When you’re assembling an LS1 short block, the main caps aren’t parts you want to install using the highly technical method known as “that looks about right.”
The LS engine uses five main-bearing caps, and the LS engine-building reference identifies two important pieces of information on the caps: their main-bearing location and their direction.
According to the reference, each cap is marked for its position—1, 2, 3, 4 or 5—and for direction, with the arrow pointing toward the front of the engine.
That makes main-cap orientation relatively straightforward once you know what you’re looking for.
Which Way Do LS1 Main Caps Face?
The basic rule from the LS engine-building reference is:
Install each main cap in its numbered location with the arrow pointing toward the front of the engine.
The book specifically instructs the builder to pay attention to both location and direction when positioning the main caps.
So there are two things to verify before seating a cap:
Correct numbered position and correct front-to-rear orientation.
Getting one right doesn’t compensate for getting the other wrong.
How Many Main Caps Does an LS1 Have?
The LS arrangement described in our engine-building reference uses five numbered main locations: 1, 2, 3, 4 and 5.
These caps support the crankshaft in the block.
During assembly, don’t treat the five caps as an anonymous pile of similar-looking parts. Their markings provide the information needed to return them to their intended locations and orient them correctly.
A simple organization system on the workbench can prevent a surprisingly annoying mistake later.
What Do the Numbers on LS1 Main Caps Mean?
The numbers identify the cap’s bearing location.
The reference explicitly describes each main cap as being marked for bearing location:
1, 2, 3, 4 and 5.
Before seating the caps, identify those markings and arrange the caps in sequence.
This is particularly useful if the engine has already been disassembled and the caps are sitting separately from the block.
Don’t rely entirely on visual similarity.
Use the identification provided on the parts.
What Does the Arrow on an LS1 Main Cap Mean?
The arrow establishes the cap’s directional orientation.
According to the reference:
The arrow points toward the front of the engine.
That’s the critical piece of information if you’re staring at a bare LS block wondering which way a cap should face.
Find the cap’s location number.
Find its directional arrow.
Put it in the corresponding main location with the arrow toward the front.
No interpretive dance required.
Where Is the Front of an LS1 Engine?
For purposes of main-cap orientation, “front” means the front/timing-drive end of the engine.
That’s the end of the block associated with the crankshaft snout and front engine cover.
So when the PDF says the main-cap arrow faces forward, orient the arrow toward that end of the engine.
This article intentionally isn’t turning that into a discussion of timing components. The important point here is simply establishing a consistent reference for main-cap direction.
How Should an LS1 Main Cap Be Positioned Before Seating It?
The reference recommends initially positioning the cap as closely as possible by eye.
When using main-cap bolts, it then describes loosely installing the four primary 10mm main-cap bolts, engaging them only a few threads. These fasteners help guide the cap into its proper register.
If main studs are being used instead, the installed studs perform that guiding function.
This is a positioning step.
It isn’t the final tightening procedure, and it shouldn’t be confused with the LS1 main-cap torque sequence.
That’s deliberately outside the SEO scope of this FAQ.
Should You Force an LS1 Main Cap Into the Block?
The reference describes aligning the cap with the fasteners and then pushing it against the block before using a clean plastic mallet to roughly seat the cap.
That wording matters.
It doesn’t describe attacking the cap with a steel hammer until the engine recognizes who’s boss.
The cap should first be correctly identified, correctly oriented and aligned with its register.
The plastic mallet is then used as described to help seat it.
What Is Special About the No. 3 LS Main Location?
The No. 3 center main is also the LS engine’s thrust-bearing location.
That’s useful identification information, but it shouldn’t change the SEO focus of this article.
Pro Street’s separate LS1 crankshaft-end-play FAQ covers thrust clearance and the No. 3 thrust-bearing function in detail.
For main-cap orientation, the takeaway is simply that No. 3 belongs at the center main position and, like the other caps, its directional marking needs to face correctly.
Is Main Cap Orientation the Same as Main Bearing Orientation?
No.
This is an important distinction because both operations occur in essentially the same area of the engine.
Main-cap orientation concerns which numbered cap belongs at each location and which direction that cap faces.
Main-bearing-shell orientation concerns how the bearing shells are positioned inside the block saddles and caps.
The PDF specifically notes that upper main-bearing shells contain an oil hole that aligns with the block’s main-bearing oil-feed hole, while the lower bearing shells don’t have those oil holes.
That’s a separate assembly issue.
For this FAQ, we’re concentrating on the caps themselves.
Do LS1 Main Cap Arrows Point Forward or Rearward?
Forward.
The LS engine-building reference specifically states that each cap is marked for direction with the:
“arrow towards front.”
That’s probably the most useful answer on this entire page for someone standing over an upside-down engine block.
It also explains why the markings matter.
When an engine is inverted on a stand, the visual orientation can become less intuitive than it is when the engine is sitting normally in the vehicle.
Follow the cap markings rather than trying to remember how everything looked before disassembly.
Can LS1 Main Caps Be Installed in Any Position?
The supplied source doesn’t treat the caps as interchangeable positions during assembly.
Instead, it specifically instructs the builder to pay attention to each cap’s marked bearing location—1 through 5—and direction.
That’s the procedure this FAQ follows.
I wouldn’t extend that statement into claims about replacing an individual cap from another engine or correcting a mismatched cap without additional machine-shop information. The section we’re using doesn’t establish those procedures.
If you’re dealing with missing, damaged or mismatched caps rather than simply reinstalling the engine’s original components, that’s a different question.
Should You Check the Main Cap Markings Before Installing the Crankshaft?
Organization should begin before final assembly.
Once you’ve identified the markings, arrange the caps in their correct sequence and verify the directional arrows.
When the crankshaft and caps are ready for assembly, you aren’t then trying to decode five pieces of iron while simultaneously protecting freshly prepared bearing surfaces.
The reference also emphasizes care when lowering the crankshaft onto the upper main bearings. Once positioned, it says not to rotate the crankshaft at that stage.
Preparation makes that process considerably less chaotic.
LS1 Main Cap Orientation Quick Reference
For an LS1 main-cap installation based on the supplied engine-building reference:
Main-cap locations: 1 through 5
Directional marking: Arrow
Arrow direction: Toward the front of the engine
Center main: No. 3
No. 3 additional function: Thrust-bearing location
Initial cap alignment: Position correctly and use the primary fasteners or installed studs to help guide the cap
Initial seating: The reference describes carefully seating the aligned cap with a clean plastic mallet.
The most important rule is wonderfully uncomplicated:
Match the number. Point the arrow forward.
LS1 Main Cap Orientation FAQ
Which way do LS1 main caps face?
Install the caps with their directional arrows pointing toward the front of the engine, according to the LS engine-building reference.
Are LS1 main caps numbered?
Yes. The reference describes the main caps as marked for bearing locations 1, 2, 3, 4 and 5.
What does the arrow on an LS1 main cap mean?
It indicates orientation. The arrow should point toward the front of the engine.
Which LS1 main cap is the center cap?
The No. 3 main occupies the center position. It’s also the thrust-bearing location in the LS arrangement described by the reference.
Can I identify LS1 main-cap direction by looking at the cap?
Use the identification markings described by the source: the cap’s location number and directional arrow. Don’t rely solely on the cap’s general appearance.
Do the LS1 main-cap arrows point toward the transmission?
No. The source explicitly says the arrows point toward the front of the engine.
Is main-cap orientation the same thing as main-bearing orientation?
No. Cap orientation identifies the cap’s numbered location and direction. Bearing-shell orientation concerns correct positioning of the bearing shells, including alignment of the upper bearing oil holes with the block’s oil-feed passages.
