Storing crankshafts

To be up front. I don't have any crankshafts to store. I was reading something about people swearing up and down that unless you store your crankshaft upright (standing up) it will warp. I've always assumed it was true, my Dad does it, always has. OK. Now I am a mechanical engineer. Why?

Can you really say that the steel or cast iron will be weak enough if stored horizontally to actually creep?

http://en.wikipedia.org/wiki/Creep_%28deformation%29

Creep is pretty slow, and has to happen under some pretty serious stress. Really? Seriously? Why does this happen? Does anyone have any actual data?

-Brian

I really don't see it happening. We are covering fatigue and such in my Machine Design class and I can't see it happening it takes a lot of stress to get it to that point.

If you put the crank on blocks at the very ends and lay it on its side, it will deflect to the direction of gravity no matter how thick. It will take a good chunk of time to get to a measurable deflection, but it will happen. The crank really doesn't have strength to guard against the deflection when laid on its side.

Really you can lay a crank on its side, but you have to accurately support the CENTER of the crank, which halves the load on the crank from gravity caused deflection. It is just a basic statics problem.

tuna55 wrote: Can you really say that the steel or cast iron will be weak enough if stored horizontally to actually creep?

Yep. It takes a good long while (a week? not a problem. a decade? HANG IT) but it does happen.

You're not supposed to store brake rotors on-end, either.

Sweet, I LOVE canoes!

Knurled wrote:

tuna55 wrote: Can you really say that the steel or cast iron will be weak enough if stored horizontally to actually creep?

Yep. It takes a good long while (a week? not a problem. a decade? HANG IT)

Happened to me once. Stored a 400 crank "temporarily" laid down for 5 years. It was junk when I went to have it machined.

Then again the same shop tried to give me a cast 350 crank instead of the forged one I dropped off-always stamp your parts before dropping them off

Yeah, I've got a Chevy 265 crank at home, you know, a great crank for turning a small journal 327 into a 302 with. But it's been stored on its side for at least 30 years. So not only is it a rusty forging, it's also warped and trashed.

pres589 wrote: Yeah, I've got a Chevy 265 crank at home, you know, a great crank for turning a small journal 327 into a 302 with. But it's been stored on its side for at least 30 years. So not only is it a rusty forging, it's also warped and trashed.

It looks like you can take the crank from the 4.3l version of the LT1 and throw it into an LT1 to make a modern 302.

In reply to Knurled:

Time to find myself a Volvo 142, a Muncie M-21, and some LT1 bits!

always store cranks up right, no matter what! it can be argued that if a crank is stored on its side for a short while it can be straightened and/or machined out, however as someone who works at a machine shop, its really good practice to get in a habit of always storing cranks upright. if you develop bad habits then your freshly machined crank can be stored on its side for maybe a couple of weeks before the motor is assembled, and the "creep" will only cause saaay .0005 deflection, but the stresses inside the engine will turn that into .005 real quick and then ur in a pickle

Nobody is answering the question with actual science, engineering or data. Anyone have any actual proof?

tuna55 wrote: Nobody is answering the question with actual science, engineering or data. Anyone have any actual proof?

Sounds like a job for Mythbusters!

I have had one stored on its side on a shelf for 3yrs... going to build the motor this winter. If the crank is not true, I'll be surprised.

I've had a Spitfire crank stored on its side for several years. Think I can turn it over and get it to sag back the other way?

Halfway through the storage period, ROTATE the crank 180 degrees. Problem solved!

I think that supporting the center is a good idea, cranks are "stored" sideways in your engine, with proper support I know.

As far as creeping, you need to know about temperature, time and load (assuming no fluctuations, which is a big PITA in itself). Assuming garage temperatures don't vary too much, you'd need a big load. How heavy of a crank are we talking about here?

tuna55 wrote: Nobody is answering the question with actual science, engineering or data. Anyone have any actual proof?

Actually, I did. it is a very basic bridge-esge statics problem. You have force acting on the system, gravity and crankshaft weight, acting in the center of the unsupported span, middle of the crank in this case. Then after a bunch of seemingly trivial math, based from you force diagram, you end up with how the forces are acting on your object. Then after some more math, involving material strength and thickness, you end up with either something broken or holding its own just fine, but bending in the direction of the force applied.

Easy visual is to use a piece of string and a significantly weighted nut. Place the nut in the middle of the string, then attempt to pull the string taunt horizontally. You will see that the nut always droops a bit even though you have the string to the point of breaking. Eventually, your crankshaft will do the same. Reason is the unsupported span doesn't have either enough mass in the vertical direction to avoid the deflection or doesn't have enough mechanical properties, total material strength or already deflected in the opposite direction, to resist the deflection either.

I know i am probably missing something in this explanation, but it's been at least 15 yrs since I took statics.

Brian

Ranger50 wrote:

tuna55 wrote: Nobody is answering the question with actual science, engineering or data. Anyone have any actual proof?

Actually, I did. it is a very basic bridge-esge statics problem. You have force acting on the system, gravity and crankshaft weight, acting in the center of the unsupported span, middle of the crank in this case. Then after a bunch of seemingly trivial math, based from you force diagram, you end up with how the forces are acting on your object. Then after some more math, involving material strength and thickness, you end up with either something broken or holding its own just fine, but bending in the direction of the force applied. Easy visual is to use a piece of string and a significantly weighted nut. Place the nut in the middle of the string, then attempt to pull the string taunt horizontally. You will see that the nut always droops a bit even though you have the string to the point of breaking. Eventually, your crankshaft will do the same. Reason is the unsupported span doesn't have either enough mass in the vertical direction to avoid the deflection or doesn't have enough mechanical properties, total material strength or already deflected in the opposite direction, to resist the deflection either. I know i am probably missing something in this explanation, but it's been at least 15 yrs since I took statics. Brian

Yeah man, I am pretty sure that qualifies as "not using science".

Part of the creep equation is time. Anything is under stress, sure, but creep is for measuring bridges and buildings that will be up for hundreds of years and are under considerable stress. The most the crank can be on is the moment formed by the 45 lbs of crank weight on the thinnest journal/counterweight cross section, there's just nothing there.

So, what I am hearing is the same stuff, and nobody has measured anything.

Maybe ask here? http://www.eng-tips.com/threadminder.cfm?pid=71

That site seems to be populated by PEs who work in the auto industry...

there is no better place for a crank... then in its block

no bend, no creep, no walk.....

As Goldilocks says...

.....just right

I'm going to have to go check my engine. I may have left one crank in the block sitting on half of a bearing shell. If I did i will be proud of myself.

Not to burst everybody's bubble, but...

Crankshafts have these things called counterweights. So when you lay one down, it actually is supported in the middle. The "span" would pretty much be 1 or 2 journals.

I'll just leave this here...

Javelin wrote: Not to burst everybody's bubble, but... Crankshafts have these things called counterweights. So when you lay one down, it actually *is* supported in the middle. The "span" would pretty much be 1 or 2 journals. I'll just leave this here...

Exactly. So the thing isn't exactly a noodle.

I was going to suggest that. Sounds almost like storing a battery on cement.

Stored many automotive cranks for many year w/o issue. None. Now at work, we have cranks that are 21' long, they are heavy enough to creep. Turbine shafts will too if they are stopped hot with out going on turning gear.