Using gravity.... to straighten a Crankshaft

Topics Last Day Last Week Tree View    Getting Started Formatting Troubleshooting Program Credits    New Messages Keyword Search Contact Moderators Edit Profile Administration
Model T Ford Forum: Forum 2015: Using gravity.... to straighten a Crankshaft
Top of pagePrevious messageNext messageBottom of page Link to this message  By James J. Lyons III - West Virginia on Tuesday, May 26, 2015 - 08:27 am:

We've seen the discussions on proper storage of crankshafts and how it is theorized that laying them on their side can cause them to warp. Well, about 2 years ago, I bought an NOS crankshaft that was in perfect, unused condition. The journals were exactly to spec and perfectly clean. I carefully magna-fluxed it and checked it for cracks and found nothing. It appeared to be an awesome crank to place in storage, "Just in case".

Well, just for grins, I put it on my home-made jig to check it for straigtness. This is simply two V-blocks to spin the crank in and a dial indicator for reading the run-out. I placed the probe on the center journal, spun it one complete revolution and read; 0.010"...... Wait, WHAT????

That is correct, my perfect NOS crank had a .005" arch to it. !@#!!@!%!!@ I said to myself.

Now, would I use a crank with .005" of bend to it?? YES.... but that is probably the most I'd accept. You can press on it with your fingers and bend it straight so the pressure required to hold it straight in the block is minimal.

In any event, completely disgusted that my otherwise perfect crank was warped, I coated it in oil, bagged it, and HUNG it from the rafter in my barn. That was in July of 2013.

Yesterday, I took it down and decided to re-measure the runout using the same fixture and the same dial indicator just to see what I had. Low and behold, my run-out reading is now; 0.0085".... or rather, 0.00425" of actual bend.

It appears that gravity is allowing the crank to relax and that some of the warpage could possibly have come from the crank laying on it side or standing on it's end and sagging.

Personally, I found it very interesting. Feel free to hurl your own opinions...


Top of pagePrevious messageNext messageBottom of page Link to this message  By G.R.Cheshire on Tuesday, May 26, 2015 - 09:13 am:

For Grins and Giggles hang it from the rafters again but this time put a 5 pound weight hanging from the other end... kinda like when the doc puts you in traction for your back.


Top of pagePrevious messageNext messageBottom of page Link to this message  By Dean Kiefer - Adams, MN on Tuesday, May 26, 2015 - 09:28 am:

I hope my wife don't read this, she's been trying to straighten me out for years.


Top of pagePrevious messageNext messageBottom of page Link to this message  By Walter Higgins on Tuesday, May 26, 2015 - 10:35 am:

Can we see a photo of your home-made jig? On what kind of surface did you set the v-blocks?


Top of pagePrevious messageNext messageBottom of page Link to this message  By Jim Thode Chehalis Washington on Tuesday, May 26, 2015 - 11:35 am:

My guess would be differences in temperature in the crank caused the different measurements rather then how the crank was stored. Very small differences in temperature in the crank on one side or the other can be measured as changes in the straightness.
Jim


Top of pagePrevious messageNext messageBottom of page Link to this message  By Roger Karlsson, southern Sweden on Tuesday, May 26, 2015 - 11:36 am:

I don't know where the idea to store the cranks standing started? I think it would be dangerous since it's so easy to trip them over. Storing them hanging sounds safer plus clashing into a hanging crank may ring, and that's a much more pleasant sound than a falling over crank that may hurt your toes :-)

Sorry, but I can't see any possibility such a strong steel part could possibly bend from its own weight, or even if a few pounds of other stuff lies upon it?
Plastic parts can creep with age if under pressure, especially if it's hot, that I could agree upon, but not steel if it's stored at far below yield strength.

Jim's idea about uneven temperatures sounds plausible?

(Message edited by Roger K on May 26, 2015)


Top of pagePrevious messageNext messageBottom of page Link to this message  By James J. Lyons III - West Virginia on Tuesday, May 26, 2015 - 12:09 pm:

If there is agreement that a crankshaft will warp over time from lying on its side, then there is plausibility to the theory of it relaxing if opposite forces are applied.

The dimensional change in run-out over temperature is a function of the CTE delta triangulation over half the length OD the crank times the runout. I don't think the math will support the change in temperature theory but it might. I'll calculate it tonight and post what I come up with. I'll also try to post a pic of my rig for measuring the runout.


Top of pagePrevious messageNext messageBottom of page Link to this message  By Herb Iffrig on Tuesday, May 26, 2015 - 12:14 pm:

I had a crank shaft for a model T laying around the shop a few years ago. A friend of mine came by and saw it laying there and got a piece of baling wire and hung it up without asking me about it.
Her said that is what you should do.
I know I was at a tractor salvage yard in Germantown Illinois and saw that they had their crankshafts hanging by hooks from on a rack. So there must be something to the theory, or it just won't hurt to do it any way.


