A crankshaft can look perfectly normal on a workbench and still have a problem that’s measured in thousandths of an inch.
That’s why visual inspection alone isn’t enough when evaluating an LS1 crankshaft.
One of the measurements worth checking before assembling the short block is crankshaft runout.
Runout tells you whether the crankshaft remains centered as it rotates or whether the center of the crank moves because the crankshaft is bent.
The LS engine-building reference describes checking the crankshaft on a level rotating fixture with a dial indicator positioned at the No. 3 center main journal. It gives a maximum production specification of 0.00118 inch and states that a crank measuring less than 0.001 inch is generally considered acceptable.
Here’s how the measurement works and what it tells you about an LS1 crankshaft.
What Is LS1 Crankshaft Runout?
Crankshaft runout measures how much a crankshaft deviates from its rotational centerline as it turns.
Imagine supporting the crankshaft at its front and rear main journals and slowly rotating it.
If the crankshaft is perfectly straight, the center main journal should remain essentially centered during rotation.
If the crankshaft is bent, that journal moves toward and away from a stationary dial indicator as the crank rotates.
The dial indicator records that variation.
That’s crankshaft runout.
The supplied LS reference specifically describes runout inspection as checking the crankshaft for a bend.
What Is the LS1 Crankshaft Runout Specification?
The LS engine-building reference provides two closely related numbers that deserve some explanation.
Its OEM specification table lists:
Maximum production runout: 0.00118 inch
The crankshaft inspection procedure then states that:
Less than 0.001 inch is generally considered acceptable.
The reference says a crank showing more than approximately 0.001 inch needs to be straightened or replaced.
Those figures shouldn’t be rewritten into a fake precision specification.
For practical inspection, the book’s guidance is straightforward:
Less than 0.001 inch of runout is generally acceptable.
The listed production maximum is 0.00118 inch.
Where Is LS1 Crankshaft Runout Measured?
At the No. 3 main journal.
That’s the center main journal of the LS crankshaft.
The reference instructs the builder to support the crankshaft using the front and rear main journals, then place the dial indicator at the center No. 3 main journal.
That center location makes the measurement useful for detecting deviation between the supported ends of the crankshaft.
The indicator probe should also be positioned slightly away from the journal’s oil hole.
Otherwise the indicator can encounter the oil-hole opening as the crank rotates and produce a reading that has nothing to do with crankshaft straightness.
That’s a remarkably efficient way to turn a precision measurement into nonsense.
What Tools Do You Need to Measure LS1 Crankshaft Runout?
The procedure described in the LS reference requires relatively straightforward measuring equipment:
- Level crankshaft rotating fixture or suitable V-block arrangement
- Precision dial indicator
- Rigid dial-indicator stand
- Clean crankshaft journals
- Stable work surface
The reference describes either placing the crankshaft on level V-blocks or using a crankshaft polishing station.
The critical point is that the crankshaft must be supported accurately and be able to rotate without the measuring fixture introducing movement of its own.
You’re trying to measure thousandths of an inch.
A workbench that rocks every time you touch it is therefore less than ideal.
How Do You Measure LS1 Crankshaft Runout?
The LS reference provides a specific procedure.
Support the crankshaft horizontally using the front and rear main journals.
Position the dial indicator against the No. 3 center main journal, with the probe slightly offset so it won’t contact the oil hole.
Then preload the dial indicator approximately:
0.050 inch
Zero the gauge.
Slowly rotate the crankshaft through a complete revolution while watching the indicator.
The amount of variation displayed by the gauge represents crankshaft runout.
Compare the result with the reference’s guidance.
A reading below approximately 0.001 inch is generally considered acceptable according to the source.
Why Do You Preload the Dial Indicator?
The LS reference specifies approximately 0.050 inch of indicator preload before zeroing the gauge.
Preloading keeps the indicator tip in consistent contact with the journal as the crankshaft rotates.
Without sufficient contact, the indicator could lose contact with the journal and give an unreliable reading.
