Broken crankshaft. Worth saving the rest?

denverslim

denverslim

Senior Member
Trying to help out a friend without computer or tech knowledge.
Model B engine. Not many miles on rebuild. Valves, pistons, rings are all looking good. Crank is broken just inside the rear flange. So now, since we need a new crank should we just get a whole engine with crank, or try to find someone to fit a new crank into this one. I assume we would need to babbit all bottom end of rods and main to match new crank. Not easy to find.
Can get a used "A" engine for 500 to 1k. Although I don't know how many miles are on it.
Am not having any luck finding anyone locally who does babbit work.

Any ideas?
 
I would love to see pix of that crank shaft, what caused it to break? Bert's is your go to operation, if they can't do it, they know where to send you.
 
A broken Model T "hairpin" crankshaft is a common occurrence and no big deal. We're seeing lots more of that these days in the Model T community as the metal in these cars continues to age and become more brittle. But a broken Model B crankshaft with its comparatively huge journals IS a rarity. Or for that matter, even a broken Model A crankshaft. Not being a professional engine builder - yet a fairly serious restorer since 1966 - I can't recall the last time I saw a broken Model A or even Model B crankshaft that hadn't been messed with, such as for stroking purposes. Probably not that many guys in the Model A community have laid a Model T crankshaft next to a Model A or B shaft. The difference in size is startling! One wonders how a Model T crankshaft that supports a really heavy flywheel/magneto/transmission assembly (much heavier than a Model A flywheel/pressure plate) could have lasted as long as it has for 100+ years. I wonder what would have caused a Model B crankshaft to break unless there was some serious misalignment or line boring issue going on there.
Yes, I'd love to see a photo of the break in the Model B crankshaft, too. It'll go in my file of photos showing Bigfoot, aliens from outer space and the Loch Ness Monster because they are all equally rare.
Marshall
 
The counterweighted Model-B crankshafts were rather thin at the cheeks on both ends of the throws when compared to the non-counterweighted A and B crankshafts. It is not uncommon for them to break at the point where the #4 crank web meets the rear main bearing, especially when the crank has been drilled for pressure or if no radius filets were ground at the journal ends.
 
Yes, I've heard of them cracking, especially the third iteration of Model B crankshaft with the counterweights cast as part of the crank. But actually breaking? I'm sure professional engine builders have seen their share of broken cranks, but for the rest of us, that would be an extreme case. By the time the pro's are given the engine, it's usually in need of many major repairs, such as block cracks, burned valve seats and cracked/broken cranks. Maybe I've just been lucky so far?
Marshall
 
Bert doesn't like to do "partial" rebuilds and we are trying to respect that. We would rather not tear into the upper end at this time though, as miles since rebuild are low and all looks good up there. I just hate to tear the entire engine down for a rebuild unless it is absolutely necessary.
We're hearing the gasps and wow's here locally as no one yet has any familiarity with broken cranks on these. As soon as I can figure out how to do it I'll post some pictures...
 

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We're still shaking our heads too.
Maybe it was dropped before installed. ???
Ok, back to the original question, where would you go now?
Thanks for any ideas, we really don't want to start all over, but...........?
 
Have you called Herm Kohnke ? He has 50 + years working with Babbitt.

He works with MANY kinds of engines ... some are "one of a kind" not just Model A.

He might be able to help.

Kohnke Machine & Repair
60615 330th Avenue
Clare, IA 50524
Phone: (515) 546-4551

Here is an "About me" page on FB about Herm:

You could send him a private message to get a hold of him.

There is a link on this page to send PM to him.

https://www.fordbarn.com/forum/member.php?u=439
 
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A good welder might be able to fix that, then have the flange trued up on a lathe. Best place would be a crankshaft specialist. They are forged steel which should be weldable.
 
I'm with Tom. The crank is broken on the flange, not inside the engine. I would think the main bearing is still ok. It would be easy enough to have another crank ground to match your old crank in diameter on the rods and mains and be able to replace with out going threw the rest of the engine if it is still in good shape.
 
I'm also in for the weld and truing on a lathe which would be an easy fix for a qualified machinist, you don't have much to lose. If it doesn't work many other options are open, I would keep the present engine. Welded and machined properly that spot on the crank will be the strongest part of the engine. also we are not talking big HP and torque here..
 
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denverslim said:
Trying to help out a friend without computer or tech knowledge.
Model B engine. Not many miles on rebuild. Valves, pistons, rings are all looking good. Crank is broken just inside the rear flange. So now, since we need a new crank should we just get a whole engine with crank, or try to find someone to fit a new crank into this one. I assume we would need to babbit all bottom end of rods and main to match new crank. Not easy to find.
Can get a used "A" engine for 500 to 1k. Although I don't know how many miles are on it.
Am not having any luck finding anyone locally who does babbit work.

Any ideas?
Click to expand...

Do not scrap the block. Some one can find a crank. B cranks have broke there before. I'm not a fan of welding the flange back on. It might work if the welder knows his metal and the stress that will be involved. But I would find a better crank. How about a new one.
 
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denverslim said:
Bert doesn't like to do "partial" rebuilds and we are trying to respect that. We would rather not tear into the upper end at this time though, as miles since rebuild are low and all looks good up there. I just hate to tear the entire engine down for a rebuild unless it is absolutely necessary.
We're hearing the gasps and wow's here locally as no one yet has any familiarity with broken cranks on these. As soon as I can figure out how to do it I'll post some pictures...
Click to expand...

Hey slim,
Can you tell the condition of this B crank, i.e.- 'standard', .010 or ?
Picture of whole crank ? Is with or without weld on weights ?
Can't say that I've seen a B crank that was broken like that pic shows !

Reason for asking for whole crank pic and description, is that there are B cranks available. Easier to see what you need if answers, eh .

Interesting pic indeed, thanks for sharing. I guess poor welds do happen !
 
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Actually if you have it welded and it breaks again you potentially have a lot to loose.
The flywheel is spinning and could be like a grenade taking out everything including your legs!
 
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