2 Piece Crank

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Model T Ford Forum: Forum 2012: 2 Piece Crank
Top of pagePrevious messageNext messageBottom of page Link to this message  By Doug Money - Braidwood, IL on Friday, September 14, 2012 - 11:18 am:

And yet another 2-piece crank for your viewing. This is not mine, it belongs to a friend. He was driving along about 30 and 1/4 throttle and it snapped.



Top of pagePrevious messageNext messageBottom of page Link to this message  By Doug Money - Braidwood, IL on Friday, September 14, 2012 - 11:20 am:

The rust droplets formed from sitting after the fact.


Top of pagePrevious messageNext messageBottom of page Link to this message  By Roger Karlsson, southern Sweden on Friday, September 14, 2012 - 03:05 pm:

Did something in the block break too, since there must have been some force forwards and rearwards with an angled break like that? :-(


Top of pagePrevious messageNext messageBottom of page Link to this message  By Doug Money - Braidwood, IL on Friday, September 14, 2012 - 04:01 pm:

No damage to the block. Just the crank.


Top of pagePrevious messageNext messageBottom of page Link to this message  By Doug Money - Braidwood, IL on Sunday, September 16, 2012 - 05:52 pm:

Any guesses on what could have caused it?


Top of pagePrevious messageNext messageBottom of page Link to this message  By Roger Karlsson, southern Sweden on Sunday, September 16, 2012 - 07:00 pm:

The Model T crankshaft isn't properly designed against metal fatigue. Should have had beefier journals. Ford didn't know better in 1907 & didn't want to change the journal sizes after he learned.

1924-27 cranks are somewhat beefier in between the journals, though, and 1927 "EE" marked cranks seems to have a better steel composition, so there were some improvements during production. The bolts connecting the hogshead and the engine block in 26/27 should also lessen the fatigue loads on the crank's rear flange.


Top of pagePrevious messageNext messageBottom of page Link to this message  By Dan Knoll on Sunday, September 16, 2012 - 09:52 pm:

Don't think J-B weld will fix that ...that's to bad ...good it didn't ruin anything else !


Top of pagePrevious messageNext messageBottom of page Link to this message  By Anthony Bennett on Sunday, September 16, 2012 - 10:47 pm:

welcome to the club... :/


Top of pagePrevious messageNext messageBottom of page Link to this message  By Alan George Long on Sunday, September 16, 2012 - 11:28 pm:

That's one reason i have installed a Scat crank to my open 1910 valve engine. Broken crank is bad enough without the chance of taking the valuable block with it

Alan in Western Australia


Top of pagePrevious messageNext messageBottom of page Link to this message  By George_Cherry Hill NJ on Sunday, September 16, 2012 - 11:33 pm:

Doug,

I use to ask the dead be sent to me, but then the UPS guy got a hernia and folks were not telling me they were coming...

My second offer was to usually ask for a bunch of straight on photos with lot's of light, I'd mark them up and show things like starting point, etc...but that takes a bunch of time on my part and most don't like my diagnosis anyway! :-)

So...here's a hint...

In your photo as they are I 'see' that this puppy went for while in 'bending', (i.e., a main was loose with probably the 4th pulling on it at the same time)

The clue? Unlike most of my previous reviews that were obvious relief errors or nicks, look at all those 'second' marks around the OD in the lower pic! That's fatigue limit in bending as the primary cause...

My guess is it 'may' have been compound fatigue...the lightning streaks around the OD are from bending and would have grown until the core was about the size of the stub tear off you see and then let go at some point in time anyway.

But you can look closer at 6 o'clock in the lower photo on the real one...look with a glass...the center of the oyster shell 'focus' is there on the OD at 6 o'clock. That 'could' have been one of those second marks that just happened at a bad spot on the fillet, or at a skip via grind, or a nick in handling and gone from there faster than the others were progressing from the outside in.

The amazing thing that I try to teach is that these cranks were plenty big enough for the HP and Torque. It's how they are worked and mounted and yes....I'm not sure that Ford yet knew how to design where actual fatigue limit would be near infinity if NOT bent in use.