Once the indicator is properly positioned and preloaded, zero the gauge before rotating the crankshaft.
The number you’re interested in isn’t the preload.
It’s the variation observed during rotation.
Why Should the Indicator Avoid the Crankshaft Oil Hole?
Because the dial indicator needs to follow the machined journal surface.
The LS reference specifically says to position the probe slightly offset to avoid hitting the oil hole.
If the indicator tip drops into or crosses an oil opening, the resulting needle movement doesn’t represent crankshaft runout.
It represents the fact that there’s a hole in the crankshaft.
Which, fortunately, GM put there intentionally.
Is Crankshaft Runout the Same as Crankshaft End Play?
No.
These are completely different measurements.
Crankshaft runout checks crankshaft straightness while the crank rotates.
Crankshaft end play checks how far the crankshaft can move forward and backward along its axis.
Your existing Pro Street LS1 Crankshaft End Play guide owns that axial-clearance topic and gives the OEM LS end-play range as 0.0015–0.0078 inch.
This article should not try to rank for that phrase.
The distinction is simple:
Runout = straightness during rotation
End play = axial movement
Same general area of the engine. Entirely different measurement.
Is Crankshaft Runout the Same as Main-Journal Out-of-Round?
No.
This distinction is even easier to confuse.
Runout evaluates whether the crankshaft’s rotational centerline deviates as the entire crankshaft turns.
Journal out-of-round evaluates whether an individual journal remains truly round when measured at different radial positions.
The supplied LS reference lists maximum main-journal out-of-round at:
0.000118 inch
It separately lists main-journal taper at:
0.0004 inch maximum
Those aren’t crankshaft-runout specifications.
They’re measurements of the journal itself.
Keeping those inspections separate is important when evaluating a used crankshaft.
What Is LS1 Main-Journal Diameter?
The LS reference lists the main-journal diameter at:
2.558–2.559 inches
Again, that’s not a runout measurement.
Journal diameter is checked with a micrometer.
Crankshaft runout is checked by rotating the supported crankshaft while monitoring the center journal with a dial indicator.
A crankshaft can potentially have journals that measure correctly in diameter while still requiring a separate straightness inspection.
That’s why engine builders don’t rely on one measurement to describe an entire crankshaft.
What Causes an LS1 Crankshaft to Have Runout?
The supplied reference explains how to inspect the crankshaft for runout but does not provide a comprehensive list of every possible cause of a bent LS crankshaft.
So we shouldn’t manufacture one just to make the article longer.
What the source establishes is that crankshaft runout should be inspected regardless of which crankshaft is being used and that excessive runout indicates the crank requires corrective attention.
The important takeaway for an engine builder is therefore measurement, not speculation.
If you’re dealing with an unknown used crankshaft, measure it.
If you’re dealing with a crankshaft that has undergone machine work, measure it.
If you’re assembling a performance engine with an expensive crankshaft that arrived in a beautiful box containing several aggressive-looking stickers…
Measure it.
Stickers remain notoriously poor measuring instruments.
Can a Bent LS1 Crankshaft Be Straightened?
Potentially, but the reference is very clear that crankshaft straightening is precision work for a skilled specialist.
It also notes that not every crankshaft can be successfully straightened.
That’s an important limitation.
Finding excessive runout doesn’t mean the next step is putting the crankshaft in a press and seeing what happens.
A qualified crankshaft or automotive machine shop should evaluate whether the crank is a suitable candidate for correction.
If not, replacement is the appropriate path described by the reference.
Should You Check a New LS1 Crankshaft for Runout?
The supplied reference recommends measuring the crankshaft regardless of which crank you choose so its condition can be verified before assembly.
That’s good engine-building practice because the assembled engine doesn’t care whether a component is new, used or came in particularly impressive packaging.
It only cares about geometry.
Checking runout before installing bearings and assembling the short block also makes the inspection considerably easier.
The crankshaft is already out.
