the way. (my bad) That way cracks before straightening rule out further effort. What does , for instance, a more expensive crank cost? Worthwhile to straighten as you go upscale?

 

[Fish]

Well, in a lot of cases, you cannot easily dismantle the engine without damaging the sump or else cutting the crankshaft off.

Generally, a pushmower is not worth that much labor and parts. When I did the straightening, the deal was, if it works,
$50 plus any parts, if it doesn't, no charge, and no I am not going to put it back together free.

 

[cashman]

Back in the 1960's, we used to straighten crankshafts on a fixture kinda like yours Fish. And just about every shop back then had one! The one we had was a "LiL Brute" and it was called an engine test stand. It had a hardened sleeve that fit on the crankshaft and the bolt on the straightener pushed down against the sleeve. It worked pretty darn good! If the engine had either a real long crankshaft (+4.00")or a real short crank (-2.00"), you could easily crack the sump trying to straighten it. It worked great on cranks with a 2.50" to 3.00" PTO length. Briggs put out a service bulletin warning of the dangers of straightening crankshafts and we stopped doing it in the shop. Briggs pointed out in the bulletin that they had switched to using ductile iron instead of steel in the crankshafts and you could end up with a fracture in the crank if it was ever bent. I don't remember ever seeing one that had been straightened that broke, but I'm sure that it could happen under the right conditions. Thanks!!!

 

[Fish]

Yeah, my straightener has an equalizer bolt that comes up under the shaft close to the sump,
and the straightener bolt presses the shaft down against it, so no stress is given to the sump/bearing. The down side is that, you cannot do it on real short cranks..