Jun 1, 2016 | OTHER SHOP WORK

Car Shop Tips

It is a common practice to use the early Chevrolet V8 6-1/8” diameter harmonic damper as a light weight performance upgrade to the 6-3/4” and the 8” dampers that come on the later, longer stroke engines. Though no horsepower is to be had by lightening the rotating mass, quicker acceleration of the engine is reported. Caution must be taken when doing this mod, and it may not be the fault of the cautious engine builder, but of the DIY’er who makes the change to the engine on his own. The timing mark on the early (1967 and older) balancer is 12 degrees off from the later (1968-on) engines. If a different timing marker is not used on the timing cover, this can be enough to cause serious damage to the engine. An additional 12 degrees of advance, on top of what might be an out of tune motor, will cause severe detonation and damage to pistons, rings, valves and rod bearings. There was a 6-1/4” balancer used on the 327 engines in some G-series vans around 1968 and 69, that does have the correct markings, but these are very hard to find. Aftermarket performance 6-1/8” diameter dampers all seem to have the 1968-on timing mark placement, which potentially could cause a problem if used in an early application. It should also be noted that General Motors went to an 8” balancer on all of their high performance small block V8’s for a reason. Cracked crankshafts and several other harmonic or vibration induced problems have been reported on engines running small dampers, that seem to have been corrected when changing back to the heavier, larger diameter units.

Engine Pro Technical Committee.

June, 2016