383 Stroker Small Block Chevy - Stroker Cranks

Most 383 stroker cranks are designed to use external weights on the balancer and the flexplate/flywheel. Many aftermarket balancers now come with bolt-on external weights for these applications, like this Professional Products balancer.

Most 383 stroker cranks are designed to use external weights on the balancer and the flexp

Internal Vs. External Balance
Here's where it gets fun. When Chevy engineers pulled out their slide rules and put their pencils to the drawing board in the late '60s to design the 400ci small-block, it meant adding counterweight to the crankshaft to properly offset the longer stroke. There wasn't room in the crankcase to move the crank counterweights away from the crank centerline because the weights would hit the block. Instead, the designers added weight at the flywheel/flexplate and harmonic balancer ends of the crankshaft, creating an externally balanced engine. The 400 is the only Gen I small-block that requires offset balance weights on both ends of the crank. This means that most standard 383 rotator packages use an externally balanced crank that requires a 400-style offset weight balancer and flywheel/flexplate.

While externally balanced engines have survived for decades, heavy external weights are more likely to put a twist in the crank at higher engine speeds. To minimize this, many 383 cranks are also offered internally balanced. This requires Mallory, or heavy metal, to be added to the crank throws to offset the amount of weight normally added to the balancer and flywheel/flexplate. This is a more expensive process, but internal balance does offer durability advantages. Several crank manufacturers offer an internal balance option for 383 stroker packages either as separate cranks or complete rotator packages.

Internally balanced 383 packages require the addition of Mallory metal (a tungsten alloy) to the end crank counterweights. Holes are drilled in the crank, and heavy metal is added to increase the counterweight mass.
Internally balanced 383 packages require the addition of Mallory metal (a tungsten alloy)
In the case of a one-piece rear main seal 383 we built using a Lunati rotator package, this crank was designed to be internally balanced, which required a matching internally balance flywheel that no one makes. Note all the holes drilled to create this zero-balance flywheel.
In the case of a one-piece rear main seal 383 we built using a Lunati rotator package, thi
One-piece rear main seal cranks require an offset weight for use on a standard one-piece rear main seal application such as this flex-plate weight(arrow). If your one-piece 383 stroker crank is internally balanced, this weight must be removed or the engine will noticeably vibrate.
One-piece rear main seal cranks require an offset weight for use on a standard one-piece r

One-piece rear main seal stroker cranks also demand attention to a critical balance issue. A two-piece rear main seal crank has a small offset weight incorporated into the flywheel/flexplate flange that does not exist on one-piece rear main seal cranks. As a result, most one-piece rear main seal crankshafts require offset weight on the flywheel/flexplate. But since one-piece cranks have a unique flange bolt pattern, all one-piece flywheels/flexplates come with the required offset weight.

This is fine until you realize that several crank companies also offer internally balanced, one-piece rear main seal 383 stroker cranks. Balancing them requires eliminating the offset weight from the flywheel/flexplate. For flexplates, this means removing the weight that is usually welded in place. For flywheels, weight is not added but instead removed from the opposite side of the flywheel. Zero-balancing a one-piece flywheel means drilling holes 180 degrees from the original holes to zero-balance the flywheel and prevent vibration.

Two-Piece Vs. One-Piece Seals
From 1955 to 1985, all small-block Chevys were built with two-piece rear main seals. Unfortunately, this seal design is prone to leaking, so in 1986, GM redesigned the small-block with a one-piece rear main seal. This changed the rear crankshaft flange design to accommodate the one-piece seal. At first, no crankshaft companies were building one-piece performance stroker crankshafts, which required an adapter. However, all the major crank companies now offer 383 crankshafts in two-piece and one-piece rear main seal versions.

While the older two-piece crankshaft can be adapted for use in a newer one-piece block, the one-piece crank cannot be retrofitted to the two-piece block. That's just as well because there are some real advantages to using the one-piece rear main seal blocks to build a 383. We'll run through a quick version of a buildup of one of these engines, but the one-piece seal combined with the advantages of using a hydraulic roller cam in these same blocks is well worth the effort. It's important to know the one-piece crank also uses a smaller flywheel bolt pattern compared with the early two-piece design, so flywheels and flexplates do not interchange between these two flange designs.

One-piece rear main seal cranks require an offset weight for use on a standard one-piece rear main seal application such as this flexplate weight (arrow). If your one-piece 383 stroker crank is internally balanced, this weight must be removed or the engine will noticeably vibrate.
One-piece rear main seal cranks require an offset weight for use on a standard one-piece r
The amount of weight represented by this tiny counterweight on a two-piece rear main seal crank is what must be accommodated with a one-piece rear main seal flywheel or flexplate.
The amount of weight represented by this tiny counterweight on a two-piece rear main seal