Chevy 350 Flexplate Torque Sequence Diagram
Chevy 350 flexplate/flywheel crisscross sequence with the cited L31 74 lb-ft branch, six-bolt pattern and balance/application checks.
For the cited 1998-1999 Chevrolet L31 5.7L application, tighten the six crank-to-flywheel/flexplate bolts in the factory sequence to 100 N-m (74 lb-ft). Hand-start all six, seat the plate in staged opposite-side passes, then complete the final pass. Do not extend 74 lb-ft to every vintage 350: pre-1986 two-piece-seal and 1986-up one-piece-seal cranks use different flange/balance parts, and aftermarket bolts specify their own lubricant and torque.
The flywheel or flexplate is both a rotating engine component and the connection to the clutch or torque converter. Uneven seating at the crank flange can create runout, starter-ring-gear problems, vibration or bolt fatigue. For the Chevy 350 Gen I / L31, the correct value is inseparable from crank flange, fastener, thread treatment and installed transmission hardware.
GM's late L31 service information specifies 74 lb-ft. That is a defensible application branch, not proof that a 1970 two-piece-seal crank, aftermarket flexplate and performance bolt use the same joint.
The interactive pattern alternates across the bolt circle to draw the part onto the crank flange evenly. It is a tightening controller, not a claim that every engine carrying the same family name has the same bolt count. Compare the actual flange, service illustration and replacement-part instructions before applying torque.
Interactive Chevy 350 Gen I / L31 crank-flange sequence
STAR PATTERN
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A 6-fastener opposite-side controller. Select 1 through 6; the physical labels around the circle are 1-4-2-5-3-6. Confirm that the installed flange matches.
Chevy 350 Flexplate Torque Sequence Diagram
| APPLICATION / ITEM | SPECIFICATION | NOTES |
|---|---|---|
| L31 crank bolts | 100 N-m / 74 lb-ft | 1998-1999 cited applications |
| Pattern | 6-fastener opposite-side | Confirm actual flange |
| Final authority | Exact vehicle or fastener sheet | Earlier 350s can differ |
| Converter bolts | Separate specification | Do not use 74 lb-ft |
A flexplate must match rear-main-seal generation, external balance requirement, ring-gear tooth count and converter bolt pattern.
How to use this specification correctly
- 01
Confirm the engine code, crankshaft/rear-seal generation, transmission type, flywheel or flexplate part number, balance specification and fastener part number. Photograph orientation marks before removal.
- 02
Disconnect the battery and support the engine and transmission with rated equipment. A flywheel is heavy and a thin flexplate has sharp edges; use eye protection and a flywheel holding tool rather than hands or a screwdriver jammed into the ring gear.
- 03
Remove the clutch/torque-converter fasteners and transmission according to the vehicle manual. Mark converter depth before separation and keep the converter fully seated in the transmission pump.
- 04
Inspect the crank flange, register, bolt holes, rear seal, pilot bearing, ring gear and both faces of the flywheel/flexplate. Reject cracks, heat checking beyond limits, elongated holes, damaged teeth or an unapproved resurfaced thickness.
- 05
Clean mating faces so the part seats metal-to-metal. Keep oil, grease and threadlocker off friction surfaces. Chase threads only if the service procedure permits it and blow blind holes clear without spraying solvent into the engine.
- 06
Position the plate with its offset and any weight in the documented direction. It should register cleanly on the crank without being pulled across burrs.
- 07
Apply the exact thread treatment, hand-start six matching bolts, snug in 1-4-2-5-3-6 order and complete the L31 final pass at 100 N-m.
- 08
Install clutch, pressure plate or converter hardware only after the crank-flange joint is complete. Use alignment dowels and the separate pressure-plate/converter torque specification.
- 09
Measure flywheel/flexplate runout where the manual requires it and rotate the crankshaft by hand. Verify starter engagement, converter freedom/endplay and bellhousing alignment before final installation.
- 10
After startup, stop for scraping, cyclic knock or abnormal vibration. Recheck accessible converter/inspection-cover work only by the application procedure; do not casually retorque sealed crank bolts after operation.
Selecting the correct application branch
GM's late L31 service information specifies 74 lb-ft. That is a defensible application branch, not proof that a 1970 two-piece-seal crank, aftermarket flexplate and performance bolt use the same joint.
A one-piece-seal 350 flexplate is not interchangeable with every earlier externally balanced or neutral-balance part. Verify crank flange, counterweight, tooth count and starter fit.
How the opposite-side sequence works
With 6 matching fasteners, the controller's physical labels are 1-4-2-5-3-6 around the circle. Tighten numerically so each step crosses or moves far from the previous position. Start every bolt by hand before the first staged pass.
Use several even preliminary passes when the source gives only a final torque, unless its instructions say otherwise. The final wrench pass must still follow the exact application sequence and calibrated range.
Installation procedure and verification
Position the plate with its offset and any weight in the documented direction. It should register cleanly on the crank without being pulled across burrs.
Apply the exact thread treatment, hand-start six matching bolts, snug in 1-4-2-5-3-6 order and complete the L31 final pass at 100 N-m.
Mistakes that cause repeat failures
- Installing the flexplate backward
- Mixing 153- and 168-tooth starter combinations
- Using a late L31 value on unknown early hardware
- Applying converter torque to crank bolts
- Ignoring cracks around converter or crank holes
Flywheel, flexplate and converter are separate joints
The crank bolts clamp the flywheel or flexplate to the crankshaft. Pressure-plate bolts clamp a clutch cover to a manual flywheel, while converter bolts connect an automatic flexplate to the torque converter. These fasteners commonly have different sizes, grades, thread treatments and torque values.
Never use the crank-flange torque for converter or pressure-plate bolts. Confirm converter seating before drawing the transmission to the engine; bellhousing bolts must not be used to force a gap closed.
Final installation checklist
- Correct balance and tooth count confirmed
- Orientation marks and crank register aligned
- New bolts/clamp ring used where required
- Mating faces clean and dry
- Specified thread treatment applied only to threads
- All bolts hand-started
- Staged opposite-side sequence completed
- Runout and pilot/bellhousing alignment checked
- Converter fully seated or clutch centered
- Engine rotates freely by hand
Chevrolet Chevy 350 Gen I / L31 specifications can change by model year, engine, platform, wheel, and installed component. Confirm the VIN or engine identity, part numbers, fastener condition, and the current manufacturer instructions before service.
Chevy 350 Flexplate Torque Sequence Diagram FAQs
What is L31 Chevy 350 flexplate bolt torque?+
The cited late production service information specifies 100 N-m (74 lb-ft).
How many crank bolts does a traditional Chevy 350 flexplate use?+
The matching traditional Gen I controller uses six; verify the actual crank flange and part before installation.
Should flywheel bolts be tightened in a star pattern?+
Use the exact numbered factory figure when available. An opposite-side or crisscross staged pattern is the safe controller for a matching circular flange because it seats the part evenly.
Can flywheel bolts be reused?+
Only if the exact service manual and fastener instructions permit reuse. Torque-to-yield, coated single-use or damaged fasteners must be replaced.
Is flywheel bolt torque the same as converter bolt torque?+
No. They are separate joints with different fasteners and specifications.
Technical sources
TorqueSheet favors engine- and component-specific manufacturer instructions over unsourced universal values.
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