Cracked crankshaft counterweight: Repairable?

[rumcustom]

It’s not from a b-body, but I have a 1957 392 hemi block and crank getting cleaned, manafluxed, and a sonic check at a shop that I use. They called today and said they found a crack in one of the counterweights on the crank. They tried to grind it out to determine how extensive it was and after it didn’t get any smaller they stopped and called me. I don’t have pictures yet, but I’d like to know if something like this can be reliably repaired.

I would think that a repaired crack in this area (If that is even possible) would limit you to a max rpm, and this engine would not see anything over 5000 but still I don’t want to take chances. If anyone here has experience or real knowledge of how to fix something like this please comment. The only option for a new crank is very expensive, and used cranks are hard to find. Thanks

 

[toolmanmike]

Repairable? May be. Should you? I wouldn't. I lost a good friend because he continued running a known cracked crank. It broke, oiled the tires, and he died in the crash. Your choice!

 

[zyzzyx]

The problem with that repair is that you have to grind all of the crack out, check the crank for straightness,
and then preheat it to 300F and then weld up the area. After that, the crank must be stress-relieved at around
1100F. Then you blast it and re-grind all of the surfaces. Not really worth it!

 

[MoparLeo]

392 cranks are the most available of the Generation 1 Hemi's. They were used for racing until the mid 70's. Lot's of used cranks out there.

 

[rumcustom]

392 cranks are the most available of the Generation 1 Hemi's. They were used for racing until the mid 70's. Lot's of used cranks out there.

Really? I’ll keep looking. Maybe the most available of the first gen, but not easy to find for a fair price.

 

[rumcustom]

The problem with that repair is that you have to grind all of the crack out, check the crank for straightness,
and then preheat it to 300F and then weld up the area. After that, the crank must be stress-relieved at around
1100F. Then you blast it and re-grind all of the surfaces. Not really worth it!

Thanks for the details. This is the information I was looking for (what it would take to repair). If the block checks out I’ll step up my search for a used replacement crank.

 

[rumcustom]

Repairable? May be. Should you? I wouldn't. I lost a good friend because he continued running a known cracked crank. It broke, oiled the tires, and he died in the crash. Your choice!

Terrible to hear about your friend. Thank you for sharing.

 

[69Bee]

First, cranks are welded all of the time to repair, balance, or build up journals. This is easy as it is a forged steel crank, so it isn't as difficult as welding a cast crank. Forged cranks are heated cherry red (technical term for hot as fk..) the the hammer forge hammers it into shape. Other processes are performed until it is finally ground to size. It is not uncommon to find forged cranks that look like there is a crack, but in fact, it isn't. Even if it is, have it ground out, weld up the throw. dress weld, and have the rotating assy balanced. My explanations are a little vague, but I have a cold and my brain hurts...

 

[69Bee]

Here is a link to "CNC Motorsports" for a forged 392 crank for a really good price considering what it is. Scat Crankshaft Forged Chrysler 5.7 6.1 3.795 4-HEMI-3795-6125 |CNC-Motorsports

One thing you have to remember when you are looking at price, you are talking about an early hemi, not a 318 Dodge or 350 Chevy or 302 Ford. I built a '54 331 for a customer and he was in it for over $8K. My 331 Hemi is getting special treatment, and the short block is at about $6.5K, and the upper end is going to be about another $12-13K...

 

[dvw]

Here is a link to "CNC Motorsports" for a forged 392 crank for a really good price considering what it is. Scat Crankshaft Forged Chrysler 5.7 6.1 3.795 4-HEMI-3795-6125 |CNC-Motorsports
..

These are for gen 3
Doug

 

[MoparLeo]

331 parts are not as plentiful as 392/354.

 

[F4R/T]

Check with that company Hot Heads, they are well known for early Hemis.

 

[69Bee]

These are for gen 3
Doug

You are correct. After I shut the computer off, I wondered if I had missed that, and I did. Still getting over the cold...

 

[69Bee]

Check with that company Hot Heads, they are well known for early Hemis.

Another thing I was going to mention, but didn't want to fire the computer back up...

Hot Heads Research & Racing Early Chrysler Hemi Engine Parts (hothemiheads.com)

 

[rumcustom]

First, cranks are welded all of the time to repair, balance, or build up journals. This is easy as it is a forged steel crank, so it isn't as difficult as welding a cast crank. Forged cranks are heated cherry red (technical term for hot as fk..) the the hammer forge hammers it into shape. Other processes are performed until it is finally ground to size. It is not uncommon to find forged cranks that look like there is a crack, but in fact, it isn't. Even if it is, have it ground out, weld up the throw. dress weld, and have the rotating assy balanced. My explanations are a little vague, but I have a cold and my brain hurts...

So you’re saying that welding a crank counterweight is acceptable. I didn’t tell my shop to do it, I just told them to stop for now when they asked me what I wanted to do next with the crank. I realize since this is a forged crank it’s easier to weld than cast but I didn’t know one way or the other if welding A counterweight was OK. As I said they were grinding the crack to determine how bad it was and stopped grinding when it didn’t go away. I guess the real answer is that I need to get the machine shop and see it for myself. When I do I’ll take pictures and post them up here. Thanks for your input

 

[Gsmopar]

There is some Gen I hemi stuff on Racing Junk.

https://www.racingjunk.com/search?quickSearch=1&categoryId1=6&searchString=hemi

 

[RJRENTON]

The problem with that repair is that you have to grind all of the crack out, check the crank for straightness,
and then preheat it to 300F and then weld up the area. After that, the crank must be stress-relieved at around
1100F. Then you blast it and re-grind all of the surfaces. Not really worth it!

True.....repairing a forged crankshaft is problematic at best....and involving a complex and expensive procedure. IMO, the grind, pre-heat, weld (TIG is best for the root pass, followed by MIG cover passes) maintaining at least 300°F interpass temperature, followed by a post weld heat treatment procedure to normalize (annealing) the weld joint stresses, followed by checking for straight-ness, overall and by adjacent journals followed by re-balancing. The unknown factor may be the filler metal to use. To be totally compatible, you would need to know the alloy of the crankshaft. Is it: SAE/ASTM 1045, 4140, 4130, 8620 or some other chrome molly nickel alloy and the percentage of carbon....all "carbon steel is NOT the same". If it is a high carbon alloy crankshaft, using a low carbon alloy filler metal will reduce the overall joint strength by dilution of the weld bead interface to parent metal which usually results in under bead cracking. SHORT ANSWER: DON'T WASTE THE TIME OR MONEY TO ATTEMPT A REPAIR. Not knowing what you are welding or using the in-CORRECT/or compatible filler metal can result in disastrous and expensive results..... just my opinion of course....
BOB RENTON

 

[rumcustom]

Thanks Bob, and everyone else. These particular cranks are hard to find and when you do see one they’re expensive compared to a lot of other OEM pieces out there. You know how it goes, when you already have one and you think it’s good and then you find out it’s bad you start wavering for a while. At least I did.... couldn’t just let it go. The risks are not worth the reward and this crank will become artwork at my shop, at best. This is why we check them so that we can know if they’re good-to-go or junk and mine turned out to be junk. It happens. Now I just have something else to add to the list for what I search for every day. Lol

 

[Dipstick]

I don’t have pictures yet, but I’d like to know if something like this can be reliably repaired.

Pics would be nice.

 

[rumcustom]

Pics would be nice.

Couldn't make it to the machine shop today. Will post a pic when I get it.