The journals are accessible.
The dial indicator can be positioned properly.
There is very little reason not to check it.
Should You Inspect an LS1 Crankshaft for Cracks Too?
Yes, but that’s a separate inspection.
The LS reference recommends checking the crankshaft for flaws or cracks and discusses magnetic-particle inspection as the preferred method. It describes the crankshaft being mounted horizontally on an inspection station and examined under ultraviolet light.
A crankshaft that passes a runout check isn’t automatically free of cracks.
Likewise, a crack inspection doesn’t tell you whether the crankshaft is straight.
They’re separate tests answering separate questions.
That distinction also gives us a future LS1 FAQ opportunity without stuffing every crankshaft-inspection keyword into this page.
What Else Should Be Measured on an LS1 Crankshaft?
After checking runout, the reference recommends measuring the main and rod journals.
Its inspection specifications include:
| Measurement | LS reference specification |
|---|---|
| Main journal diameter | 2.558–2.559 in. |
| Main journal taper | 0.0004 in. max |
| Main journal out-of-round | 0.000118 in. max |
| Rod journal diameter | 2.0991–2.0999 in. |
| Rod journal taper | 0.0002 in. max |
| Rod journal width | 1.902 in. |
Those measurements belong to the broader crankshaft-inspection process.
For SEO purposes, however, they should remain supporting information here.
This page has one job:
Explain LS1 crankshaft runout.
What If the Crankshaft Journal Is Scratched?
The LS reference distinguishes surface damage from crankshaft runout.
Light journal scratches may sometimes be addressed by polishing, while damage that can’t be removed through polishing may require crankshaft grinding.
Again, that doesn’t make journal-surface repair the same thing as straightening a crankshaft.
A crank can have a surface problem.
It can have a dimensional problem.
It can have a straightness problem.
Or, because engines occasionally enjoy making life interesting, it can have all three.
Each condition needs to be measured independently.
Check LS1 Crankshaft Runout Before Building the Short Block
Crankshaft runout is exactly the kind of measurement that’s easiest to perform when the engine is already apart.
The procedure from the LS engine-building reference is straightforward:
Support the crankshaft at the front and rear main journals.
Position a dial indicator at the No. 3 center main journal.
Keep the probe away from the oil hole.
Preload the indicator approximately 0.050 inch.
Zero it.
Slowly rotate the crankshaft and observe the total variation.
The reference lists 0.00118 inch maximum production runout and states that a crank measuring less than approximately 0.001 inch is generally considered acceptable.
It’s a simple check.
And it’s considerably easier to discover a bent crankshaft sitting on V-blocks than after you’ve installed eight pistons, sealed the oil pan and dropped the engine into the car.
Funny how measuring things beforehand keeps ruining perfectly good engine-building disasters.
LS1 Crankshaft Runout FAQ
What is LS1 crankshaft runout?
It’s the measured deviation of the crankshaft from its rotational centerline as the crankshaft turns. The LS reference describes the test as an inspection for crankshaft bend.
Where do you measure LS1 crankshaft runout?
At the No. 3 center main journal while the crankshaft is supported by its front and rear main journals.
What is the LS crankshaft runout limit?
The reference lists maximum production runout at 0.00118 inch and says less than approximately 0.001 inch is generally acceptable during inspection.
How do you check LS1 crankshaft runout?
Support the crankshaft level, position a dial indicator at the center main journal, preload it approximately 0.050 inch, zero the gauge and slowly rotate the crankshaft while watching the reading.
Why should the dial indicator avoid the oil hole?
The source instructs positioning the probe slightly offset so the tip doesn’t cross the journal oil hole and distort the measurement.
Is crankshaft runout the same as crankshaft end play?
No. Runout evaluates straightness during rotation. End play measures forward-and-backward crankshaft movement.
Can an LS crankshaft with excessive runout be straightened?
Potentially, but the reference says straightening should only be performed by a skilled specialist and that not every crank can be successfully corrected.