Top of pagePrevious messageNext messageBottom of page Link to this message  By Hal Davis-SE Georgia on Tuesday, May 26, 2015 - 12:18 pm:

I have a friend who runs an automotive machine shop. He does a lot of diesel truck and tractor work and his shop is littered with crankshafts all standing on their end on the floor. Some look 3-4 feet high. Scares the heck out of me to walk through there. I've never asked him, but SURELY one gets knocked over from time to time.


Top of pagePrevious messageNext messageBottom of page Link to this message  By Tim Eckensviller - Thunder Bay, ON on Tuesday, May 26, 2015 - 12:48 pm:

If laying down a crankshaft bends it, wouldn't hanging one stretch it and standing one compress it?


Top of pagePrevious messageNext messageBottom of page Link to this message  By Hal Davis-SE Georgia on Tuesday, May 26, 2015 - 01:03 pm:

I could see where the moment arm of any forces from gravity would be less with it stored in a vertical position. They would be limited to the 'throw' or half the stroke, where if it were lying down and supported only on each end, then the moment arm is half the length. Perhaps this where it comes from?

Along the same lines, why do they say a battery will go dead if you set it on concrete? I don't believe this one for a second. I don't know enough to say on the crankshafts.


Top of pagePrevious messageNext messageBottom of page Link to this message  By Kohnke Rebabbitting, Clare, Iowa on Tuesday, May 26, 2015 - 01:06 pm:

There are very few things that are safe from sag, from there own weight.

Cams, cranks, lathes, align bores, ect.

Just a mater of fact.

Herm.


Top of pagePrevious messageNext messageBottom of page Link to this message  By Richard Gould, Folsom, CA on Tuesday, May 26, 2015 - 01:35 pm:

I think about how finger pressure can deflect a crankshaft and question the significance of a couple thousands bend in operation. I think about the pressures placed on a crank from combustion and wonder how a slight bend can be important. I've heard that a bend will cause premature bearing wear but I don't see it. The slight pressure exerted on the bearings from a couple thousands bend is very small compared to the pressure caused by combustion.


Top of pagePrevious messageNext messageBottom of page Link to this message  By keith g barrier Savannah Tn. on Tuesday, May 26, 2015 - 02:00 pm:

I straightened mine in the 24 over six years ago on my press, still going strong after 50k. KGB


Top of pagePrevious messageNext messageBottom of page Link to this message  By Norman T. Kling on Tuesday, May 26, 2015 - 03:44 pm:

That crank might have straightened while in service if it straightened while hanging. I do, however, see a potential problem if the 4th main is quite worn, or if the crankcase is out of alignment. In the case of a misaligned 4th main, the crankshaft would bend with each revolution causing metal fatigue to eventually break the crankshaft.
Norm


Top of pagePrevious messageNext messageBottom of page Link to this message  By Jim Rose on Tuesday, May 26, 2015 - 07:41 pm:

I have installed numerous new Cummins crankshafts and they came in a cardboard box with nothing being said about keeping them upright. Engines the size of truck engines do not seem to have a problem with sagging but large stationary and marine engines have to be shimmed properly or they will sag with disasterous results.


Top of pagePrevious messageNext messageBottom of page Link to this message  By john kuehn on Tuesday, May 26, 2015 - 08:10 pm:

At the local engine rebuild shop that has been here in town since the 50's and does all sorts of engines: tractor, automotive, industrial and etc.

If you look in their storage rooms the crankshafts are stood up on the flywheel ends in rows.
That's the way this shop stores theirs anyway.


Top of pagePrevious messageNext messageBottom of page Link to this message  By Bud Holzschuh - Panama City, FL on Tuesday, May 26, 2015 - 08:37 pm:

If two years of hanging vertically reduces the runout by .005", what would several months of suspending it by the center journal do ? This assuming its rotated so the center bend is "down".

Would make an interesting experiment as the straightening force should be many times that realized by hanging vertically.


Top of pagePrevious messageNext messageBottom of page Link to this message  By James J. Lyons III - West Virginia on Tuesday, May 26, 2015 - 08:53 pm:

Here is a picture of my home-made fixture for measuring the crankshaft runout. The crank in the picture is an old rusty one that is posing as a stunt double... The fixture is stronger than you think so my numbers are correct. Besides, I checked it on a bench lathe with two metal v-blocks first and that was the inspiration to build this and see if it works. You'll notice an aluminum button that the inside thrust surface rides against so the cranks isn't sliding back and forth while in rotation.

I did the calculations to eliminate thermal changes as the root cause. Steel changes about 12 millionths per linear inch per degree C. So based on those numbers, the crank is only shrinking over length to the center journal by about 1.5 Ten-Thousands. THat's about 4 microns... super small. So the change in runout over the last two years is coming from something else.