Look at other samples in search...the 'stub' generally has the SAME cross section area...thats the point where it all said 'oops'...too small good stuff left to handle what is being delivered and went pop'


Top of pagePrevious messageNext messageBottom of page Link to this message  By Rob Heyen - Nebraska on Sunday, September 16, 2012 - 11:50 pm:

Doug,
Sorry for your misfortune.

George,
Tremendous analysis. Thank you,

Rob


Top of pagePrevious messageNext messageBottom of page Link to this message  By Doug Money - Braidwood, IL on Monday, September 17, 2012 - 07:23 am:

Thanks George that is what I was looking for. This is not my engine, but a friends'. This is his third 2-piece crankshaft. Just trying to get a handle on what could be happening. The pan was rechecked after the engine was disassembled and appears to be straight on the jig. The pan is being replaced this time around "just in case". The engine is not lugged and the radii appear to be ground correctly. I will try to get some better pictures.

Thanks


Top of pagePrevious messageNext messageBottom of page Link to this message  By paul griesse--Granville,Ohio on Monday, September 17, 2012 - 09:40 am:

Third 2-piece crankshaft? Just wondering if he is using a 4-dip pan? Ball bearing 4th main? George has an excellent analysis---of course after the fact......question is what caused it to break? Paul


Top of pagePrevious messageNext messageBottom of page Link to this message  By Neil Kaminar on Monday, September 17, 2012 - 10:05 am:

Doug,

Cast iron or aluminum pistons?

Neil


Top of pagePrevious messageNext messageBottom of page Link to this message  By George_Cherry Hill NJ on Monday, September 17, 2012 - 10:30 am:

Doug...

If the pan is straight and true...

And if the line bore is 'good'...

And if the 4th main is set right...

And if the mains have the right fit...

And if his thrust bearing is not wandering back and forth by a bunch...

And if the pan ears are rigid and tight without huge deflection when the brakes are applied...

Then he should not be breaking them. Yeah, I know, too many 'if's'.

While it didn't appear to be the primary cause, is his crank grinder using a good nice radius without skips?


Top of pagePrevious messageNext messageBottom of page Link to this message  By Doug Money - Braidwood, IL on Monday, September 17, 2012 - 10:48 am:

Paul, yes 4 dip pan.
babbitt fourth main
Neil,
aluminum pistons
George, best radius I have seen.


Top of pagePrevious messageNext messageBottom of page Link to this message  By Robert Scott Owens on Monday, September 17, 2012 - 10:58 am:

George, Skips? Are you talking about the blend from the journal to the radius? Both sides of the radius? Thanks for you insight, Scott


Top of pagePrevious messageNext messageBottom of page Link to this message  By George_Cherry Hill NJ on Monday, September 17, 2012 - 11:07 am:

Scott,

I get in trouble all the time when I use jargon.

Sorry, but that's me :-)

What I mean by 'skip' is that when grinding, using a very hard dressed stone, you have to be vigilant that the ground surface does NOT have a break in the surface pattern caused by a grain that let loose and skidded and did a near microscopic gouge.

As small as this may seem, and as trivial as it may seem, when something starts to reverse bend in use, this often can be the 'trigger'.


Top of pagePrevious messageNext messageBottom of page Link to this message  By J and M Machine Co Inc on Monday, September 17, 2012 - 11:26 am:

You forgot one thing it's called "Magnafluxing"
otherwise known as crack detection.

You can ponder about the radius 4th main and 4 dip pan but if you didn't check the crank then the best radius in the world won't save you.

People have to remember these have been fatigued to death. An undersized crank to begin with then add 80-100 years of abuse.
The fine lines are cracks.

If anyone suggests ring test this crank rang like a bell in front of the Model T club. I made believers of them that night.


