The Stovebolt Site Forums The Shop Area Engine Shop crank shaft repair

I am getting the 216 from my 1950 3100 rebuilt and was just informed by the shop that the crank shaft was bent and he needed to send it off to get it straightened by some shop with a special press. He couldn't quote me a price for this process until they told him if it could be straightened or not. Has anybody had this done? I have to think that this is type of part is at risk of future failure if it is being manipulated this way. would it be better to just replace it or are there decent shafts available to replace it? I went with this shop because they do warranty their work so I guess if they are comfortable with it then it must be ok but I would lke another opinion if anybody has one. Thanks

Eric

I dunno about a long crank, but years ago a buddy had a Pontiac 400, found out the crank was bent during a basic rebuild, it was sent for straightening & it worked fine for many years(may still running be somewhere). Brian

Straightening a crankshaft is a routine procedure for just about any automotive machine shop that welds and grinds cranks. Unless the 216 crank is forged instead of cast, however, it does not belong in a press. Cast cranks are straightened with a hammer. Forged crankshafts are straightened in a press. Put a cast crank in a press, and it will crack! In the shops where I've done this kind of work, we would sometimes straighten BIG cranks, like an 855 cubic inch Cummins, or one of the Catepillar bulldozer cranks by pressing, but straightening most automobile cranks was done with a big lead hammer, with the crank suspended on each end by brass V-blocks.
Jerry

I would get an estimate on the cost of straightening, and compare that with the cost of finding, cleaning and inspecting a second crankshaft.

I think it is fine to have it professionally straightened, but I would not if there is a cheaper way.

Grigg

I find it very supisous that a crank can be straightened. Cast iron is hard and does'nt bend it breaks.

Beaver,


Cast iron is brittle...I think the cast crankshafts are cast steel...much tougher!

Stuart

Beaver, crankshafts are not the same alloy as engine blocks, heads, etc. Nodular cast iron has a different grain structure, and yes, it bends. It can't be forced into a right angle, or anything like that, but we're talking about a deflection of a few thousandths, maybe the thickness of a couple of strands of hair. A sharp blow with a soft, blunt object like a lead hammer will definitely take a minor bend out, and I've done it as a routine part of regrinding or rebuilding damaged crankshafts. What's your engine machining background? I've been doing it for a little over 40 years.
Jerry

Thanks to everyone. I still don't have a price but I do feel better about the repair if they do it that way.

Hotrod, Don't mean to question your expertice in any manor. I have been a welder for over 40 years and have seen miricals done by many good people like yourself. I've done some myself, but not going to put a straighten crank in any engine I rebuild. Not worth the chance. After all I am the guy that stands behind my product. I am the owner. I'm the guy that answers the phone.

I have used professionally straightened crankshafts before, and so far have never had a problem with one. This has been both for me and for the public.

So how and where does a crankshaft bend? Is this from running with worn out mains?

A miracle! I like it. Metal components from numerous applications are manipulated precisely with heat and pressure everywhere and everyday. This is pretty basic stuff and there’s no real issues other than straight or not straight. It’s good the builder recognized something that needed someone and the tools to know what to do. Radial impact like a backfire is the most likely suspect for bending and a smack in the opposite direction is the cure. If I was spending money on a crank it would be a drilled one from a 235. Good luck.

Curt B.

Fred, castings continue to normalize over their life. Jerry made the point that it's usually only a few thousands. Bridgeport Milling machine base castings used to lay out in the field for two years before they were stable enough to bring them in and start the machining on them. Blocks and head are almost always warped up a little over the specs when down for a rebuild. Line boring is as common as decking, head milling or crank straightening and again is very often due simply to the castings normalizing. We tend to think that iron/steel is absolutely stable material and that it doesn't move around but like all materials it is plastic to some degree. When you subject the structure to cyclic heat and vibration it wants to eventfully settle into a relaxed state, aka, warp.
Denny Graham
Sandwich, IL

I'm also a welder, having worked as a fabricator and pipefitter for E.& J. Gallo in the world's largest winery for several years, where we ran 4" stainless tubing, fitted and TIG welded in place by the mile. Heating and cooling over repeated cycles will stress any type of metal, including crankshafts. One of the first checks an engine machinist makes before regrinding a crankshaft is to suspend it on V-blocks at each end, and check a main bearing journal near the center for runout. Minor problems can be dealt with by straightening. A severe bend is grounds for discard. Even with assembly jigs, some weldments have to be scrapped due to distortion, while others can be straightened by judicious heating and bending, right? Nothing different in the crank straightening business!
Jerry

This is great, I am doing a lot of learning here!

Denny you're referring to cast iron which is one of the most stable metals. Nearly all machine tool tables/bases are made of cast iron for this purpose. Jerry is referring to a forged steel crankshaft which is an entirely a different animal altogether. Although not visible to the eye metals change composition drastically depending on how they are worked. All metals and thier alloys have different thermal characteristics. Nobody magically came up with what works. Welding, heat treating, and normalizing procedures are done by engineers. Here's some good metallurgical info:

http://www.mmsonline.com/onlinetools/

Curt B.

Actually, I have experience with both cast, and forged crankshafts. The straightening procedures that work on forgings definitely won't succeed on a casting, and vice versa. After building up the journals with a swubmerged-arc crankshaft welder on a Caterpillar D-6 crankshaft that stands over 6 feet tall, and weighs a thousand pounds or so, it's often necessary to use a 10-ton hydraulic press and a rosebud torch to get the main bearings close enough to alignment to allow the regrinding process to proceed. That's a forged shaft. The crank for the old 216 is a casting, and it would crack if it's straightened in a press. Like it or not, all protests aside, CAST IRON BENDS! Experienced crankshaft technicians have been straightening cranks with hammers for longer than any of us have been alive. It works!
Jerry

I've actually seen the process of staightening cranks at a regrinder's shop, it's actually neat to watch. They do cams the same way, only on smaller equipment. I wouldn't have an issue wiht a staightened crank if it was done by a pro.
BTW-All 216,235,261 cranks are forged, not cast.

Bill, interesting bit of information, I would like to know how you discovered that? I know this is a little off subject but since we were discussing the stability of castings and the blocks and heads are castings this may be appropriate. Much of the time these are warped also.
Although the following link is a discussion about wood working machines, I believe the metallurgical aspects of it do add to our discussion; http://www.sawmillcreek.org/showthread.php?t=19751
Another interesting site is taken from the previous link; http://www.meehanite.com/
Here is a page out of a very old book, “Modern Toolmaking Methods” 1915. much of this still applies to the vintage castings that we are working with; http://rides.webshots.com/photo/2150977240098611668WmWoBn

Our knowledge of Metallurgy technology is being up dated daily. As a result we are producing much better castings today than we did 60 years ago. So I think we have to remember that most of the castings that we are considering here were poured 50 or 60 years ago.
Denny Graham
Sandwich, IL