How's about an HONEST survey of folks on the forum here or if you know of someone that had the misfortune of experiencing this disaster, perhaps post answers to the following questions:
1. Was the crankshaft broken on a tired, old engine or a recent rebuild ?
2. What crankshaft - early diamond web, straight web ('26-'27), Model A - shortened or full length or other accessory crankshaft ?
3. What was the car doing when it broke - accelerating, braking or cruising ?
4. Do you have direct knowledge of the crankcase being checked on the proper equipment designated for the task ?
5. Was the broken crank engine utilizing an original equipment Babbitt ball cap or an accessory "ball bearing" ball cap ?
Thought the information might be useful to others contemplating a rebuild in the future.
Here's my sad story:
1. Recent rebuilt engine.
2. Was an early '12 crank.
3. Just got back from a long run on Kanab tour and crank broke in town doing about 15 to 20 mph.
4. Crank was checked and balanced at machine shop,
5. Babbitt ball cap.
Damaged the rear of block.
Installed new Bill Dubats counter balanced one.
Friends '23 touring. 2010
Rebuild new Babbitt 2 years old little time on engine
'23 crank. Magnafluxed. .020 mains and journals
Broke on slow high gear 10mph trip back to Hershey space after trip to the showers 4 large adults aboard
Pan checked on jig and engine build by owner who is practiced rebuilder of T's and A's
Babbitt ball cap,
1. engine was rebuilt in 1955 broke 2013, 2. it was the original 1912 db crank 3. just headed out on a tour 3 blocks from home 4. engine was rebuilt before the car was purchased. 5. original equipment New scat crank on the way it is a work in process. no damage other than the crank which did last 101 years 1 rebuild and 53 years of enjoyment.
My Speedster crankshaft broke cruising about 30 or 35 mph. We had passed several Model A's the day before.
1920 engine, maybe 2000 miles after rebuild.
No special attention to alignment when rebuilt.
Babbitt ball cap.
I fitted another crankshaft to that block and rods and have driven another 9000 mile with no trouble.
1 Engine getting tired.
2 Stock 14 crank.
3 On tour running hard about 35-40.
4 No idea when rebuilt but found a Bad Ball Bearing Ball Cap.
5 Total rebuild Ballanced EE crank and Flywheel.
Dammage 1 or 2 cyl bores.Bud.
1910 original crank, rebuilt about 8,000 miles prior, pan straightened when rebuilt, babbitt 4th main. Pulled up on the crank to start and heard a bang, shut it right down and pulled to engine. Broke right between. # 1 & # 2.
1 Engine had 5 years and several thousand miles on it with Rajo 4 valve head.
2 Stock late but not EE crank.
3 Flat road cruising at about 50 in overdrive (probably 1600 RPM). about 20 miles from the end of a 3 day 600 mile speedster tour.
4 No special equipment checking. Engine set vertical and 4th main fit with no restriction or adjustment required.
5 Modern 4th main.
Crank broke between 1st & 2nd rod journals. No damage to block or babbitt. Crank, flywheel and trans drums had been statically balanced.
Second Time -
1 engine had another 6 or 7 years of service, definitely broken in but not tired. Now had a type T Fronty head.
2 Another late but not EE crank.
3 Loafing along about 30 in direct.
4 No special alignment tools/checking. Set as above.
5 Same modern 4th main.
This time the rear flange broke off the crank with some damage to the thrust surface on the 3rd main but no damage to the block. Crank, flywheel and trans drums had been statically balanced.
That motor now has a shortened A crank so hopefully it won't be doing this again (soon).
I am a two time looser. First crank was not a 26-7 double e. It was in a good condition engine and broke when accellerating up a hill in low ruckstell. Engine had a ball bearing 4th main.
Same engine, New Zealand crank. Broke while at slow rpm in a Christmas parade. Same ball bearing 4th main.
Threw ball bearing junk out and put a double E crank in and is running fine.
After ten years of service the one in my 14 broke. I was slowing down to go around a corner. It was the original engine so I have no idea what was ever done to it.
