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When selecting a flexplate/flywheel or a harmonic balancer/damper, it is important to know if it needs to be balanced or unbalanced before purchase and installation. An incorrect part will result in an un-balanced engine as well as severe damage to it. Below is a "cheat sheet" that will help you to know if the engine you are working on was balanced or unbalanced from the factory.
NOTE: If the crankshaft or rotating assembly in your engine has been upgraded, you will need to directly confirm with the manufacturer if it is balanced or unbalanced before purchasing the damper or flexplate/flywheel rather than using the below list.
Small Block Chevrolet
- Gen1 - 1986 and Prior (267/283/302/305/327/350) - Internal balance
- 400 SBC - External balance
- 1987-1995 (Includes LT1/LT4 Opti-spark) - Internal balance front / External balance rear
- 1996-2000 - Internal balance front / External balance rear
- LS Engines - Internally balance
- LT Engines- (2016+ model year) Internal balance
Big Block Chevrolet
- W Series / MK I (348-409) - Internal balance
- MK IV 396-427 - Internal balance
- MK IV 454-502 - External balance
- GEN V 572 - Internal balance
GEN VI
- L29/L21 - External balance
GEN VII
- L18 Vortec 8100 - Internal balance
Pontiac
- 326-455 - Internal balance
Oldsmobile
- 260-307-330-350-400-403-425-455 - External balance
AMC
Gen 1 (1965 and prior)
- 250-287-327 - External balance
Gen 2 (1966-1970)
- 290-343-390 - External balance
Gen 3 (1970-1991)
- 304-360-390-401 - External balance (Though they share the same crank flange, 304, 360, and 401 do not interchange)
Small Block Chrysler
- 318 A (POLY) - Internal balance
- 273-318-340 (340 to 1971 Steel Crank) LA - Internal balance
- 340 (1972 up w/Cast Crank) - External balance
- 360 - External balance
Chrysler Magnum
- 318 (5.2) Internal balance
- 360 (5.9) External balance
- 5.7 L, 6.1 L, 6.2 L, 6.4 L HEMI - Internal balance
Big Block Chrysler
B Engines
- 1958-1971 (forged crank) - Internal balance / 1972-1978 (cast crank) - External balance
- 350-361-383 - Internal balance
- 400 - External balance
RB Engines
- 1958-1971 (forged crank) - Internal balance, 1972-1978 (cast crank) - External balance
- 383-413-426- Internal balance
- 426 Wedge- Internal balance
- 440 (1966- 1971 with forged crank) - Internal balance
- 440 (1972- 1978 with cast crank) - External balance
- 440 "Six Pack" (with forged crank and heavy rods) - External balance
- 426 HEMI - Internal balance
Small Block Ford
- 289-302 - External balance - 28 ounces
- 302 HO - External balance - 50 ounces
- 351W - External balance - 28 ounces
- 351C - External balance - 28 ounces
- 351M/400 - External balance - 28 ounces
Big Block Ford
- 429-460 - Internal balance
Ford Y Block
- 239-256 (1954 Cars Only- Cleveland Blocks) - Internal balance
- 272-292-312 - External Balance
- 239-256 (Trucks only- Dearborn Blocks) - External balance
Ford FE Block
- 332-352-360-390-406-427- Internal balance
- 410- External balance
- 428- External balance
- 330-361-391- External balance