Top of pagePrevious messageNext messageBottom of page Link to this message  By Roger Karlsson, southern Sweden on Monday, September 17, 2012 - 01:05 pm:

I don't think it's possible to determine how fatigued a crank is until it has begun to show cracks - and then it's too late. The Model T bent hair pin style crank gets a lot of twist at certain rpms when the power pulses tends to increase each others impact by resonance - I'd say all T cranks will eventually crack (if the rest of the engine and car can take all the miles some of the outliers will hold up for), that's the sad truth. There's a reason all crank shafts for engines of similar displacement has been designed much thicker from the 20's up. With just some luck it's possible to set up a T engine just right and have years and years of trouble free driving - or if you're less lucky the magnafluxed old crank can break in a few thousand miles. You just never can tell hom much previous fatigue the 85+ year old metal has had. A new SCAT crank with 1.500" mains would be a much better - but unfortunately much more expensive insurance.

(..and I'm a poor T'er & takes my chances with an old crank too ;) )


Top of pagePrevious messageNext messageBottom of page Link to this message  By Ricks - Surf City on Monday, September 17, 2012 - 01:17 pm:

The Chevy crank of the era is 25 lb vs. 15 lb for the T crank. They don't break so much.


Top of pagePrevious messageNext messageBottom of page Link to this message  By Kohnke Rebabbitting on Monday, September 17, 2012 - 01:36 pm:

That crank was cracked when it was put in!

Mystery Over!


Top of pagePrevious messageNext messageBottom of page Link to this message  By Jerry VanOoteghem on Monday, September 17, 2012 - 02:51 pm:

Be cautious of corner radii that appear to be proper and large. If the radius does not follow seamlessly onto the journal diameter, it may as well be a square corner.



Case A shows a well blended radius that flows perfectly into the bearing journal and is 1/16".

Case B shows the same 1/16" radius. However, before a final grind pass was taken, only the outer diameter of the grinding wheel was dressed. The radius portion was skipped because it requires extra effort. The result is a "corner" where a clean tangency point should be. While at a glance there is a generous radius, closer inspection shows a definite demarcation where the journal diameter ends, and the radius begins. In my estimation, this is as bad as a square corner.

I have seen many cranks like this. Most of them broken.


Top of pagePrevious messageNext messageBottom of page Link to this message  By Michael Deichmann, Blistrup, Denmark on Monday, September 17, 2012 - 03:08 pm:

Roger, I have come to the same conclusion that it must be some sort of resonance issue. Now, could we just find out what RPM's to avoid....


Top of pagePrevious messageNext messageBottom of page Link to this message  By Roger Karlsson, southern Sweden on Monday, September 17, 2012 - 03:51 pm:

I guess the rpm's to avoid differs between T's depending on how/if they were balanced- but you can find them by observation. Tom Carnegie wrote this: "I think that high speed (assuming proper lubrication) is no real problem as long as you avoid the "thrum" speed. The "thrum" is a harmonic that all T's have at around 2000 rpm's." http://www.mtfca.com/discus/messages/257047/290670.html?1338331295

Reid Welch wrote this a dozen years ago: "On my own car the barometer of harmonic activity in the crank is my fan belt. Yet- seriously. My fan belt runs tight. It’s treated with an anti-slip compound. It runs straight and true on a ball bearing fan hub. I drive with the hood off, and I can glance at the belt while driving. At several road speeds the belt can be seen to flutter. I avoid steady driving at about 32 mph, for instance, because this is a belt fluttering speed. Close the throttle and the flutter instantly stops. Open wide, and the flutter gets worse- but only over a road speed band about 2mph wide."
http://www.antiqueautoranch.com/montana500/adrian/webinfo.html


Top of pagePrevious messageNext messageBottom of page Link to this message  By Doug Money - Braidwood, IL on Monday, September 17, 2012 - 04:35 pm:

Here are some more of the pictures. I appreciate the input. I know fatigue plays a large part in this. I like to learn what I can about it.



