Quote:
Originally Posted by wmws
Someone explain if these engines were so well balanced leaving the factory why do we now add large counter weights to smooth out vibrations.
|
In a nutshell, how the engine left the factory, ...and how many people rebuild them today are totally different. For example, when you measure the weights of today's typical replacement piston vs. the weight of an original piston, there is a huge difference. The same applies to the wrist pin. Matter of fact, today's typical replacement wrist pin is nearly 100 grams heavier than original pins.
Next consider how the connecting rods are rebuilt today. Most rebuilders add WAY more shims between the cap & the rod (-over what Ford originally did) in an effort to make the engine owner feel like he has much greater service life. Next, factor in the crankshaft pin journal is smaller, and something must take up that difference between the cap/rod and the pin journal. That 'something' is babbitt which is heavy by comparison.
The 3rd thing is most Model-A engine rebuilders are selling on a price point (--because that is what their customer wants them to do!!) and there is typically not money budgeted in the rebuild cost to do an accurate balance job. By percentages, there is only a small amount of A engines out there that have an aftermarket counterweighted crankshaft. General logic will be that if an owner is paying for the C/W crankshaft, then in all likelihood they are paying for a quality balance job too. This as a combination makes one engine much superior to the other type of 'budget-built Model-A engine'.
Does this answer your question??