MTFCA Forum

I pulled the engine out of my 1925 Coupe. It had a few things wrong with it so I decided to take it out. First thing I did is have the crankshaft magnafluxed as always. In the attached photo, you will see a photograph of a 1/4 inch long crack in the #4 rod journal. I am considering putting it back in the car. Here are my reasons why. Please keep your rebuttals polite and thought-provoking. Making a blanket statement of "ITS CRACKED, REPLACE IT..." does nothing for good dialogue.

Here's why:
1, From the looks of the crack, and the fact that I can feel it with my fingernail tells me it's been there for years. The edge of the crack is rounded, speaking to years of use, polishing the sharp edge away to a rounded bevel.
2, The crack runs axially... along the length of the journal. If it ran diametrically, I would replace it without another thought. But this crack is not cutting the journal in two.
3, It's in the downward stroke side.... meaning it's in the crux of the crank, so when the piston fires, and pushes down hard on the journal, the crack is being forced closed... not open. I doubt this scenario promotes rapid crack growth.

In the end, I may choose to replace it. But a crack this small, running in this direction doesn't make my alarm bells go off. Forget that we live in a world of Scat cranks. If you only had this one to use, lets figure out what everyone thinks the probability of failure is?
And GO....

Could just be a deep gouge. I would have it magnafluxed to check. On my own car if it passes that test I would use it, customers car no.

You didn't say "Wet magnaflux" as if it was done dry it only gives a one dimensional image whereas the Wet mag will give all three.

I think you are taking a big chance. If the car is rarely driven, then maybe you can get by for a while, however, it could break at any unexpected time and cause great damage to the engine or other parts. When it breaks, the car will suddenly stop and other parts could also break.
If you are planning to sell the car, it would also be unfair to the potential buyer if you were not to disclose this information. Also remember that this location has the most pressure of any place on the crankshaft because of the pressure of the first three cylinders firing, this location will not only take the pressure of number 4 but will be twisted by the other 3.
It is really a very lucky thing that you found this crack before anything broke because you might even be able to save the babbit. If your bearings are undersize, but the babbit is sound, you could bore them out to standard and fit a brand new crank in the engine. The new SKAT crank will cost a bit, but you can get one in standard stroke and the only difference is counterbalance. It really runs smooth and is stronger than the original crank.
So, the expenditure for a new crank now, could actually save you from having to replace the entire engine or even more in the future.
The decision is yours to make, but if it were mine, I would replace the crank.
Norm

Sounds a bit like you're trying to talk us and yourself into reusing it. At least do that follow up wet magnaflux test & make your decision based on that.

Charlie... you are not entirely wrong. I'm not trying to talk anyone else into anything. I'm just presenting what the shop found today, and my take on the crack. In response, I'm fishing for feedback. I never use this car. It hasn't had 100 miles put on it in the last 40 years.. But it's been in my family for 72 years and its here to stay. I at least want to be able to start it up and move it around.... maybe take it on a 10 mile run once a year. But it will NEVER be a tour car. And because of that, I cannot justify 1500 bucks for a Scat crank. So, I either need to find a good used crank that measures 1.245 all the way around, or calculate my probability of destruction...

Why not have it x-rayed. I believe that is how they confirmed the quality of the weld on my 1908 Locomobile crank.

I don't have enough experience to say one way or another . I know I don't take the engine out of my car unless I have to! Lol...

My question is one of curiosity..... (Of course, now that I've started a reply, I don't remember if the crack was on a babbitt/bearing location, or attached to a rod.) In any case... What does it's mating surfaces look like? Is there a noticeable wear pattern where the crack is?

James I believe the decision is yours and yours only. If you accept it and it does fail then you knew the risk. Either way having fun is what is all about.

On a side note.., knew a guy with the same issue some 40 years ago. As far as I know it is still running fine.

Hank

This has been debated a few times several years ago but I can't find it with a search, we all know that with a radial crack it's scrap, a time bomb waiting to go off but with a horizontal crack, no one has ever seen a crank split the length of a journal unless someone can say so now. The consensus back then was that many a shaft had horizontal cracks from maybe new and if not effecting the Babbitt any it wasn't to be an issue. But if it grows any more in length, what effect it will have on the bearing would be the big question. Choice is still going to be yours..

I'm not sure where you are in W Virginia, but I'm going to be set up in Carlisle next week in spot D33-35 and I can bring two used crank shafts for you to look at. They both have been magnafluxed and polished on a crank machine (not ground, polished). The both have standard mains and .010 under rod journals. Either one, $200.