The NOS crank is hung back in the rafters and unless it gets pressed into service, I'll pull her down in two more years and see what we have.

An interesting topic for sure!crank


Top of pagePrevious messageNext messageBottom of page Link to this message  By Jim Thode Chehalis Washington on Tuesday, May 26, 2015 - 10:05 pm:

James,
About temperature differences. It sounds like your calculation assumed that the whole crankshaft was at the same temperature and that if the temperature changed that the overall size would change very little. I think that is correct.

However think of what would happen is there were different temperatures in the crank from different measurements. For example assume that at one time that the metal on one side of the crank was one degree different then the other side (top side and bottom side in the photos). This would make the top side about 0.0003" longer and would produce about a 0.003" run out.

To get your observed change it would only take about 1/4 degree difference in the temperature to produce your observed change from 0.005" to 0.00425". At this point you could remeasure the crank a few times at different times to see if you get exactly the same reading and that would verify your current reading. However you have no way to verify that the reading was correct that was made two years ago.

If there was any very small temperature differences in the crank when the first measurement was taken that would trough off the ability to compare the real change in the crank now.

Jim


Top of pagePrevious messageNext messageBottom of page Link to this message  By Dan Treace, North FL on Tuesday, May 26, 2015 - 10:21 pm:

Ford works in 1915, engine assembly, cranks are stored upright.....



Saves space sitting under the assembly bench too.
Bet these didn't sit too long :-)


Top of pagePrevious messageNext messageBottom of page Link to this message  By Walter Higgins on Tuesday, May 26, 2015 - 10:26 pm:

With all due respect, you really ought to use a matched set of v-blocks on a granite surface plate for repeatable comparison. Ideally, it really ought be be held between centers. If it were a worn crank with various journal dimensions and runout, that really complicates matters.


Top of pagePrevious messageNext messageBottom of page Link to this message  By Frank van Ekeren (Australia) on Wednesday, May 27, 2015 - 01:48 am:

Walter, sorry, not so, holding between centers will give a false reading, V blocks is the right way.


Top of pagePrevious messageNext messageBottom of page Link to this message  By Frank van Ekeren (Australia) on Wednesday, May 27, 2015 - 01:59 am:

Found the reference to what I posted before.


Top of pagePrevious messageNext messageBottom of page Link to this message  By Walter Higgins on Wednesday, May 27, 2015 - 08:38 am:

Frank, there is also plenty to the contrary, right and wrong ways to do both, and plenty of variables to take into account with both depending on set-up. I didn't outright shoot down using v-blocks. However, mounted on wood v-blocks on a plywood cradle introduces variables that cannot be controlled or repeatedly assessed.


Top of pagePrevious messageNext messageBottom of page Link to this message  By Paul Vitko on Wednesday, May 27, 2015 - 10:28 am:

I use a T block upside down with the front main and rear main cap upside down with cap bolts slipped in holding the caps the right distance apart. with the dial mounted to the center of the block the mounts are ridged. With a little light oil on the Babbitt caps the crank does not try to climb the cap radius changing the measurement.

When straightening a crank the block is stuck in the press with the crank in as described above then pressed with increasing amounts of pleasure until the crank can be rotated 360 degrees with very little run out showing on the center main. Pressing straight just a few thou of run out might take a bunch more then a few thou in the opposite direction.


Top of pagePrevious messageNext messageBottom of page Link to this message  By Chris Paulsen - McPherson, KS on Wednesday, May 27, 2015 - 10:43 am:

Harold Sharon wrote a great chapter in his book "Understanding your Brass Car". The chapter is titled "Myths, Old wives Tales, Mistaken Beliefs & Outright Lies".

He wrote a paragraph about sagging crankshafts. To summarize, if it were possible, think about how much your thinner camshafts would sag, especially with the added pressure of valve springs on them. How about the also thinner rear axle shafts? Neither of these seem to sag after years of sitting.

And how about all of the 4-cylinder engines that has just two main bearings, they would certainly sag more, would they not?

Just passing along some thoughts.


Top of pagePrevious messageNext messageBottom of page Link to this message  By Roger Karlsson, southern Sweden on Wednesday, May 27, 2015 - 10:58 am:

There is certainly a difference between sagging a miniscule amount from its own weight or from handling compared to getting permanently deformed.

To become permanently deformed, a crankshaft has to be bent with a force that goes above the yield strength of the steel - and then we're talking about perhaps 400 MPa, nothing you'll achieve without a press.


Top of pagePrevious messageNext messageBottom of page Link to this message  By Nicholas Lingg - Tarboro, NC on Wednesday, May 27, 2015 - 11:32 am:

Lay it in the sun for 15 minutes and measure it then lay it the sun for 30 minutes recheck it then a hour. Let us know what you find out.