Gene, what damage did the broken crank do to your block?
I have seen and heard of a number of early blocks where the broken crank took out the rear main bearing web in the block..... Or did it?
When the same thing happened in 23 block it was quite clear that the block had been cracked in the webs at the rear and the cracks had been working, as they were polished. When the block let go, the crank went with it.
I bought a 12 block from the West Australian Veteran Car Club parts store and when it was chemically cleaned for re-metalling, serious cracks were evident in the rear web. If that block was used just a bit longer, the same would have happened.
I would be interested to know how many similar breaks have occurred. I am of the opinion that many broken cranks taking the rear web with them are in fact quite the reverse. The block lets go and the crank goes with it.
Just for interest and further discussion.
Allan from down under.
Good thread. Hope Steve is organizing the data. From cursory look, I don't see any real pattern. One question I didn't notice is whether there were any aftermarket performance upgrades. High compression heads or piston? I did see one Rajo.
Thanks Guys ! I believe we'll get some great info regarding this subject. I think we all (me included) are guilty of driving these ol' girls a bit harder than what their original designed task was meant for. Obviously, we have better roads nowadays but after 90 to 100 years of "who the heck knows what conditions these cars were subjected (extensive use of low band at high RPM) to and through mud, snow, etc., I feel fortunate we have the resources, including this forum, available to keep these cars running.
Very good point, Hal - let's include the use of stock or slightly milled heads to Hi-Compression, steel or aluminum and overheads.
I move to include timing gears. Some speculate that broken cranks might be due to stripping the teeth on a fiber timing gear.
Iron or aluminum pistons....
Sorry Steve. Didn't mean to mess up the works.
1. Engine rebuilt at least 20 years previous with many thousands of miles. Heavy 1912 rods, Ford Y block aluminum pistons
2. Dodge Brothers original 1912 crank
3.Idling with the parking brake set
4.Checked good on disassembly
5.Babbit still in perfect codition
Your crankshaft will break some day. It does not matter what you do they all break eventually.
On both of my breakages - typical flat top aluminum pistons and timing gears were fine. Both the 4 valve Rajo and "T" Fronty are relatively low compression heads although the do breathe far better than a stock flathead T.
I had run both engines fairly vigorously but had not been abusing them at or shortly before the time of failure. I chalked the failures of to the use and abuse they had endured for 80+ years. I don't look forward to breaking a crank again but consider that it's always a possibility for a car that gets driven. Just one of the reasons I have AAA.
Wow. Every which way and at any speed. Actually no common denominator.
I haven't seen anybody mention transmission alignment.
My EE crank broke when dropped. It was not in an engine and it was no longer in my hand either! Broke at #2 journal and had fibers of band material in the crack.
I bought my engine from Don Bell and as I understand it was running a saw mill in Oregon someplace when he bought it. The engine actually did run, it's just that my dad and I thought that since it wasn't in the car we might as well rebuild it.
I didn't bother to put the old crank in. Had Egge's Machine Shop in L.A. do some fitting and pour babbit for a Model A crank and put in Aluminum pistons as well. Also put in alloy valve seats and guides. At the time (78') unleaded was not standard, but I was pretty sure it would be, so, I opted to get the engine ready for it anyway to avoid having to crack it open and do it later.
Fairly new rebuild
On the Matches Trace Parkway, after a pit stop.
Restarting the engine was all it took.
1925 Fordor. Had to push it onto the trouble trailer.
Was a long trip back to Sacramento.
I now have an A crank with inserted, drilled mains.
1. Tired, old engine.
2. Early diamond web.
3. What was the car doing when it broke? - Cruising along about 35mph, along a meandering river.
4. No idea if crankcase had been checked previously.
5. The broken crank used an original equipment Babbitt ball cap.
Rebuilt engine: Straightened pan, installed aluminum pistons, Chaffin's "touring cam," Z head, Ball bearing fourth main.
Runs like a top!
I am a firm believer that an old, tired bent pan is a crankshaft's worst enemy. Don't bother to do a rebuild unless you straighten the pan!
