JEGS Tech Specialist
Pete Mitchell
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
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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
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