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Old 08-20-2010, 03:46 AM
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Waldo, if you're convinced the vibration is due to the crank/rods and piston mismatch, the best route for you is to just rebalance the crank in the normal way, IMHO.

To do anything to the crank involving balancing will require (in your case) removing weight, and this requires the crank to be removed to do the necessary machining ops. So if the crank needs to come out anyway, the weighing of the piston and rod, rings, bearings, etc.- to get the actual and not a theoretical bobweight- is a small additional effort to get it right and not just close.

That is, unless you were somehow planning on balancing the counterweights w/the crank in the engine...

In any event, possibly the following will be of some use to you:

IDENTIFYING ONE PIECE REAR MAIN SEAL CRANKSHAFTS
GM 5.0 & 5.7L (305 & 350 CID) Crankshafts

Identifying the Chevrolet 5.0 & 5.7L (305 & 350 CID) crankshaft used in various GM cars and trucks has not been made any easier since the introduction of the one piece rear main seal crankshaft.

Currently AERA is aware that casting numbers 14088526 and 14088535 are cast iron crankshafts used in either 5.0L (305 CID) or 5.7L (350 CID) engines. Again, GM is using the same crankshaft castings in two differently balanced engines. A steel crankshaft with the forging number 14088532 is used in the 5.7L (350 CID) Corvette engines.

Both engines are externally balanced and use the same counterweighted flexplate or flywheel and a non-counterweighted damper. Equally shared are the connecting rods which weigh 603-604 grams. The rotating (big) end of the connecting rod weighs 424 +/- 2 grams while the reciprocating (pin) end weighs
179 +/- 2 grams.

The weight for a 5.0L (305 CID) piston and pin is 646 +/- 3 grams, whereas a 5.7L (350 CID) piston and pin come in at 743 +/- 3 grams. The total bob weight for the 5.0L (305 CID) engine is 1815 grams in comparison to the 5.7L (350 CID) engine at 1916 grams.

AERA mrmbers have visually differentiated the crankshafts by the balance holes drilled into the front and rear counterweights. Machinists using these specifications should be aware that all of the measurements are approximate and may vary slightly from crankshaft to crankshaft.

The holes drilled in the 5.0L (305 CID) crankshaft front counterweight vary somewhat. There are either two 1 holes drilled to a combined depth of 2.563, or two similarly drilled 1 holes along with a third .750 hole drilled to a depth of
.125-.313. The rear counterweight is much the same with either two 1 holes drilled to a combined depth of 2.250, or two similarly drilled 1 holes along with a third .750 hole drilled to a depth of .188-.313

The 5.7L (350 CID) crankshaft's front counterweight has two 1 holes drilled to a combined depth of 1.188. The rear counterweight also has two 1 holes drilled to a combined depth of 1.563.

To-date visually separating the crankshafts using the specifications outlined above has been validated by later balancing.
The AERA Technical Committee
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