: ^ )
I broke an original '13 diamond crank doing about 50 mph years ago in Warford overdrive. It was the crank that was in my car when I acquired the car in 1961. The pan was straightened, and had a bronze bushed rear main. I now have a late crank in it, with the same 4th main. It has gone many thousands of miles since then with no crankshaft problems. The crank broke on a slant through #3 connecting rod.
Opp's i did not mention while on teardown i could find no fault except the Failed ball bearin ball cap!! Of course babbitt was used this time!! Bud.
In the 25 years I have been involved with the Tulsa Club, I know of only two cranks that have broke.
One was a diamond crank a number of years back that was in a fairly recent rebuild. Flywheel, rods, pistons, transmission drums balanced, balanced,transmission was aligned, it was a group project. On a tour the owner though he was hearing something funny and we had pulled in to a pit stop, stop the car and was looking under the hood. Had started it up a couple of times and couldn't hear anything out of the ordinary. He asked me to drive the car, got in and started it and the crank gave way on the start up. Bet he will not asked me to drive his car. LOL long and the short of it, turns out when he had the crank shaft ground he opted not to have it mag check so we don't know for sure but guess it may have been cracked on the rebuild. This was a diamond crank, early/
The second one just gave way, had a lot of miles on it, was a later crank shaft, again was a balanced engine and transmission in alignment. Crank had been mag check before grinding Our crankshaft grinder knows about the radius requirements.
Both ran babbitt fourth mains, both are Model T guys, so I don't feel it was the owner fault.
Never real came up with an explanation for the second crank that broke. Some times bad things just happen to good people.
Most of the cranks I get are cracked, they are old and wore out. I have a couple of club members that have cranks ground ,040” and 050” under and are drivers. The one that is .050” has been running over 30 years and the owner just wanted to freshen up the engine. We found the crank was still good, mag check OK and put the engine back together. Do I recommend turning a crank that far under, no, but I have yet to see in writing were the line got drawn at .030”. Just food for thought.
Most of the crankshafts I fine to be broke are in the web not on the rod throw and can be any where on the crankshaft. No real pattern to where they will crack.
Another observation is the third main will have more wear. Before tear down I will check the run out on the fourth main, it will have a lot of run out in some cases over .030” and will find the transmission drums are way out of balance along with the main shaft having run out. I feel a lot of crankshaft failures are due to the transmission alignment and balance.
1. The crankshaft in our 13 touring broke while owned by a previous owner. The rear main web was broke out. A local friend had the same thing happen to his 12 touring (Correct Early Block). Both blocks were repaired by having the web brazed/ark welded back in place.
5. Both were using Babbitt in 4th main.
Steve, none of us know what our cars were subjected to before being adopted in our families.
One thing we do know about driving with a stock crankshaft......It is not if the crankshaft will break......it is when it will break that we do not know. The bottom line cause is Ford was too cheap to put a strong crankshaft in his T's....he corrected that with the model A.
Les - Just personal opinion from what I have learned over the years, mostly from this forum, and in this case, Paul Vitko's research & testing and the information he's posted on the forum in the past:
I agree with what you said about Ford correcting the problem by putting a strong crankshaft in the Model A. However, I believe Ford recognized the weak "T" crankshaft AND a weak stamping for a crankcase that flexes, and partially acknowledge these problems and attempted a "band-aid" fix by bolting the top of the hogshead to the back of the engine block in the "new improved '26-'27 Model T. I believe that one huge factor in broken "T" crankshafts is the fact that the Model "T" powerplant (engine/transmission unit) is only as rigid as the stamped sheet metal crankcase that allows the powerplant unit to "flex" which adds a lot of strain on an already inadequate crankshaft. In other words, the two bolts were Fords acknowledgement that there was another problem besides the too weak crankshaft and those two bolts were a "band-aid" that "helped" in the '26-'27, but did not solve the weak crankshaft problem, but only prolonged the inevitable.