Top of pagePrevious messageNext messageBottom of page Link to this message  By Ken Todd, ............Red Deer, Alberta on Friday, May 29, 2015 - 06:10 pm:

"then pressed with increasing amounts of pleasure"

OK


Top of pagePrevious messageNext messageBottom of page Link to this message  By Ken Todd, ............Red Deer, Alberta on Friday, May 29, 2015 - 06:15 pm:

It sounds like some of you fellows are hanging cranks w/a wire in a flange hole.
FWIW, an old timer once told me that the proper way was 2 parallel boards level and horizontal w/enough space between them to slide the rear main through and the crank suspended by the flange. Like some people do w/wine glasses.
Any opinions on the pros/cons of either method?


Top of pagePrevious messageNext messageBottom of page Link to this message  By Roger Karlsson, southern Sweden on Friday, May 29, 2015 - 06:25 pm:

The most important factor when storing a crank in the real world must be rust. Too many otherwise good cranks has been ruined by rust on the bearing surfaces. Paint, grease, wrap them in plastic or whatever needed to avoid rust when storing parts like cranks and camshafts in a unheated shed.. Having to grind a crank just because of easily avoided rust adds cost and reduces crank life.

How it hangs, stands or lies on a shelf won't make any difference.


Top of pagePrevious messageNext messageBottom of page Link to this message  By Walter Higgins on Friday, May 29, 2015 - 06:36 pm:

+1 to what Roger said.


Top of pagePrevious messageNext messageBottom of page Link to this message  By Charlie B actually in Toms River N.J. on Friday, May 29, 2015 - 06:47 pm:

I vote for temperature variations. As to upright storage as shown in the Ford photo: probably just convenient. True in a lot of cases.


Top of pagePrevious messageNext messageBottom of page Link to this message  By Niels Andersen on Sunday, July 12, 2015 - 07:54 am:

I am just about to assemble an engine! -
Based on James's way of measuring crankshaft warpage, where he read 0.010", I reed 0.0066" equal to an arch of 0.0033". - Is that too much to use it as it is?
I have tried to apply weight to the the middle main journal with the shaft ends placed in V blocks: First 10 kilos for 10 days and then 30 kilos for 2 weeks, without any reaction.


Top of pagePrevious messageNext messageBottom of page Link to this message  By Royce in Georgetown TX on Sunday, July 12, 2015 - 09:17 am:

Niels,

You don't have a problem.


Top of pagePrevious messageNext messageBottom of page Link to this message  By Kohnke Rebabbitting, Clare, Iowa on Sunday, July 12, 2015 - 08:47 pm:

003 thousandths is a long way to have a center main out.

The pressure from the high side will wear the babbitt with that constant bowed pressure.

With that pressure it will also push the oil a head of it, rather then letting it surround the shaft equality


Top of pagePrevious messageNext messageBottom of page Link to this message  By Kohnke Rebabbitting, Clare, Iowa on Sunday, July 12, 2015 - 08:49 pm:

003 thousandths is a long way to have a center main out.

The pressure from the high side will wear the babbitt with that constant bow pressure.

With that pressure it will also push the oil a head of it, rather then letting it surround the shaft equality


Top of pagePrevious messageNext messageBottom of page Link to this message  By Tony Bowker, Ramona, CA on Sunday, July 12, 2015 - 09:19 pm:

I seem to remember that Ford allowed 0.010" run out on the crankshaft. Could be wrong!


Top of pagePrevious messageNext messageBottom of page Link to this message  By Kohnke Rebabbitting, Clare, Iowa on Monday, July 13, 2015 - 12:00 am:

Ford said, if the shaft was out more then .012, a new shaft should be installed.

If less then .012, it should be straightened on a press.


Top of pagePrevious messageNext messageBottom of page Link to this message  By James J. Lyons III - West Virginia on Monday, July 13, 2015 - 07:01 am:

I read once on a thread where someone put a dial indicator on the hogshead to measure deflection under load. If I remember correctly, they found that the gap between the engine and the hogshead gyrated WILDLY during acceleration and de-acceleration, showing that there was tremendous bow and flexing between the U-joint and the third main. If his set-up was correct, that means the transmission is moving back and forth putting tremendous strain on the back flange of the crankshaft WAY MORE than .003. Which also mean that .003" of bow at the center main is meaningless.


Top of pagePrevious messageNext messageBottom of page Link to this message  By James J. Lyons III - West Virginia on Monday, July 13, 2015 - 10:33 am:

Actually, The transmission is moving "up and down"... not back and forth as I said above. My bad.


Posting is currently disabled in this topic. Contact your discussion moderator for more information.
Topics Last Day Last Week Tree View    Getting Started Formatting Troubleshooting Program Credits    New Messages Keyword Search Contact Moderators Edit Profile Administration