Frank
518-755-0986

Even if it's not a radial crack, it's evidence of crystalized metal structure in the crank. Even if it doesn't go now, nothing is saying that you won't develop a radial crack in that crystallized metal structure. How much is your time, patience, and engine worth? If not much, then run it, and when it breaks, know you have a pretty big hassle and expense ahead of you.

This is (to me) a craps table gamble... you can keep rolling the point over and over, but eventually you'll roll a 7. How's your luck? And speaking of, you need to factor in 2020. Normally, no, but after this year... while it's apart I'd drop a new Scat into it and not worry, rather than wonder "will THIS be the trip that breaks my baby?" every time you venture forth.

That's just my opinion. Just the crack being there means there's damage in the metal of the crank.... and that means while the linear crack may not fail, nothing will stop that crystalline structure from biting you elsewhere.

James, in your original post you said, "First thing I did is have the crankshaft magnafluxed as always."

Have you actually magnafluxed this particular crank in the past ? Was this same flaw seen previously ? If yes, then the only question you need to consider is whether it has grown since the last time you looked at it. If you have looked at the crank before and this is the first time you have seen the flaw, then I'd be worried.

The other possibility is that this is the first time you have ever inspected the crank and you have no idea if the flaw is a long time feature. Then we're not much smarter other than your observation of the wear evidence along the edges of the flaw.

Making the decision to replace or not is another subject. Is this the original block with correct serial number ? If so, it may have some intrinsic value and you would be more interested in protecting the block. If it's not the original block, then your only decision is whether to definitely spend a good wad of cash now or (maybe) to spend a somewhat larger wad sometime in the future.

Your decision is a lot like buying insurance. What is the chance the event will occur ? What is the cost of the potential occurrence ? How much money are you willing to spend to offset the cost of some potential greater cost in the future ?

Dick

I have seen forging lines run across two throws of a crank, they look like cracks on a wet mag machine but they are rolled pieces of steel in the forging, this could be one of those? not saying it is but possible?

Many years ago while on a tour I had number 1 rod get loose in a freshly rebuilt engine. When I dissembled the engine I found a longitudinal crack on number 1 crank journal. It was about 3/4 inch long and could barely be felt by dragging a fingernail across it.

So I'm of the opinion to get a good used crank.

Also check for main bearing wear. The center bearing wears faster than the others, and the looseness is often taken up by removing shims. That puts the crank out of alignment and leads to crank breakage, usually at one of the rod journals.
Art

I say it's a forging flaw and not a crack. "Crack" suggests something that was not always there, but has developed over time, use, stress, etc. I would propose that what you're seeing has been there since day one.

Find a used/new crank and replace it. The car has been in your family for many years and you will be passing on to a family member. This has been an interesting post with lots of info, but its time to fix your car for the next owner.

I agree. What's to gain by taking a chance on it?

I remember speaking to Bruce McCalley on this very subject, well actually was it worth magnafluxing a model T crank. He advised not bothering as most T cranks show some crack somewhere. So on my coupe, which was rebuilt in 1990, was just reground and rebabbitted. So far it’s been fine.
Of course both the speedster and the 14 touring broke cranks while in use and previous writers are correct, it’s expensive.

Has anyone real first hand experience of finding an original Ford crank that has shown no cracks after magnafluxing.

By the way just reboring often doesn’t work as the end play on #3 main bearing us not correct. I tried doing that on the speedster and the end play and crank placement was way off what it should be in a good motor.

Quote "Has anyone real first hand experience of finding an original Ford crank that has shown no cracks after magnafluxing. "

Yes we have.

We had a customer a while back go to Langs to see what they had for cranks and Lang's Allowed him to choose the ones he wanted as he only needed one but brought three for us to test. Once they were cleaned all passed the test. It does happen. Not everyone can afford a Scat crank. Though most often the engine we get to rebuild the cranks are usually cracked due to hard driving and being nearly 100 years old.

We had a crack similar to that on an equipment crankshaft. We ground the crack some just to get rid of the sharp edge running against the bearing , and ran it. It never did brake, but the bearing did go out again. This was done in frame.

TonyB wrote: ↑

Fri Sep 25, 2020 1:45 am

Has anyone real first hand experience of finding an original Ford crank that has shown no cracks after magnafluxing.

Read my post above...

My biggest concern would be that as Norman Kling said, you would have an obligation to tell any person that you might someday sell the car to that it has a cracked crankshaft. If I were that potential purchaser, in my mind I would be thinking that before I ever drive the car, the engine has to come out and have the crank replaced. If I'm going that far, the engine would have to be disassembled and at least the rings and babbitt inspected carefully. To say that this would have an impact on what I would be willing to pay for the car would be like Noah saying "it looks like a little rain."