1. Original part put into a new rebuild.
2. Reground original pre 1926 crankshaft
3. What was the car doing when it broke - changing gear from bottom to top.
4. Do you have direct knowledge of the crankcase being checked on the proper equipment designated for the task ? Yes, checked with a spirit level and straight edges.(toolmaker by trade, it was straight)
5. Original white metal type 4th main.
There was a vertical a crack on one side of the rear main boss. I almost missed it but you could see that the bearings didn't line up when viewing from the rear. The damage was caused when the broken front rotated around and hit the back piece at an angle or on one side.
I see quite a few others had similar damage. I wonder if the early blocks might be weaker there?
Gene, that was my thought. I know of 3 early blocks which have had broken out rear webs. It was not until the 23 model block came up, with part of the web still in place, but showing evidence of 'working' when the last piece was broken out, that I questioned the usual wisdom that the crankshaft break took out the web.
Just for interest.
Allan from down under.
Years weren't listed in all cases, but I counted:
1914 & earlier: 10
1915 & later: 7
Considering how many more later cars there are, it would seem that the early ones are much more likely to break based on what has been reported so far. Other possible factors that I don't think are as good an explanation as the year of manufacture are: 1) a higher percentage of people with early cars post here, 2) the older cars all have more hours than the later cars, and 3) early brass cars get driven more.
My car was was a Dalgety assembled 1925.
Just for the record, I was recently informed by Adam Doleshal, that he is rebabitting 4th main ball caps.
1. Was the crankshaft broken on a tired, old engine or a recent rebuild ? Partial rebuild about 7 years ago, 26 engine new alum pistons, magna-fluxed crank, original mains
2. What crankshaft - early diamond web, straight web ('26-'27), Model A - shortened or full length or other accessory crankshaft ? Early diamond web
3. What was the car doing when it broke - accelerating, braking or cruising ? Climbing a hill in high about 20mph
4. Do you have direct knowledge of the crankcase being checked on the proper equipment designated for the task ? The crankcase was not checked for straightness.
5. Was the broken crank engine utilizing an original equipment Babbitt ball cap or an accessory "ball bearing" ball cap ? Original babbitted 4th main
I put a few thousand miles on the car since the partial rebuild then bang. No damage to block
I am rebuilding with a Scat crank
Thought the information might be useful to others contemplating a rebuild in the future.
I was driving a friends '23 fordor at 30 MPH when the crank broke between 1 & 2.
We never knew the history of the engine.
I have heard very experienced model T guys agree that more cranks broke at slow speed than at high speed.
They often crack at low speed and hang on a while & break later when at higher speed.
Wow - what a great outpouring of information !!!
Another variable that was brought to my attention and I consider a genuinely valid question is;
How many of these broken cranks had either a supported auxilary transmission such as an original Warford, Chicago, etc. or any unsupported auxilary unit like the new Warford ???
Mine broke in the Special while climibing a slight hill on our trip to Bonneville last summer. Barely put my foot into and bang! Shut the motor down.
My engine is 1917 block. Broke between 1&2 . Was recently rebuilt but I didn't magnaflux the crank. We used a roller bearing 4 Th. main. I also run a Warford in her that is supported with a custom built crossmember. Did not check the pan before but checked it this time. Pan is straight as best we can tell.
You stated "Your crankshaft will break some day. It does not matter what you do they all break eventually".
Perhaps there might be some truth to your statement BUT I have in my possession, my Grandfather's 1924 TT C-Cab Express that he purchased new here in Seattle, owned & operated the M & M Grocery in Seattle well after WWII for deliveries and used it as their only mode of transportation daily until 1958. There are stories of my Gramps being seen driving up some of the hills of downtown Seattle in reverse ! This truck was equipped with a cast iron, three speed Warford, auxiliary brakes and a Atwater-Kent distributor - AND it has it's original engine & crankshaft as I have most all of the records associated with this truck ! I replaced the driver's side short running board as it had the "Ford" script completely worn off and you could see the ground through it - we have no idea how many miles is on this old truck. Maybe, someday I'll be getting a tow home.
I've used a 26/27 block & trans cover with a 4 dip pan on the speedster. A Chicago trans with no rear support bracket.
