An LS1 crankshaft can look perfectly healthy and still belong in the scrap pile.
That’s because not every crankshaft defect is obvious to the naked eye.
A journal may look smooth. The crankshaft may measure correctly. It might even pass a runout check.
None of those inspections necessarily tell you whether the crankshaft contains a crack.
For that, the LS engine-building reference recommends magnetic-particle inspection. The crankshaft is placed on a specialized inspection station, magnetized and examined under ultraviolet light so cracks can become visible.
And the source is refreshingly uncomplicated about what to do when one is found:
Replace the crankshaft.
Here’s what the inspection does and why it’s worth considering before an LS1 short block goes back together.
Why Should You Check an LS1 Crankshaft for Cracks?
Crankshaft inspection involves more than measuring journal diameter.
The LS reference specifically states that the crankshaft should be checked for cracks and flaws. It identifies magnetic-particle inspection as the preferred method for finding them.
That’s important because dimensional measurements answer dimensional questions.
A micrometer can tell you a journal diameter.
A dial indicator can tell you whether the crankshaft has excessive runout.
Neither measurement, by itself, establishes that the crankshaft is free from cracks.
That’s why crack inspection deserves to be treated as a separate step.
What Is Magnetic-Particle Crankshaft Inspection?
Magnetic-particle inspection is a nondestructive testing method used to reveal discontinuities in suitable ferromagnetic components.
For the LS crankshaft procedure described in the supplied reference, the crankshaft is mounted horizontally on a magnetic-particle inspection bench.
It then passes through a large-diameter circular magnet and is examined using ultraviolet—or black—light. The reference says cracks become visible as light-colored lines during the inspection.
The purpose is straightforward:
Find defects that may not be apparent during an ordinary visual inspection.
Is This the Same as Magnafluxing an LS1 Crankshaft?
You’ll frequently hear engine builders call the procedure Magnafluxing.
The supplied LS reference points out an important terminology detail: Magnaflux is a brand name, even though the term is commonly used conversationally for magnetic-particle inspection equipment.
The book specifically notes that other manufacturers, including DCM, produce this type of inspection equipment.
So technically, the process we’re discussing is:
Magnetic-particle inspection
Calling every machine a Magnaflux machine is a little like calling every adjustable wrench a Crescent wrench.
Everyone knows what you mean. The trademark attorneys may be less enthusiastic.
How Is an LS Crankshaft Checked for Cracks?
According to the LS engine-building reference, the crankshaft is mounted horizontally on the inspection station.
A large circular magnet passes over or surrounds the crankshaft while the technician examines the component under ultraviolet light.
The inspection is performed specifically to identify cracks or flaws in the crankshaft.
This isn’t the same setup used for checking runout.
Runout requires supporting and rotating the crankshaft while monitoring it with a dial indicator.
Crack inspection requires specialized magnetic-particle testing equipment.
Two inspections. Two different questions.
What Does a Crankshaft Crack Look Like During the Test?
The LS reference describes cracks becoming visible as whitish lines when inspected under ultraviolet light.
That’s the critical advantage of the inspection described by the source.
Instead of relying entirely on what can be seen on an untreated crankshaft surface under ordinary shop lighting, the inspection makes defects easier for the technician to identify.
Interpreting the indications should be left to someone experienced with the inspection equipment and crankshaft evaluation.
Finding a line is one thing.
Knowing exactly what the indication represents is another.
Can You Find LS1 Crankshaft Cracks With Your Eyes?
A visual inspection is still worthwhile, but the source specifically recommends magnetic-particle inspection for crankshaft flaws and cracks.
That tells us something important about the limits of simply looking at a used crankshaft.
If a crack is large enough to be glaringly obvious, you probably don’t need sophisticated equipment to decide the crankshaft shouldn’t go back into the engine.
The inspection becomes particularly useful for finding defects that aren’t immediately apparent.
“Looks fine from here” remains a surprisingly poor engine-building specification.
Is Crankshaft Crack Inspection the Same as Checking Runout?
No.
This is the most important SEO and technical distinction between this FAQ and our crankshaft-runout guide.
Crack inspection looks for structural flaws.
Runout inspection determines whether the crankshaft is bent.
The supplied reference treats them as two separate procedures. For runout, it places the crankshaft on level V-blocks or a polishing station and monitors the No. 3 center main journal with a dial indicator as the crank rotates.
A crankshaft can therefore require multiple inspections before being approved for reuse.
Passing one doesn’t magically perform the others.
Can a Straight LS1 Crankshaft Still Be Cracked?
The inspections answer different questions, so a satisfactory runout measurement should not be interpreted as a crack inspection.
The reference independently recommends checking the crankshaft for flaws/cracks and checking it for runout/bend.
That’s why this FAQ shouldn’t collapse those inspections into one pass/fail judgment.
A dial indicator measures movement.
Magnetic-particle equipment reveals indications of defects.
Don’t ask one tool to do the other’s job.
What Should You Do If an LS1 Crankshaft Is Cracked?