Top of pagePrevious messageNext messageBottom of page Link to this message  By Doug Money - Braidwood, IL on Monday, September 17, 2012 - 04:36 pm:




Top of pagePrevious messageNext messageBottom of page Link to this message  By Doug Money - Braidwood, IL on Monday, September 17, 2012 - 04:37 pm:




Top of pagePrevious messageNext messageBottom of page Link to this message  By Doug Money - Braidwood, IL on Monday, September 17, 2012 - 04:37 pm:




Top of pagePrevious messageNext messageBottom of page Link to this message  By Doug Money - Braidwood, IL on Monday, September 17, 2012 - 04:38 pm:


Top of pagePrevious messageNext messageBottom of page Link to this message  By Jerry VanOoteghem on Monday, September 17, 2012 - 04:42 pm:

The corners I speak of:



This is not a proper radius.


Top of pagePrevious messageNext messageBottom of page Link to this message  By Jerry VanOoteghem on Monday, September 17, 2012 - 04:45 pm:

Again:



This is not a radius, it's more like a 45 degree chamfer with hard edges at the journal and the throw.


Top of pagePrevious messageNext messageBottom of page Link to this message  By Dave Dufault on Monday, September 17, 2012 - 04:49 pm:

Question for Jerry.....
Broken Crank question

Dave


Top of pagePrevious messageNext messageBottom of page Link to this message  By Dave Dufault on Monday, September 17, 2012 - 04:51 pm:

Thanks Jerry - you answered it while I was composing....getting slower in my finger work!


Top of pagePrevious messageNext messageBottom of page Link to this message  By Jerry VanOoteghem on Monday, September 17, 2012 - 04:53 pm:

Yes Dave, that's a bad radius. Really, it's not a radius at all. The area between the bearing journal and the throw looks more like a straight line than a radius.


Top of pagePrevious messageNext messageBottom of page Link to this message  By Jerry VanOoteghem on Monday, September 17, 2012 - 04:54 pm:

Dave,

Looks like I just did the same thing!


Top of pagePrevious messageNext messageBottom of page Link to this message  By Jerry Ostbye on Monday, September 17, 2012 - 06:37 pm:

During the Can-Am tour this past weekend we were unfortunately plagued with 3 broken cranks. These were all beautiful cars and all of them were on level ground when they let go. Last year a friend of ours had his break and his was a new forged unit. I think they will all break eventually but " This is MY OPINION " Those who know me know what I am talking about.


Top of pagePrevious messageNext messageBottom of page Link to this message  By Cameron Whitaker on Monday, September 17, 2012 - 06:59 pm:

Did you try the ring test? :-)

Someone a while back made a good point about the ring test. Unfortunately, I can't remember who it was.

Basically, he made the point that the ring test should be used to fail a crank, not pass one. If it rings like a bell, then take it to get magnafluxed. If it just goes "thud," the crank is definitely shot and there's no reason to waste time or money getting it magnafluxed.


Top of pagePrevious messageNext messageBottom of page Link to this message  By Kohnke Rebabbitting on Monday, September 17, 2012 - 09:04 pm:

Hitting a crank to see if it is cracked, is the same thing as hitting your self in the head, with a Ball Peen Hammer to see if you need Brain Surgery!


Top of pagePrevious messageNext messageBottom of page Link to this message  By Ted Dumas on Monday, September 17, 2012 - 10:10 pm:

If when you ring a crank, it goes thud you know its bad. If it rings then you know it rings and nothing more.


Top of pagePrevious messageNext messageBottom of page Link to this message  By Val Soupios on Monday, September 17, 2012 - 10:24 pm:

Your absolutely right Ted! I use the ring test to determine if it's worth magnafluxing. About half the ones that pass the ring test fail when magnafluxed. All the ones that fail the ring test are boat anchors.


Top of pagePrevious messageNext messageBottom of page Link to this message  By Roger Karlsson, southern Sweden on Tuesday, September 18, 2012 - 01:39 am:

Jerry - one of the new forged units failed for your friend last year, you say?
That's bad - was it a SCAT crank as described here: http://www.mtfca.com/discus/messages/118802/133258.html?1270177217 ?
Please tell us more about what happened.


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