Hmmmmm,....maybe that's why they call him "Walt (let it all hang out) Berdan"!
I wonder if it's not just a matter of a manufacturing defect that creates a stress concentration. Then it finally fails. Believe it or not, I put the crank back in my truck engine with a known crack.......OK, now that you guy's have picked your jaw up off the floor, it is a small longitudinal crack forward of the front main. It has probably been there since the day it was forged. If it were to fail, I'll loose the pulley, but I doubt it's going to fail there. There's no load on it. That same flaw between journals might prove to be catastrophic.
Thanks Guys - let's keep the information coming. If nothing else, one might be assisted in determining the proper course to take when considering a "rebuild".
I requested an "Honest" answer to my questions - not any opinions - thank you.
Deductive reasoning concludes that after nearly 100 years of "who knows what" kind of stresses were placed upon ANY Model T that still survives with the crankshaft being the backbone of the operation - perhaps a new, modern replacement crankshaft is the way to go - maybe - maybe not - thus my reason for taking this survey.
Fortunately, AND I am knocking on wood, with 5 Model T's in the stable, my day may be coming BUT until then, I am either one lucky SOB or my Model T Guardian Angel is watching over my A-- !
In my belief that truing up the transmission and balancing the components will do the most in extending the original crankshaft limited life. I have balanced and trued up 5 or more transmissions and am amazed on how much run the transmission shafts that I have checked have. I have read that some new engines that vibrated badly were later found to have "Bent" transmission shafts.
Just truing up and balancing the transmission can significantly reduce the internal stress on the crankshaft. I noticed a "BIG" difference in vibration with our 13 touring. I started with checking the outside crankshaft flange face ending with the 4th main. I also added a modified ball bearing 4th main that allows the out put shaft to slide in and out the inside bearing race. It is important that the out put shaft be able to move as the transmission expands and contracts. Provided the out put shaft can move in and out, I see no reason why a ball bearing 4th main will cause more crankshaft failures compared to the original Babbitt bearing. I am still running a early diamond shaped crankshaft with these modifications.
Just my thoughts....you may or may not agree.
Forgot to add that Harold brought up a good point and whatever happened to Paul ?
As with anything else you have to know what you're reading to understand what you see.
I would highly recommend to anyone with an old car to get the parts magnafluxed.
I saw above where people mentioned that they had the cranks magnafluxed and they still broke.
Well it depends on how experienced they were and if they understood what they were looking at.
I understand that magnaflux can't pick up internal cracks however even an insignificant crack on a crank that showed up would be a red flag.
In these two pictures shows the same crank with a crack on either side of the center main.
Often times the crack is less than 2mm less than 1/8" but if it's on the crank then I wouldn't use it as it's going to grow.As seen in the picture with the three small cracks.
This scuttlebutt about the EE cranks well they crack also.
My 13 suffered a broken shaft about 100 miles after rebuild -it was fitted with one of the early cranks manufactured locally (New Zealand) Apparently there was minimal radius where the web meets the shaft resulting in an inherently weak shaft. This all happened before I brought the car However the tooling was changed and my car was fitted with one of the new crankshafts. Still not convinced they are that flash a job but so far is going all right and not really prepared to strip everything down to replace the crank shaft until I need to -Karl
1. Crankshaft was in an original engine.
2. 1926 crankshaft (just after the 1925-26 changeover).
3. Car was cruising downhill at about 65km/h.
4. Engine had never been out of the car since new.
5. Original babbit ball cap.
Magnafluxed 1927 EE went in as a replacement.
EE crank, machinist warned me the journals had been cut too square in a prior rebuild (he didn't turn or grind the crank) and would likely break because of insufficient radius. After about three years of hard daily use his prediction came true while I was driving wide open on the freeway. The break was right at the back end of number three rod journal and clean as a plasma cut. Ball bearing fourth main.
