Is it ok to straighten a bent crank

I had a rod bearing freeze up in my 68 440 a couple months ago. My engine is at an engine shop. I stopped over yesterday and the machinist told me the crank (forged) was bent (something like 8 hundreths) but he was able to straighten it out. Is this something I should be concerned about. The engine was around 420 horsepower at the crank before freezing up. It only had around 500 miles on it and the pistons, cam etc are still good so I am going to have about the same HP when re-assembled.

No problem, very common procedure.

Is it ok to straighten it, sure. Can he? That's another thing all together.

He says "8 hundredths", that's .080" - which is over 1/16". I've had lots of experience straightening axles for race karts and I can tell you that getting within a few thou is easy but getting "dead on" could literally take hours. In my opinion, any crank that is straightened would only be "close" and would then need to be ground. Not only will the mains need to be ground an polished but the rod journals need to be done to correct things there too. In the end a new crank can be less expensive.

If the crank breaks it will be during the straightening procedure..

Friends Z28 ( 69 - 302) came back in two pieces from the machine shop, back in the day....

An expensive setback when its your High School daily driver..LOL

Cranks get straightened all the time by machines shops. (usually only by a guy with gray hair though!)

It is a crude process where you put the crank on some V blocks in the hyd press and then you guess at how hard you have to push it. You have to push it past center so it springs back to dead even. Push it too far and it bends the other way. Bend it back and forth too many times and it breaks.

The guy has had his machine shop since the 60's and they have all sorts of engines that he works on. So he is a guy with grey hair and has a very good reputation around here. The shop is Darr Engines in New Orleans. I may give him a call later today and see how it is going.

That's why it can take hours to get it dead on. However, breaking a "forged" crank by trying to straighten it is unlikely unless the thing is bent in half!! Cast cranks aren't worth trying and will snap - likely what happened to that chevy crank!

Pretty sure a factory Chevy 302 had a forged crank.

Can't see breaking a forged crank. If they handed it back in two pieces it was likely cracked to begin with and trying to straighten it sealed its fate.

Nitriding could cause a crack. ok, let me clarify, straightening a crank that has been nitrided could cause it to crack. Tim

That would explain the 302 crank, they were nitrided.

Almost any time a bearing grabs the crank and spins, it will bend the crank slightly. .008 is no that much to straighten. All good machine shops know how to straighten a crankshaft before they turn it. Easy as pie and no problems.

Thanks everyone for their opinions. I am not so worried about it now.

I'm not sure I would put a straightened crank back in my engine.
Just my 2 cents.

Yes the 302 crank was forged and I believe it had larger journals than the 283.. Remember the 302 was technically a 327 bore with a 283 crank..

Seems as if Chevy was on strike?? when this happened and as said above, this was his "daily" transportation so panic to get it fixed was happening.. NO 302 cranks around so we looked into using a 283 crank.. Wasn't gonna work...

Yeah, the 302 used the 283 stroke but the larger journal sizes, and that it way more chevy info than I wanted to know.

As probally already mention whne you spin a rod bearing the heat warps the crankshaft, a forged steel crank will bend but it can, and should be be straighten in a press safely before grinding the mains or rod journals I had one 1969 440 crank out of a CA Hiway Patrol car that had spun a rod bearing, I took it to my crankshaft grinding company and watch them try to straighten it in the press before setting it up for grinding, that rascal broke in the middle Far better for it to break in half there than in the motor

I always heard when a bearing spins it forms a crack from the heat, got a hemi Kellogg crank with that problem. Better check for cracks, mopar is famous for that.

Magnaflux it, using magnetic particle, not dye penetrant before it is ground, to see if it's worth saving. If it's been ground, dye penetrant should show you any cracks. That goes for any crank.

The overheating CAN cause cracks, really it's probably the uneven cooling that does it, but it doesn't have to. Lots of steel things are forged at red heat or a little hotter, and they don't have cracks. For example look at the Callies ad for its connecting rods where they show you a rod blank during the forging process.

If you can afford it I would strongly suggest getting a 4340 crank, either new or slightly used. It will be 50% or more stronger than the stock crank. I'd hate to waste all the machine work in a block to try to save a buck on the crank.

R.

As already pointed out heat from spinning a bearing can, not always, cause cracks. I have all my rotating parts magged before using them, I have had some cranks with cracks in the fillets ground out and welded up and then repaired In fact I have a old forged steel Bryant 4.5 stroke top fuel carnk with the center counterweights that is cracked in multiple places, I've got a bid of $800.00 to have it welded and repaired so it is uaseable in a street or mild bracket race motor.That crank has never spun a bearing that I can see any evidence of or the crank repair specialitis could see or tell of A new one like it starts at $3200.00 now so maybe I will have it fixed and use it