Crankshaft end play is one of those measurements that’s easy to overlook during an LS1 build because the crankshaft can rotate perfectly well even when something isn’t right.
Rotation isn’t the only direction the crankshaft can move.
The crank can also move slightly forward and backward inside the block. That axial movement is crankshaft end play, and on an LS1 it is controlled at the crankshaft’s thrust-bearing position.
According to the LS engine-building reference, OEM LS crankshaft end play is:
0.0015–0.0078 inch
The same reference identifies the center No. 3 main position as the thrust location.
That tiny amount of movement is intentional. The goal isn’t zero end play. The goal is controlled clearance.
What Is LS1 Crankshaft End Play?
Crankshaft end play is the total amount the crankshaft can move longitudinally—or front to rear—inside the engine block.
This is different from crankshaft runout.
End play measures axial movement along the crankshaft’s centerline.
Runout evaluates whether the crankshaft is bent as it rotates.
They’re two completely different measurements, even though both can involve a dial indicator.
The LS reference lists OEM crank end play at 0.0015–0.0078 inch and separately discusses checking crankshaft runout at the center main journal.
What Is the LS1 Crankshaft End-Play Specification?
The LS engine reference specifies:
| Measurement | OEM LS Specification |
|---|---|
| Crankshaft end play | 0.0015–0.0078 in. |
| Main journal diameter | 2.558–2.559 in. |
| Main bearing clearance | 0.0007–0.00212 in. |
| Thrust-wall width | 1.029–1.032 in. |
| OE LS1/LS6 stroke | 3.622 in. |
These dimensions are provided in the reference’s OEM LS crankshaft specifications.
For this FAQ, however, the number to remember is:
0.0015–0.0078 inch of crankshaft end play.
Don’t confuse that specification with main-bearing oil clearance. They describe different relationships inside the rotating assembly.
Where Is the LS1 Thrust Bearing Located?
The LS architecture places the crankshaft thrust surface at the center, or No. 3, main-bearing position.
That’s the middle main bearing of the five-main-bearing arrangement.
The LS reference’s GM parts information reinforces this distinction. For LS engines other than the LS7 and LS9, it identifies:
GM 88894271 — main bearing for positions 1, 2, 4 and 5
GM 89017572 — main thrust bearing for position 3.
So the No. 3 bearing isn’t simply another copy of the other four main bearings. It performs the additional job of controlling crankshaft axial movement.
Why Does an LS1 Need Crankshaft End Play?
An assembled engine can’t simply clamp the crankshaft between two thrust surfaces with zero clearance.
The crankshaft must be able to rotate without the thrust surfaces being permanently bound together.
That means a controlled amount of axial clearance is necessary.
Too little movement and the assembly doesn’t have the specified clearance.
Too much movement means the crankshaft is traveling farther axially than the reference specification allows.
This is why end play should be measured, rather than judged by grabbing the crank snout and deciding that it “feels about right.”
Human fingers make surprisingly poor precision measuring instruments.
How Do You Measure LS1 Crankshaft End Play?
Crankshaft end play is normally checked using a dial indicator capable of reading the small amount of axial movement involved.
With the crankshaft installed and the relevant main-bearing assembly properly secured, position the dial indicator so its plunger measures movement parallel to the crankshaft’s axis.
The basic measurement is the difference between the crankshaft’s two axial extremes:
- Move the crankshaft fully in one axial direction.
- Zero the dial indicator.
- Move the crankshaft fully in the opposite axial direction.
- Read the total movement shown by the indicator.
That total movement is crankshaft end play.
For the OEM LS specification provided by the source, you’re comparing that measurement against 0.0015–0.0078 inch.
The supplied LS reference establishes the specification but does not provide a complete factory service-manual procedure for measuring LS1 end play, so the method above describes the standard dial-indicator measurement principle rather than claiming to reproduce a GM service procedure.
Where Should the Dial Indicator Be Positioned?
The indicator needs to measure axial crankshaft movement, not rotational movement or radial runout.
A common approach is to mount a magnetic indicator base securely to the engine and place the indicator tip against a suitable crankshaft surface where forward-and-rearward movement can be measured accurately.
The exact mounting arrangement can vary depending on whether you’re dealing with a bare short block, an engine stand or a more complete assembly.
The important part is alignment.
If the dial indicator isn’t positioned to accurately follow the crankshaft’s axis, the reading can incorporate movement you aren’t actually trying to measure.
When you’re dealing with thousandths of an inch, “close enough” starts becoming expensive.
Is Crankshaft End Play the Same as Main-Bearing Clearance?
No.
This distinction is important because both specifications appear in the LS crankshaft data.
The reference lists main-bearing clearance at 0.0007–0.00212 inch while crankshaft end play is 0.0015–0.0078 inch.
Main-bearing clearance relates to the running clearance between the crankshaft main journals and bearings.
Crankshaft end play describes the crankshaft’s allowable front-to-rear axial movement.