The way I understand the ball bearing ball caps currently available is that they are a press fit onto either the tail shaft or a collar that is locked (bearing retaining compound) onto the main output shaft. I readily agree with you that the bearing needs to be able to slide to & fro and not held captive as both accessory ball bearing set-ups I've seen. Just extracting "food for thought".
The defective bearing i found was not sealed but had a sheild on the rear and the front was open??Maby sealed compleatly would have survived but i did not build it.Bud.
Which had aluminum pistons and which had cast iron pistons?
I used a sealed ball bearing (Sealed Both Sides) having a smaller I.D. compared to the clutch plate out put shaft O.D.
Machined the out put shaft to be a snug fit inside the ball bearing. Care must be taken so the out put shaft can move in and out with firm hand pressure. You do not want the out put shaft to be a loose fit allowing the shaft to spin in side the bearing race.
Using a sealed ball bearing 4th main made a big difference in the amount of oil being lost thru the original Babbitt style bearing.
Also, having a bent transmission shaft could give you a false 4th main bearing fit If you are determining proper transmission/pan alignment based on the ease of how the 4th main slides in place.
I do not recommend using a ball bearing 4th main that requires the bearing I.D. to be bonded to the out put shaft.
J and M,
In your last image, showing the 3 small cracks, what would your thoughts be on die grinding away a bit of material in that area and rechecking? Assuming the short cracks are also shallow, would removing them be an option? (Obviously the ground area would have to be nicely blended and not too deep.)
Good question deserves a good answer.
The cracks even though minute are as deep as they are long. Though you may think it's part of the forging process that they're there. The cracks are square in the middle of the forge mark.
However the cracks also intersect where the crank flexes.
I have placed this picture to show that not all crankshafts have monumental cracks in them as even small cracks as these 1/8" long are enough to render the crankshaft useless.
I make note to our customers and in this chat room such as a piece of glass with a crack so will a crankshaft continue to crack.
It's just good business to not install a part that you know will fail.
The picture below is one from Chicago a customer bought the car off of Ebay. The car had less than 500 miles on a "New" engine.
There is one more factor that has not been mentioned. Were the main bearings recently tightened by removing some of the shims from the main bearing caps, especially the center main?
I have seen crankshafts break within a few hundred miles of having several shims taken out of the center main cap. In hind sight removing the shims threw the crankshaft out of alignment resulting in a broken crank.
It may just be me, but I have seen more two piece Cleveland Hardware forged crankshafts than all other brands combined. I am just superstitious enough that I refuse to use one in a rebuild.
I would like to extend my appreciation to all of you that have helped compile this information and hope we can keep bumping this up to the top of the threads for a while for any additional input.
Original 1909 open valve engine, still with no babbit in the block, probably original crank, unknown mileage with 5 thou oversize pistons fitted. Pulling up gentle incline about 25mph, snapped just in front of #4, probably due to wear on the centre main, smashed rear main out of block, wrecked flywheel & stator.
Rear main metal-stitched back into block, rebuilt with babbit mains, EE crank and sleeved back to std. Still go touring but take it easy.
Have you compiled the data into a spreadsheet or anything and sorted to see if there is a common denominator? Like I say, a cursory glance doesn't seem to reveal one, but careful sorting of the data may.
Steve, I have joined the two piece crank club twice.
1. First time engine was rebuilt the second was the same block, same babbitt, I just ran a line reamer down the mainline and reseated the babbitt.
2. the first was an early Diamond web and the second was a late EE the Early one had chromed journals. Both cranks were magnufluxed.
3. The first time I was pulling a hill on tour, the second time I was cruising at full throttle.
4. I had my pan checked on a KR wilson pan jig.
5. Both times I was running a ball bearing 4th main cap. I aligned my transmission tail shaft with <=.003" run out.
6. The first crank broke between 3 and 4 in the web and broke the block @ the 3rd main. The second broke between 1 and 2 at the journal.
That block was retired as a MT500 engine. It got a different crank bedded into the babbitt and last I heard it was running fine.
I wonder what Ford said about it? I wonder if Ford said anything about it? Bud.
I am surprised that the EE crank broke.