Replace it.
This is one area where the supplied LS reference leaves very little room for interpretation.
After describing magnetic-particle inspection, it states that if the crankshaft is cracked, it should be replaced.
That means this article isn’t going to offer a section titled:
“Five Clever Ways to Save Your Cracked LS1 Crank”
There isn’t one.
A detected crack isn’t a journal-polishing problem or an invitation to experiment with repairs.
According to the reference we’re using, the crankshaft gets replaced.
Is a Cracked Crankshaft the Same as a Scratched Journal?
No.
Surface condition and structural cracking aren’t interchangeable terms.
The LS reference separately discusses crankshaft journal inspection and machining. If a journal requires regrinding, the crankshaft is machined on dedicated crankshaft-grinding equipment.
That is fundamentally different from the source’s treatment of a cracked crankshaft.
A dimensional or surface problem may lead to machining depending on its condition.
A crack leads to replacement.
That’s an important distinction when deciding whether a used crankshaft is worth additional machine work.
Should a Used LS1 Crankshaft Be Crack-Tested Before Machining?
The reference recommends inspecting the crankshaft for flaws and cracks as part of the crankshaft evaluation process.
Practically, establishing whether a crankshaft is structurally usable before investing heavily in additional machining makes sense.
The source doesn’t provide a rigid universal order for every machine-shop operation, however, so we shouldn’t invent one and present it as an LS factory procedure.
The source-supported takeaway is simpler:
Crack inspection belongs in the evaluation of an LS crankshaft before it is approved for reuse.
Does a New LS1 Crankshaft Need the Same Inspection?
The supplied reference discusses crankshaft inspection as part of evaluating the crankshaft for an engine build, but it doesn’t establish a universal rule saying every newly manufactured crankshaft must undergo magnetic-particle inspection.
So there isn’t a source-supported reason to turn that into an absolute requirement here.
For a used crankshaft—or one with unknown history—the value of checking for flaws is considerably easier to understand.
For new aftermarket components, follow the crankshaft manufacturer’s documentation and your machine shop’s inspection practices.
Can You Perform Magnetic-Particle Inspection at Home?
The procedure described in the LS reference uses a dedicated magnetic-particle inspection station, a large circular magnet and ultraviolet inspection.
That’s machine-shop inspection equipment, not the usual collection of sockets, breaker bars and questionable extension cords found in a home garage.
For the inspection described by the source, this is a job for a properly equipped engine or crankshaft machine shop.
That’s not necessarily bad news.
The crankshaft is already out of the engine.
Now is exactly when you’d rather discover the problem.
What Else Should Be Checked on an LS1 Crankshaft?
Crack inspection is only one part of evaluating a crankshaft.
The LS reference also provides specifications and procedures for checking dimensions and runout. Among its OEM LS crankshaft specifications are:
| Measurement | Reference Specification |
|---|---|
| Runout | 0.00118 in. max/production |
| Main journal diameter | 2.558–2.559 in. |
| Main journal taper | 0.0004 in. max |
| Rod journal diameter | 2.0991–2.0999 in. |
| Rod journal taper | 0.0002 in. max |
| Crankshaft end play | 0.0015–0.0078 in. |
Those measurements are useful supporting context, but they shouldn’t become additional SEO targets for this article.
Your existing Pro Street crankshaft-end-play page already owns that measurement, for example.
This page has one job:
Finding cracks in an LS1 crankshaft.
Don’t Spend Money Machining a Crankshaft Before You Know What You Have
Building an LS1 involves plenty of measurements measured in thousandths of an inch.
Crack inspection is different.
You’re not trying to determine whether a dimension is two ten-thousandths outside your preferred clearance.
You’re trying to establish whether a structural defect exists.
The LS engine-building reference recommends magnetic-particle inspection for this job. The crankshaft is mounted horizontally on the inspection station, magnetized and examined under ultraviolet light so crack indications can be identified.
And if the crankshaft is cracked?
Replace it.
Sometimes engine building really does provide a wonderfully simple specification.
LS1 Crankshaft Crack Inspection FAQ
How do you check an LS1 crankshaft for cracks?
The supplied LS engine-building reference recommends magnetic-particle inspection using specialized inspection equipment and ultraviolet light.
Is magnetic-particle inspection the same as Magnafluxing?
Magnaflux is a brand name commonly associated with magnetic-particle inspection. The reference specifically notes that other manufacturers also produce this inspection equipment.
What does a crankshaft crack look like during magnetic-particle inspection?
The supplied reference describes cracks appearing as whitish lines during ultraviolet-light inspection.
Can crankshaft runout testing find a crack?
Runout and crack inspection are different procedures in the supplied reference. Runout checks for crankshaft bend with a dial indicator; magnetic-particle inspection checks for cracks and flaws.
What should you do with a cracked LS1 crankshaft?
The reference says to replace it rather than debate whether it should be reused.
Does a good runout measurement mean the crankshaft is crack-free?
No. The reference treats runout inspection and crack/flaw inspection as separate checks.