WHY DO T CRANKS BREAK BEHIND #1 ROD?

[speedytinc]

Its generally understood that a crank that breaks around or behind #3 is from a crank case misalignment. Correct?

Why do they break behind #1 rod throw?

I have broken 3 cranks in my T career. All broke behind #1
First was from a "professionally" rebuilt motor. The radius's were ground near square. Break started in the sharp corner. Obvious issue.
Second was a mint std/std shermike crank. They all break. I expected it to break, but it was so nice, I took the gamble. Metallurgy issue?
Last one was a std/std original? 14 crank. Wrist pins were a bit tight. Not seized, but stiff. Could this be the cause or a major factor??

Anybody have tight wrist pin issues with their broken crank?
Is it all coincidental & mostly a result of age & metal fatigue?
Any other educated theories out there?

[Jerry VanOoteghem]

I don't believe there is a general rule with crank breakage. There can be many causes, with the A#1 cause being metal fatigue. It sure doesn't help matters however when there is no radius on bearing journals, bent pans, high rpms, broken timing gears, misaligned main bearings and bad luck.

[Kevin Pharis]

Wimpy crank, wimpy rods, and high reciprocating mass paired with no harmonic flywheel means that the front end of the crank is allowed to change speed as the load changes throughout each revolution. The further the load is from the flywheel, the more deflection and stress the crank will encounter. Where will it eventually break…? At it’s most convenient stress riser!

[Norman Kling]

One possible cause would be sag of the 4 th main at the rear of the transmission. caused by a bent crankcase. This will put pressure on the center main of the engine causing wear at the top pushing the crank up into the block. When you try to adjust the center main to keep it from knocking as you drive along, it also forces the crankshaft to bend upward. at that point. So the front main is holding the crank in one position and the second main is bending the crank. The weakest point would be between number one rod and number 2 rod.
Norm

[TrentB]

First of all, I agree with Jerry, metal fatigue is a major cause of Model T crank failure. But what contributes to metal fatigue? Here is my list of causes of metal fatigue in Model T crankshafts:
1. Lugging the motor. Keeping the rpm’s down when driving can cause the crank to lug causing metal fatigue and failure. One of the reasons I prefer 4-1 rear axle gears is because it keeps the rpm’s up and reduces lugging of the motor.
2. Not having the four main bearings, three in the block and one at the end of the transmission, perfectly straight and in alignment. If the bearings are not perfectly aligned the crank will flex as it rotates causing metal fatigue and failure. Taking shims out of the center mail bearing to take up wear is a frequent cause of misalignment and crankshaft failure. Vanadium steel was great stuff for the time, and when new it could be twisted like a pretzel without breaking, but if vanadium steel is subject to long term flexing it will fatigue and break.
3. I suspect, but cannot prove, that some crankshafts are metallurgically inferior to others. I have seen more two-piece Cleveland Hardware crankshafts than any other manufacturer. 26-27 EE crankshafts seem to be the best.
4. Others can add their reasons for crankshaft failure here:

Respectfully Submitted,

Trent Boggess

[Dan McEachern]

THINGS HATE PEOPLE~

[TXGOAT2]

High hours, abuse, torsional vibration, poor fitting, loose/mis-aligned rods. Shot peening a crank might help prevent breakage.

[KWTownsend]

John,
You are one up on me. This is my second. I have no desire to tie with you!

There are two types of Model T drivers:
1) Those who have broken a crankshaft.
2) Those who will brake a crankshaft.

Winter project...

: ^ (

Keith

[George Mills]

I'm actually going to agree with Norman on this...

(No, please don't send me your dead cranks...we tried that one time, they multiplied faster than rabbits and all had the same problems described here).

Look at your break and describe it...the reason for the break is actually visual in the surface of the break! The shadows show an S pattern? it failed in total torsion overload-cause to be determined.

The break shows show a clam shell pattern for about 2/3rd's and a pure cleave for the last 1/3rd? Shaft failed in bending fatigue and the fist place the outer ring crosses the OD? That was the starting point/nick. See two clam shell patterns, maybe in two different directions even? Ut-oh, it started due to one cause, finished due to a second cause...all in bending

Doesn't answer the 'how' but shows the 'why'. Any mixture of the above is compound action and once that starts it is anyones guess for how fast. The reason there is a final 1/3rd 'cleave'. is that whether they planned it or not, the Boyz wound up with a net 3 to 1 safety factor and at the 1/3 surface area remaining the 22HP is not at the yield point, it went right to exceeding tensile in one quick snap.

On another note, just the slightest of anything at a corner and all bets are off on 'slow road to failure'. Thats like using a sledge in place of a tack hammer. Any radius at all drops that phenom dramatically.

I'm of the opinion that most failures ARE originating from a poor 4th mounting. If the 4th wobbles and deflects with each rev...the crank itself runs like a piece of sprung spaghetti. I'm not sure that even modern 4140 billeted can last long running that way. SA-649 was designed specifically for reversing and oscillating loads that can have a .035 center deflection for billions of cycles if tempered out correctly. Problem is, it was a boutique steel, and no one in USA seems to want to induction melt it from 4140 anymore since all of the original applications are now fulfilled with a European grade (I think EN-19?) Paul Vitko of Washington and someone else out west (name escapes me) mounted dial indicators on the 'tail' and went for rides on airport runways with on guy driving, other guy near upside down reading gauge. The numbers were frightening, cause just on the other side you knew the reverse was also happening

[bdtutton]

How often does it damage and/or destroy the block when a crank breaks?? My original to the car engine was built in October of 1913 and runs well, but I sometimes think about replacing it with a mid 20s engine to get an electric start and protection against ruining the original engine.

