Re: engine balance

Posted by Tim Cole On 2015/10/24 16:48:08

I think this thread is going overboard. Imbalance in an under square long stroke motor like a Packard is going to have a magnified effect if the replacement parts do not weigh the same as the original parts.

If NOS Packard parts were being used to overhaul an engine then rebalancing would be a waste of time. Once I compared the weights of an original '33 Super 8 piston to a popular cast replacement brand and they were nearly identical.

However, on that motor job the original rods were welded, rebored, machined with an iron thrust surface,and fitted with rod bearings from a Chrysler 360 V-8 or something.

So who wants to guarantee that job without a rebalancing?

There is more to balancing than the crank. The counterweights have to be adjusted to match the reciprocating weights. So if you bore a cylinder the reciprocating weight will change and require a rebalancing.

There is motor overhaul and there is motor rebuilding. The two are not the same. Dealers overhaul motors. They do not rebuild them. An overhaul is a repair not a rebuild.

Next issue is align boring main bearing caps. This process involves milling the caps and then resizing them to correct out of round conditions. If you are overhauling a motor you don't bother with this.

Finally, I don't think any of this modern super computerized machinery is doing a better job of balancing than the Packard company did. For one thing these machine shops are still under the shade tree, whereas the Packard company was a manufacturing plant. Just because a torque wrench has buttons on it doesn't mean it is going to be more uniform than a good old fashioned Sturtevant heavy beam torque wrench. To say otherwise is like saying that computers improve arithmetic.