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Main Stud Kit - 1989-1997 5.9L 12V Dodge Cummins
PART # SKU MP878
Verified Reviews
Original price
$277.61
-
Original price
$277.61
Original price
$277.61
$277.61
-
$277.61
Current price
$277.61
Availability:
in stock, ready to be shipped
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These are main studs, not head studs. Main and head studs serve different purposes—selecting the right one is crucial. These studs measure 14 mm. Before purchasing, please confirm that your vehicle is an early 1997 model or older, as they are not compatible with late 1997 models.
Why Main Studs?
Main studs provide superior clamping force compared to main bolts, reducing wear on block threads and assisting with main cap alignment. Unlike bolts, which twist during tightening, studs remain stationary, reducing the chance of main cap walking under high loads. They are especially beneficial in high-performance applications where increased stability and durability are required.
Disclaimer: Designed to secure crankshaft main bearing caps. This is NOT a head stud kit.
INSTALL GUIDE
This guide covers installation of the XOTIC PERFORMANCE™ MP878 main stud kit for the 1989–1998 5.9L 12V Dodge Cummins. Prefer a printable copy? Download the PDF manual.
Plan the align hone into the job. Swapping factory main bolts for studs changes how the caps are clamped, and the manual calls for an align hone done with the same fasteners and lubricant you'll use at final assembly, at the specified torque. On a 12V that has already seen thirty years of service, assume the bores need checking rather than hoping they don't.
Why a 12V Cummins needs main studs
The 12V is the engine that made the Cummins reputation: mechanical injection, no electronics to speak of, and a bottom end that will run forever at stock output. Nobody leaves them at stock output. A P-pump turned up, a 5x14 plate, and a bigger charger take an engine designed around 160 to 215 horsepower into three-figure-torque territory it was never specified for — and the cylinder pressure that makes that power travels down the rod and lands on the main cap on every power stroke.
Main cap fasteners are what keep the crankshaft bearing bores round and located under that load. Studs do it better than bolts for a structural reason: a bolt is torqued into the block, so it twists and stretches at the same time, while a stud is threaded in finger-tight and stays still while the nut is torqued against it — loading the stud in pure tension. That gives more consistent, more accurate preload, the tensile force in the fastener that becomes clamp force in the joint. Preload is what prevents cap walk and bore distortion. XOTIC PERFORMANCE™ main studs are manufactured from our premium XOTIC 7200 steel alloy and backed by a lifetime warranty.
What's in the MP878 kit
- 14 × M14 main studs (XOTIC 7200 alloy)
- 14 × hardened parallel washers
- 14 × nuts
- 1 × socket
- 1 × allen wrench
- 1 × fastener assembly lubricant
Before you start: verify first
Confirm that part number MP878 is compatible with your application before installing any components. Inspect all package contents for damage and clean as necessary to ensure accurate installation. Report any obvious defects or shipping damage to us before proceeding.
How to install main studs on a 12V Cummins
- Chase the block threads. Clean the threads in the block with a thread chaser prior to installing the studs, to ensure accurate fitment and precise torque readings. Chasing — not tapping — is the right operation: it cleans existing threads without cutting new material.
- Thread the studs in by hand. Screw the main studs in as tight as can be made by hand — no tool necessary, and do not apply torque. Loctite may be used for permanent stud installation, but the fasteners must be fully torqued before the Loctite sets.
- Check stud height with a straightedge. Use a straightedge ruler to measure the distance from the mating surface (deck or main cap) to the top of each installed stud. Ensure all studs of the same length group sit level with each other (within 1 mm / 0.040”). Uneven height may indicate debris or incorrect thread engagement. Properly installed studs will bottom out smoothly and show uniform height across all positions. If a stud appears higher or lower than the others, remove it, re-clean the hole, and reinstall by hand. Do not use tools to force studs deeper. Incorrect stud seating can cause off-angle stress, uneven preload, or stud fracture during engine operation.
- Install the main caps. Set the caps in place and ensure appropriate alignment before any load goes on them.
- Lubricate. Using the fastener assembly lubricant included in the package, lubricate the threads of the main studs and the nuts.
- Hand-tighten the nuts. Thread the nuts onto the studs as tight as can be made by hand.
- Torque in three equal steps. Working in the sequence shown in the manual's torque sequence diagram, tighten the nuts through the three stages below. Never go straight to the final value.
- Align hone. Perform an align hone with the same fasteners and lubricant that will be used during final assembly, at the specified torque, to ensure optimal bearing clearance.
12V Cummins main stud torque specs
| Stage | Torque |
|---|---|
| 1 | 55 ft-lbs |
| 2 | 110 ft-lbs |
| 3 (final) | 175 ft-lbs |
A common mistake to avoid: when torquing a fastener, do not stop short of the recommended value — continue in one motion until the specified torque is achieved. If you accidentally stop short, loosen the fastener and re-torque. Stopping short and "topping up" produces unequal preload distribution across the caps and can leave a bore out of round.
Frequently asked questions
What are the main stud torque specs for a 12V Cummins?
55 ft-lbs, then 110 ft-lbs, then a final 175 ft-lbs — three equal steps, following the sequence in the manual.
Does MP878 fit a 24V Cummins?
No. MP878 covers the 1989–1998 5.9L 12V. For the 1998.5–2006 24V, see the MP876 kit and guide.
Do I need to align hone after installing main studs?
The manual calls for one. Studs clamp the caps differently than the factory bolts did, so the main tunnel needs checking and, in most cases, correcting. Do the hone with the same studs, nuts, and assembly lubricant you'll use for final assembly, torqued to spec.
Should the studs be torqued into the block?
No. Thread them in finger-tight only. Torquing a stud into the block twists it while it's being stretched, which is exactly what running studs is meant to avoid.
While you're in there
A 12V apart far enough for main studs deserves the same hardware at the deck and the rods. See our 12V Cummins head stud guide (CP878) and the 5.9L connecting rod bolt kit (CP114).
Need help?
For technical support, email support@xotic-performance.com. All XOTIC PERFORMANCE™ fasteners are covered by our limited lifetime warranty. Finished your install? Tag #XOTICPERFORMANCE on Instagram for a chance to be featured.
© 2026 XOTIC PERFORMANCE™. This installation guide is an original copyrighted work of XOTIC PERFORMANCE™. Reproduction, distribution, or use of this content in whole or in part without written permission is prohibited. Doc ref: 2025.05.20 (web edition 2026.08).
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