[Norman Kling]

I have seen a block on which the web over the third main had been cracked or broken and had been welded up. The engine was still running and we thought when the big bang came that the crank had broken. Unfortunately, the driver lost his brakes when coming up to a signal and he hit the reverse pedal to stop the car. Then the reverse drum shattered. We replaced the transmission and saved the engine which still ran fine!
Norm

[Russ T Fender]

The original crank on my '10 broke right behind #1 which is no surprise but on inspection I found that there was a void, almost like an air bubble, that had been there from day one. What amazed me was that crank lasted as long as it did with that latent defect. Fortunately there was no damage to the open valve block and I replaced it with an EE crank as Skat cranks had not yet shown up on the scene. I must admit that I am a little nervous now every time I take the '10 out and I am seriously considering running a later engine or better yet a an open valve knock off.

[Kerry]

Lots of reasons listed but the one from the very beginning of production, Ford put out a film clip back in the day of how he made the cranks, near white hot lump of steel and bang a huge press like weight on it in a mold to shape a crank, consensus was many years ago that the crank had faults in it from the day it left the factory. Hess the old saying of, it's not if the crank breaks, but when.

[Dan McEachern]

Just more fuel for the fire. We had two crankshafts on two different cars break in #3 Rod journal in the same place on the same 3 day tour a few weeks ago............the angle suggests a torsional failure but........... both engines would still run due to the break being held together by the connecting rod. Just a little rattle........

r

un

[Kevin Pharis]

^^^^^^^^
That crank looks familiar…

A new Skat crank and 1 rod later… it’s back on the road!

[TXGOAT2]

The 'bubble" inclusion was called a "cold shut", I think.

[RajoRacer]

Then there was this one - 5 y.o. rebuild - low mileage speedster.

[Jugster]

I'm not a physicist, not a metalurgist and not a mechanic. When I hear people using terms like "harmonic balance," I know I'm out of my depth. From the point of view of someone like myself, knowing what to do about the problem is more important than attempting to understand the esoteric, scientific reasons why certain types of molocules decide to stop holding hands.

I can understand this:
The throttle is the fracture control. The closer the tip of the throttle handle is to the floorboards, the more likely it is that a crankshaft breakage may occur. This effect is multiplied when climbing a hill in high-gear. So I treat the throttle like a loaded bazooka. I accelerate gently, go easy on the throttle after the up-shift and avoid hills whenever possible. Though of only average intelligence, I don't suppose a quantum physicist could do too much better than that behind the wheel.

[TXGOAT2]

Don't lug the engine in any gear. Don't rev it over 2,000 RPM. Less is better. Don't drive the car for extended periods at speeds where the engine vibrates more. Don't use thick oil. Don't drive the car with loose bearings. Keep the engine tuned up and running smoothly. Learn to drive smoothly, without lurching shifts, lugging, or over-revving.

[Original Smith]

I wouldn't consider using an early crank. Use a late one, or preferably an EE. I broke one a long time ago, early, and have had good luck with the late one.

[Jim Eubanks]

My experience was the forth main, I had a ball bearing and after two broken cranks went back to a babbit forth main and never had another problem

[Allan]

The post about the repaired block and the last one with the broken rear web are indicative of a particular problem, especially on early blocks. The land on which the third main bearing bolt heads sit is machined flat to take the bolt heads, but this machining creates a perfect sharp stress riser between the bolt head surface and the vertical edge of the block. It is not uncommon for the back web in the block to break out. On occasions this break is attributed to a broken crankshaft doing the damage. This is not necessarily the case. That web letting go takes the crankshaft with it.

I have seen a 19 12 block which was removed from service before it let go. The crack emanated from the bolt land down either side of the web, but for some reason it was discovered before it broke out. I had that block welded and it was also returned to service.

A 1912 mother-in-law roadster in our club was not so fortunate.

A 1923 engine came to me with a broken out rear web and crankshaft. On inspection, the crack starting at the bolt land had clearly been "working", as the break surface was polished. Only the last little bit of the final breakout was a clean break.

I never begin work on a block now unless it has been crack tested, with particular attention to the rear main web.

If you bust out the rear web, check to see if yours might also be the precursor to a broken crankshaft.

Allan from down under.

[TXGOAT2]

Excellent advice.
Castings don't like sharp inside corners.

[Erik Barrett]

They break for many reasons. They are all past their realistic life expectancy. Then many of them were put back into service without magnafluxing and proper regrinding, particularly the fillet radii. Every one of them is going to break sooner or later. I am putting more Scat cranks in than properly vetted and ground late style original and EE cranks these days. It’s getting nearly impossible to get core T cranks that I can send to my grinder in large batches that give me a better deal. I may have sent him my last batch of 25 a year ago and he was planning to retire even then.

[Gen3AntiqueAuto]

#1 reason - misalignment. When it's due to not aligning the transmission correctly, harmonics come into play and travel the length of the crank. It's possible that spot is just where the sounds matched the metal. It can also be the 2nd main bending the crank.

[J1MGOLDEN]

There may be a connection with the fact that Rod #2 gets less lubrication that the others.

I have had three #2 rods begin making a lot of noise before anything breaks.

When the engine and then the crankshaft is removed, it was still saved by grinding and polishing the #2 surface area.