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Old 02-09-2021, 08:41 AM   #1
Bob Bidonde
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Default Fatigue Cracks In Model "A" Parts

I am making a presentation about parts in the Model "A" & "AA" that are prone to fatigue cracking. So I am asking for pictures you may have of cracked Model "A" & "AA" parts. Please post them here. Here's an example of a fatigue crack:


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File Type: jpg Rear Axle Fatigue Failure 221kb.jpg (33.3 KB, 157 views)
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Old 02-09-2021, 11:04 AM   #2
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Default Re: Fatigue Cracks In Model "A" Parts

Probably the most frequent crack is on the front fenders. On the top and traveling outward to the edge bead. It would be interesting to put a set of strain gages on them.

I’m sure the engine splash pans would fit your category. Right where they attach to the frame and pan rail.

The original fan blade was probably highly stressed.

Good luck. I have no pictures.
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Old 02-09-2021, 11:10 AM   #3
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Default Re: Fatigue Cracks In Model "A" Parts

This is not fatigue, but common failures.

Upper distributor brg.

The tapered connection of the fan pulley to the water pump shaft. If there is any mismatch between the two tapers, the joint will pound itself to failure.
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Old 02-09-2021, 11:22 AM   #4
Bob C
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Default Re: Fatigue Cracks In Model "A" Parts

Here's a common one. No picture but the steering column by the spark and
throttle rods.
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File Type: jpg DCP_0565.jpg (43.0 KB, 83 views)

Last edited by Bob C; 02-09-2021 at 11:27 AM.
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Old 02-09-2021, 12:41 PM   #5
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Default Re: Fatigue Cracks In Model "A" Parts

Cracks in the flywheel housing when the front of the engine has been jacked up to change the pulley . If two of the rear engine (one each side) are not removed the flywheel housing holds the front end weight of the car .

John in cold Suffolk County England .
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Old 02-09-2021, 01:02 PM   #6
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Default Re: Fatigue Cracks In Model "A" Parts

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Quote:
Originally Posted by john charlton View Post
Cracks in the flywheel housing when the front of the engine has been jacked up to change the pulley . If two of the rear engine (one each side) are not removed the flywheel housing holds the front end weight of the car .

John in cold Suffolk County England .
I don't think this qualifies as fatigue per the original question. Fatigue cracks result from cyclic loading that causes progressive structural damage, first hardening the material, then forming a crack, and eventually failing.
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Old 02-09-2021, 01:10 PM   #7
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Default Re: Fatigue Cracks In Model "A" Parts

How about the clutch arm. Will it qualify to what you are asking?

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Old 02-09-2021, 01:25 PM   #8
Keith True
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Default Re: Fatigue Cracks In Model "A" Parts

Front hubs.Not the solid forged ones,but what I call pressed tin ones.(they're really not) They are the ones that have a cup in them,that you can see after you remove the drum.They will flex and break where the face folds down over to form the cup.Looks like it was cut with a lathe,except for the last little section that finally gives out.
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Old 02-09-2021, 02:05 PM   #9
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Default Re: Fatigue Cracks In Model "A" Parts

Going back to flywheel cracks I do think that fatigue cracks can occur in a flywheel housing . The torque tube pushes the car along which is transmitted to the transmission then to the engine . The rear motor mounts push the car along this thrust through the relatively thin cast iron flywheel housing which must flex slightly thousands of times in service . Ford beefed up the flywheel housing several times with extra webbs I dont think this was done to avoid damage when the front of the engine was jacked . Pullies and front motor mounts are changed many times over a cars life and if this is done over again it could be said a fatigue crack would eventually occur .IMHO . The rear spring does not add much forward push as fore and aft it is too flexible to input much drive .

John in still very cold Suffolk County England .
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Old 02-09-2021, 02:23 PM   #10
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Default Re: Fatigue Cracks In Model "A" Parts

Crank shafts have been known to break. I VERY narrowly avoided having it happen when a crack was found through #3 big end journal when he motor was being inspected in preparation for a long and hard drive. I was told I wouldn't have gone another 100 miles so you might say I got the best out of it. It was about 85 years old at the time.
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Old 02-09-2021, 02:27 PM   #11
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Default Re: Fatigue Cracks In Model "A" Parts

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Originally Posted by alexiskai View Post
I don't think this qualifies as fatigue per the original question. Fatigue cracks result from cyclic loading that causes progressive structural damage, first hardening the material, then forming a crack, and eventually failing.
Colin, I think John has a point. IMO the fatigue cracks in a flywheel housing DO come from cyclic loading from the rear axle transmitting forward motion thru the torque tube, thru the transmission and clutch housing, and ultimately causing the flywheel housing to flex. As the vehicle encounters pot holes, railroad tracks, and bumps during regular driving, the load is varying from positive to neutral pressure constantly.



