split head 200 Balancing question

[TTracing]

Anyone know if all the split head 200 6 cyl flat head components ( Pressure plate, flywheel, crank, pulley )  are 0 balanced ?????

 

I have a vibration issue and the only thing I see that is odd some previous owner replaced the original Pressure plate with a newer style GM

 

any thoughts would be welcome.

 

Bill

[Bloo]

I don't know. On my 1936 208, I found paint marks indicating clocking. That implies that at least those 2 parts were probably balanced together, and that replacing the pressure plate would require re-balancing the flywheel at the very least. Worst case would be that Pontiac put the crank, balancer, flywheel, and pressure plate all in the balancer together, and you would have to have all those parts back out of the car. Ugh. I hope not.

 

"External Balance" is not out of the question on a straight six, but it is highly unlikely in my opinion. Straight sixes are naturally in first order balance, and so it is just a question of balancing all the parts. There is typically no need for off center counterweights so large that they would not fit inside the engine, as sometimes occurs with V8s and other engine configurations.

 

The 200s are old enough that balancing was not done by every manufacturer. I don't know exactly when Pontiac started. Even if the engine was in balance when it left the factory, the rods were still babbitted on the 200s, and it was common in those days to replace just one rod (or piston) from a parts store after some failure. You could easily have parts that no longer match in weight.

 

There is normally no issue of "total weight" of a rod and piston assembly vs crank balancing on straight sixes. All that has to be done to pistons and rods is make sure the weights of all the piston and pin assemblies match, and the weights of all the rods match. For best results you would match and balance the big ends and the small ends of the rods separately.

 

I would start by balancing the pressure plate and flywheel separately, and see if it helps. I'd have the balance shop check them together before starting to see if balance is likely to solve any problems, but then balance them separately.

 

Edited January 9 by Bloo (see edit history)