What is the embossng to look for on a Cleveland Hardware crank. I will have to look through my cranks to see if I have one. Does any of them have the EE embossing?
Was the broken crankshaft a frequent failure at the time when the model T was produced and in every day usage ? Or is it due to very high mileage of our days ?
Is the number of broken crankshafts statistically relevant versus the unbroken crankshafts still on the road ?
Quick overview through today:
I've got 29 reporting - of those early shafts total 14 - late style (not EE) is 6, EE is at 2 and 2 were accessory NZ - 5 reported cranks were not indicated as to type.
Of the 29 reported, Babbitt ball caps were 10, ball bearing was 9, other was 1 and 9 didn't indicate.
Just for S--ts & Giggles !
I have rebuilt a couple engines that came in with the new fiber timing gear with stripped gears and broken crank, now did the gears let go first and back fire to break the crank or did the crank break and strip the gears? I guess we will never know the answer to that one.
I've run across the "stripped" fiber gear several times BUT no broken crank - car just died on the spot.
I think the fiber gears are a safety link when a crank breaks with fiber gears the gear strips.
with steal gears more force is on the block and the web breaks.
I contribute my two piece crank to miss alignment of the center main as Trent Boggess stated.
Fiber timing gear didn't save mine Dean.
"I think the fiber gears are a safety link when a crank breaks with fiber gears the gear strips. "
I'm a firm believer that it's the other way around. How does a broken crank strip a gear? The fiber gears quite often strip in an identical manner without crank breakage. The argument here being that you don't need a broken crank to strip a fiber timing gear. But, if you're unlucky, a stripped gear will break your crank, (see Joe Bell's reasoning above). What about cranks that break without the aid of a stripped gear you might say? There's lots of reasons why cranks break. I believe fiber gears are just one of them.
If the crank breaks between 1 and 2 it is possible that no 1 will fire after the break and push the front of the crankshaft on a angle which would break the gear. Most likely the crankshaft broke first, then the gear.
We lost a crank in the speedster a few years back. It was a Suremike and broke between #2 rod & the center bearing. It was not magnafluxed. It was being driven at about 35-40 mph when it broke, however Carolyn had been lugging the car the day before, low band problems, this may have contributed...
When we were on the Alaska tour in 2007(?) someone lost a crank, again near the front as the camshaft gear lost most of the teeth. This was not driven fast or lugged during the three previous days.
Here is my contribution. Broke as clutch was let out going into top from a slow start at about 5mph. The shiny part of the shaft at the crack was about the size of a dime,
That was 30 plus years ago, car now has an EE shaft, ball bearing 4th main which has a slide fitting between the bearing and the output shaft, so I don't go with Jerry's theory. Car has done 50,000 miles since.
Our club engine builder has this fence around his workshop. About 3 out of 5 shaft tested turn out to have cracks. Now its possible to get Scat ones that would appear to be the best option for anyone doing a full rebuild
I attribute my broken crank...at the flywheel flange...through using a four dip pan on an early block/hogshead without the '26-'27 pan *L* brackets and support straps. Dumb.
I'm a two time member, much to the old mans amusement...
Speedster had been rebuilt initially with new babbit, early crank ground at .010" with good radius. Straight, but early sump correct for 1915. Alloy pistons, late rods, no magnets, Reeder head with about 5.5:1 compression. Chaffin cam, alloy intake manifold, straight bore Holley NH, tube steel exhaust headers. Ruxtell with 3:1 & little weight in the car overall.
4th main was ball bearing, slide fit but not machined perfectly concentric.
Owing to an overheating incident the engine was built a second time with arount 6:1 compression, new pistons & much more attention paid to transmission alignment and remachining of the 4th main.
Ran much sweeter the second time around,to the point it would pull 62mph wide open with mudgaurds, windscreen and two on board.
The day following the 'demonstration' race revival weekend I'd done, I was tooling around town, part throttle acceleration & it went bang... clatter clatter clatter.
Turned the crank handle & it seemed to be connected to the flywheel so I restarted it & promptly stopped it again.
Gotta run for now...there is another to detail later