Bolt torque sequence: star and crisscross patterns, in stages
Tighten a multi-bolt joint in a crisscross or star pattern, in at least two passes: run every bolt down snug, bring all of them to an intermediate torque, then to final torque in the same order. Bolts tightened first lose preload as their neighbors pull the joint together, and the passes even it out.
Contents8 sections
Key takeaways
- Bolts tightened first relax as the rest pull the joint down; in some joints this can virtually eliminate their tension 1.
- Alternate between fasteners so parts aren't distorted, and finish the whole pattern at each stage before going to the next 2.
- NASA's standard calls for a torque sequence with incremental torquing wherever an even clamp load matters 3.
- Where the maker prints a numbered sequence, follow it exactly, including the order of every pass 4 5.
Why the order matters
A bolt is a stiff spring. Tighten one bolt in a flange to full torque and it clamps the parts that are under it. When you tighten the next one, the joint compresses a little more, and the first bolt loses some of its stretch. Fastenal describes exactly this: bolts tightened first relax as the joint is further compressed by the rest, and “in some cases, this can virtually eliminate our bolt tension” 1. Creep and flow at heavily loaded thread and joint surfaces add to the loss 1.
Two things follow:
Spread the load
Working across the joint instead of around it keeps one side from closing before the other, which is what distorts covers, flanges and heads.
Come back
A second and third pass at rising torque recovers the preload the early bolts lost.
GM puts it in one sentence for wheel nuts and cylinder head bolts alike: tighten “by alternating between the fasteners to ensure the parts are not distorted and that the fasteners are torqued evenly”, and only once every bolt has reached a minimum torque, tighten them completely to specification 2. NASA-STD-5020B says that when an evenly distributed clamp load is important, “an appropriate torque sequence along with incremental torqueing should be specified” in the drawing or procedure 3.
The basic procedure
When the equipment maker gives no sequence, the sources above agree on this outline:
Run all fasteners down by hand
Every bolt in its hole, every nut started, before any is tightened. RCSC requires bolts in all holes before compacting a structural joint 6.
Snug in pattern
Bring each fastener to light contact in a crisscross order. Snug is not a torque value, it is “firm contact” of the parts 6.
Intermediate pass
Go round the same pattern to a fraction of final torque. The makers’ procedures below use two or more steps.
Final pass
Same pattern, full torque.
Check pass
Go round once more at final torque. Any fastener that turns had lost preload.
Subaru’s revised procedure for a two-bolt stabilizer bracket shows the shape of it even at its smallest: snug the front bolt then the rear, torque the front to 35 N·m (25.8 ft-lb) then the rear, then “re-check both bolts in the same sequence for proper torque” 7.
Star and crisscross patterns
The idea is to make each move cross the joint.
- Even number of bolts on a circle (4, 6, 8, 12…). After each bolt, go to the one directly opposite, then a quarter turn round the circle and across again.
- Odd number on a circle (5). Skip one bolt each move. On five studs that traces a five-pointed star: 1, 3, 5, 2, 4.
- Rows of bolts (heads, covers, manifolds). These have numbered or lettered orders in the service information, and they are rarely a simple star. Use the maker’s diagram.
On structural joints RCSC sets the direction differently: both snugging and pretensioning start “at the most rigidly fixed or stiffest point” and work systematically out toward the free edges 6. More than one cycle through the bolt pattern may be needed just to reach snug-tight 6.
Wheel makers print the pattern in owner’s manuals. Ram’s manual says to “Tighten the lug nuts/bolts in a star pattern until each nut/bolt has been tightened twice” and draws the pattern for four, five, six and eight lugs 8. Tesla’s service manual tightens the five lug nuts “in a criss-cross star pattern” to an initial torque, then again to the final 175 N·m (129 ft-lb) 9. The lug nut tightening guide covers wheels in detail.
How manufacturers write sequences
Engine procedures show how much detail a real sequence carries. Two examples, quoted from dealer documents:
| Stage | FCA (Pentastar head, ZD2 notification) 4 | Subaru EJ25 STI (bulletin 02-179-18) 5 |
|---|---|---|
| Prep | Clean bolt holes; do not add oil to bolt threads | Clean threads and holes; coat threads and washers with engine oil |
| 1 | All to 30 N·m (22 ft-lb), in sequence | All to 40 N·m (29.5 ft-lb), A to F |
| 2 | All to 45 N·m (33 ft-lb) | All to 69 N·m (50.9 ft-lb), A to F |
| 3 | Re-tighten all to 45 N·m | Loosen all 180°, then another 180°, F to A |
| 4 | All + 125° | Repeat 40 N·m, then 69 N·m |
| Then | Loosen all in reverse, repeat at 30/45/45 N·m, then + 130° | Loosen and re-tighten bolts in groups, finishing with angle steps (for example 98 to 102°) |
Several things stand out. FCA says “The torque sequence must be used for each step” 4. Both procedures loosen the bolts in reverse order partway through and repeat the torque steps before the final angle. The two makers disagree on oil: FCA says not to add oil to the bolt threads, Subaru says to coat them thoroughly 4 5. Each is right for its own engine, because its torque values were set with that thread condition. Subaru also warns that if bolts make a stick-slip sound or don’t tighten smoothly, you start again from cleaning 5.
FCA adds a reason to clean blind holes before any sequence: oil, coolant or sealant left in a bolt hole is non-compressible and can crack an aluminum casting when the bolt is tightened 4.
Stages with angle steps
Torque-plus-angle bolts follow the same discipline. GM: all fasteners are tightened to the torque value on the first pass, then each receives the specified angle on the second, and sometimes more than two passes are needed 2. The angle is applied relative to the mating fastener or surface, with a backup wrench if the mating part could turn 2. Many of these bolts are single-use: see torque-to-yield bolts.
Mistakes that undo a sequence
- Tightening one bolt to full torque first. It will lose preload as the rest come down, and the part may rock or distort.
- Going around the circle. Neighbor-to-neighbor tightening closes one side of the joint first.
- Skipping the check pass. The early bolts are the ones that lose tension. A final pass at full torque catches them.
- Changing the thread condition. A sequence written for oiled threads does not hold for dry ones, and the reverse. See dry vs lubricated torque.
- Using a sequence from a different engine or part. Bolt order, angles and even the loosen-and-repeat steps differ between makers. When the maker gives a sequence, it overrides any generic pattern, including this one.
Sources
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Spotted a value that doesn’t match its source? Report an error
Related
- Lug nut tighteningTighten lug nuts in a star pattern, in two passes, on clean dry studs, then re-check when your manual says: 25 miles for Ram, 100 for Ford, 600 for Nissan.
- Torque-to-yield boltsTorque-to-yield bolts are tightened by torque plus angle into permanent stretch. How to read a TTY spec, apply the angle, and when GM, FCA and Honda say to replace them.
- Torque vs tensionTorque only estimates bolt tension: about 90% goes into friction, so preload scatters ±25% or more. The figures from NASA-STD-5020B, NASA RP-1228, Fastenal and RCSC.
- Joint typesRCSC 2020 joint types: when a structural bolted joint may be snug-tightened and when it must be pretensioned or slip-critical, with install and inspection rules.