Bob, I have a Kwik-Way wet Magnaflux machine that uses a fluorescent metallic fluid to seep into cracks of a magnetically charged component. We then use a Blacklight to find/see the cracks. Unfortunately these cracks are often difficult to see without the Blacklight, and are even more difficult to photograph. I will tell you that WAY more components fail the crack-checking with a machine then found by a naked eye of a Restorer. While I have never heard of a Model-A spindle breaking into two pieces due to a fatigue crack, it does pose the question that if a Restorer did know their front spindle has a fatigue crack (-as verified by Magnaflux or ??), would they still use it on their car??
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Old 02-09-2021, 02:41 PM   #12
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Default Re: Fatigue Cracks In Model "A" Parts

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Colin, I think John has a point. IMO the fatigue cracks in a flywheel housing DO come from cyclic loading from the rear axle transmitting forward motion thru the torque tube, thru the transmission and clutch housing, and ultimately causing the flywheel housing to flex. As the vehicle encounters pot holes, railroad tracks, and bumps during regular driving, the load is varying from positive to neutral pressure constantly.
I agree that a flywheel housing could crack from fatigue – my point was just that cracks which are caused by the unique strain of jacking up the front of the engine aren't fatigue. Similarly, if you crack a cast iron piece by over-torquing its fasteners, or break a connecting rod due to incorrect assembly, that's not fatigue.
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Old 02-09-2021, 02:54 PM   #13
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Default Re: Fatigue Cracks In Model "A" Parts

That clutch arm is a good one, and we have all replaced cracked engine mounts. Both of those are fatigue.
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Old 02-09-2021, 03:10 PM   #14
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Default Re: Fatigue Cracks In Model "A" Parts

Here are two previous posts with photos of cracks in bell housings:
https://www.fordbarn.com/forum/showp...93&postcount=8
https://www.fordbarn.com/forum/showp...2&postcount=10
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Old 02-09-2021, 03:14 PM   #15
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Default Re: Fatigue Cracks In Model "A" Parts

Bob, this is a picture of a cracked radiator neck from the top tank. You can see the daylight shining through the crack. Since this is under the radiator shell, it makes it hard to spot.
IMG_1700.jpg
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Old 02-09-2021, 03:46 PM   #16
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Default Re: Fatigue Cracks In Model "A" Parts

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Bob, this is a picture of a cracked radiator neck from the top tank. You can see the daylight shining through the crack. Since this is under the radiator shell, it makes it hard to spot.
Attachment 455318
I also had a radiator neck pop off one time on a tour. It was a quick and easy fix later to re-solder the original neck back on.

I had a discussion once with an owner of a Model A radiator shop who also told me that some of the reproduction radiator shells did not have an radiator neck opening large enough to compensate for the accessory radiator caps like the twist open motometers and quails being sold. When the car owner used the allen wrench to fasten the lower part of the cap into the radiator neck he would put a lot of stress pulling up on it just like he was using a gear puller... This radiator shop owner tooled up a slightly longer radiator neck for his Model A radiators to compensate for this and stopping later complaints of the necks cracking..
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Old 02-09-2021, 03:53 PM   #17
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Default Re: Fatigue Cracks In Model "A" Parts

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How about the clutch arm. Will it qualify to what you are asking?

This cracking of the original clutch arm has been a ongoing issue with members of my local Model A club. I believe 3 occurances happened in just one tour season alone. Many of the members have now swapped the original clutch lever for a new reproduction ones as a preventive measure. Good idea as when this part fails, you are dead in the water and will need a tow truck ride home....
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Old 02-09-2021, 03:57 PM   #18
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Default Re: Fatigue Cracks In Model "A" Parts

I have seen on my Model A's a broken rear axle and a broken crankshaft that was from fatigue cracks or possibly original flaws in their manufacturing. Funny it only took 85 years of use for these breaks to occur....
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Old 02-09-2021, 04:26 PM   #19
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Default Re: Fatigue Cracks In Model "A" Parts

Firewall cracks around the two hood rod brackets. Ford fixed this some time in 1931 by spotwelding a doubler on the back side of the firewall.
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Old 02-09-2021, 04:39 PM   #20
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Default Re: Fatigue Cracks In Model "A" Parts

No photos but back in 72 I had my gear shift snap off just a few inches above the transmission, where it curves. Just as I shifted into second gear.
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