Briggs & Stratton crankshaft replacement

[Primemover88]

Engine is a 6.75 B&S Intek OHV 12S975-0144-B1

Crankshaft is bent from hitting a piece of wood. I repowered the mower with a new engine but now I have a potential use for the old engine.

I know how to replace the crank, but my question - is there a high probability that other engine parts were damaged as well?

Thanks!

[wristpin]

Can only say that I have replaced some seriously bent cranks over the years with nothing else other than a sheared flywheel key, a gasket and an oil seal to replace; and could possibly have got away without renewing the gasket and seal ! Shush!
If you are unlucky and your bit of wood was firmly anchored in the ground you just might have distorted the bottom main bearing. If after cleaning rust etc from the crank extension the lower crankcase slides of the crank easily you will almost certainly be OK. If the crank is bent severely enough that it won't slide off you may still be able to to remove the lower case by sawing through the crank as close to the oil seal as possible without damaging it. Then you will only really know if the bottom main is misaligned by the way everything goes together with the new crank (or a good used "slave" crank to test it with.

[KE4AVB]

Don't know if any shops still have them but at one time there were crankshaft straighter rigs for doing those engines on push mowers. You may check around and find a shop that willing to straighten it for you or rent their straighter to you. If they can; they do it without even taking the engine apart.

It is fairly common place for the crankshaft to be bent just below the crankcase without damage to the internals. It mostly due to reduced diameter of the shaft. Don't see many lately brought in the shop as most times users are opting for those cheap Chinese engines like HF sells for around $100 or just buying a new mower with prices being what they are here.

[bgsengine]

we have a crank straightener, have not used it in years
- The issue, even if the crank can be straightened (and on most newer engines with lighter castings, the sump often cracks when trying to straighten, anyway) - The crank can have invisible cracks and stress fractures that lead to the crank breaking off completely - not something you would like to have happen when you have a blade spinning at 19,000 feet per minute attached to it.

Considering the risk and cost (at minimum 1 hour labor plus oil seal and oil) better off just re-powering or replace the mower.
We have a goodly pile of scrapped complete engines (robbed of things like carburetors, fuel tanks, control brackets) sitting in the scrap pile waiting to be dismantled by someone and hauled away to the scrap yard.

So, generally when we explain the issues and show a worst case estimate , the cost to repair comes out to as much as or more than a replacement engine, and both are often more expensive than just buying a new mower from wal-mart or somewhere, so....

Ive thought about putting the crank straightener on eBay and see what we can get out of it, BUT it makes for a very handy work table

[Deere2me]

Engine is a 6.75 B&S Intek OHV 12S975-0144-B1

Crankshaft is bent from hitting a piece of wood. I repowered the mower with a new engine but now I have a potential use for the old engine.

I know how to replace the crank, but my question - is there a high probability that other engine parts were damaged as well?

Thanks!

The short answer is everything usually is OK. But, look, the very first thing ya wanna do is inspect the flywheel for a munged up keyway, or cracks. The internals are usually good either way, but a flywheel ain't free.
I've had good luck straightening some pretty bent cranks using an old blade adapter ( so as not to ding up the surface) and a B.F.H. It helps to have the motor bolted to a deck or something, I doubt you'll be able to whack it otherwise. And yeah, the crank can crack, but I personally have not had any problems or comebacks from it.

[Primemover88]

Thanks for all of the replies!

I think I'll remove the crank and take a look at everything before I order new parts.

Again, I appreciate the responses.

[kyfarmer]

I have had good luck using a hack saw or Sawzall to cut the crank flush with the oil seal so the "bend" doesn't get stuck in the crank bore of the sump and prevent removal. More of an issue on the little Classic and E series since the main bearing and customer bearing are very close to the same size.

[wristpin]

The short answer is everything usually is OK. But, look, the very first thing ya wanna do is inspect the flywheel for a munged up keyway, or cracks. The internals are usually good either way, but a flywheel ain't free.
I've had good luck straightening some pretty bent cranks using an old blade adapter ( so as not to ding up the surface) and a B.F.H. It helps to have the motor bolted to a deck or something, I doubt you'll be able to whack it otherwise. And yeah, the crank can crack, but I personally have not had any problems or comebacks from it.

OMG - if it's your own machine bad enough but if you're doing that to "customers' " machines, not acceptable,
let alone admitting it on a public forum!
Thought that the public liability culture originated you side of the pond!

[RoyM]

First shop I worked in had a straightener, I bolted the motor to it, turned the crank to align the high side to a jack bolt (if it would turn) then applied pressure checking my progress with a dial gauge. It worked, never had a failure I knew of, but I know better now.

[Deere2me]

The short answer is everything usually is OK. But, look, the very first thing ya wanna do is inspect the flywheel for a munged up keyway, or cracks. The internals are usually good either way, but a flywheel ain't free.
I've had good luck straightening some pretty bent cranks using an old blade adapter ( so as not to ding up the surface) and a B.F.H. It helps to have the motor bolted to a deck or something, I doubt you'll be able to whack it otherwise. And yeah, the crank can crack, but I personally have not had any problems or comebacks from it.

OMG - if it's your own machine bad enough but if you're doing that to "customers' " machines, not acceptable,
let alone admitting it on a public forum!
Thought that the public liability culture originated you side of the pond!

OMG ?????? Ain't that what them little girls use when texting each other????????? W.T.F.!