One measurement doesn’t substitute for the other.
Is Crankshaft End Play the Same as Crankshaft Runout?
No.
Runout determines whether a crankshaft deviates as it rotates.
The LS engine reference describes placing the crankshaft on level V-blocks or a crankshaft polishing station and positioning a dial indicator at the center No. 3 main journal. The crankshaft is then slowly rotated while runout is observed. The reference states that runout below 0.001 inch is generally considered acceptable, while a crank at or above that level requires straightening or replacement according to its described inspection procedure.
End play doesn’t require rotating the crankshaft to determine how straight it is.
Instead, you’re measuring how far the entire crankshaft can travel axially.
Same dial indicator. Very different question.
What Does the No. 3 Main Bearing Actually Do?
All five main-bearing positions support the crankshaft, but the No. 3 location has the additional thrust-control function identified by the LS reference.
Its thrust surfaces restrict how far the crankshaft can move forward or rearward.
That makes the condition and dimensions of the thrust area important during an engine build.
The OEM LS crankshaft specifications in the reference list a thrust-wall width of 1.029–1.032 inches.
Again, that’s not the end-play specification. It’s another dimensional specification associated with the crankshaft.
The actual end-play measurement remains 0.0015–0.0078 inch.
What If LS1 Crankshaft End Play Is Too Tight?
If the measured end play is below the specified range, don’t simply assume the parts will “wear in.”
Something in the assembled relationship needs to be checked.
Start by confirming that the measurement itself is accurate and that the crankshaft is actually moving between its full axial limits.
From there, the thrust-bearing installation, bearing condition, crankshaft thrust surfaces and relevant dimensions deserve inspection.
The supplied LS reference provides the dimensional specification but does not prescribe a troubleshooting sequence for below-specification end play, so the cause shouldn’t be diagnosed from the measurement alone.
Measure first. Inspect second. Grind random engine parts never.
What If LS1 Crankshaft End Play Is Too Large?
The same logic applies to excessive end play.
A measurement greater than the source’s 0.0078-inch upper specification means the assembly is outside the provided OEM LS range.
That warrants inspection of the thrust-bearing area and crankshaft rather than simply continuing assembly.
If you’re rebuilding an unknown used engine, this is precisely why checking end play before finishing the build is valuable.
Discovering a dimensional problem while the engine is on a stand is annoying.
Discovering it after the engine is installed is character building.
Should You Check End Play With a New Crankshaft?
Yes.
New components don’t eliminate the need for measurement.
An engine is an assembly of parts, and the finished clearances are what matter.
This becomes especially relevant with performance LS builds where the crankshaft, bearings and block may not all be the original production components.
The LS reference documents numerous aftermarket crankshaft combinations as well as factory crankshaft specifications. It also emphasizes inspecting crankshafts for dimensions, runout and defects during the engine-building process.
A part being new tells you its age.
A dial indicator tells you its clearance.
Don’t Confuse LS1 End Play With Camshaft End Play
There’s another potential source of confusion in LS specifications.
The reference separately lists camshaft end play at 0.001–0.012 inch in its engine specifications.
That’s not the crankshaft specification.
For the crankshaft, the OEM LS figure provided by the reference is:
0.0015–0.0078 inch
Keeping those two specifications separate is particularly important when collecting measurements during a complete engine build.
Check Crankshaft End Play Before Finishing Your LS1 Build
Crankshaft end play isn’t particularly glamorous.
It doesn’t add horsepower, make boost noises or generate an impressive parts list.
It does tell you whether one of the fundamental clearances in the rotating assembly falls within the specification provided for the LS crankshaft.
For an LS1, the reference gives us three key facts:
Crankshaft end play: 0.0015–0.0078 inch
Thrust location: No. 3 center main
OE LS1/LS6 crankshaft stroke: 3.622 inches
Measure it while you have access to the engine.
It’s considerably easier to reposition a dial indicator than pull an LS1 back out of a car.
LS1 Crankshaft End Play FAQ
What is the correct LS1 crankshaft end play?
The supplied LS engine-building reference specifies OEM LS crankshaft end play at 0.0015–0.0078 inch.
Where is the LS1 thrust bearing located?
The thrust-bearing location is the No. 3 center main position.
What is the LS1 main thrust-bearing part number?
The reference lists GM 89017572 for the No. 3 thrust position on LS engines other than the LS7 and LS9.
How do you check LS1 crankshaft end play?
Use a dial indicator to measure the crankshaft’s total axial movement between its forward and rearward limits. The supplied reference establishes the clearance specification but does not provide a complete factory service-manual measurement procedure.
Is LS1 crankshaft end play the same as main-bearing clearance?
No. The reference lists crank end play at 0.0015–0.0078 inch and main-bearing clearance separately at 0.0007–0.00212 inch.
Is crankshaft end play the same as crankshaft runout?
No. End play is axial movement. Runout evaluates crankshaft straightness as the crankshaft rotates.
