Got a 71 350, swapping in a crank from another 71 350. Any issues balance wise? I doubt the cranks were matched to the rods.
Cranks from every year can be slightly different. Visually measure / look to find any small changes. If going 71 to 71, you should be real close and can replace the slugs in the harmonic balancer exactly the way they are now. Flex plate should work also, unless there are balance clips on it, then swap those over too or remove them if new crank flex plate didn't have them. Read up on balancing in the service manual...
All I have from the other motor is the crank. My current one is scored enough to need machined but it being so close to thanksgiving I'm kind of on a time crunch.
Should be just fine. The factory didn't balance each engine separately, they tried to make the parts weigh all the same so they could assemble 500 engines per shift.
You don’t have much to loose, try it. The engine was likely barely balanced by the factory. All they did was stick a few weights in the balancer to reduce vibrations. It’s not like they actually cared to spend any time balancing the engine it was a hack job good for 3500 rpm
But at the same time balancing could be why my motor has lasted over 25 years banging at 6 grand all the time.
This is a good point. I do a proper internal balance on my engines but it’s only worth it if you are using high end parts. For a stock rebuild it’s likely good enough.
After comparing cranks, it's a no-go. Using the original it is. Should clean up with .010/.010. Casting numbers were the same, visually the same except the holes. Ah well. I suppose it's for the better.
Buick had the goofiest balance system in the industry, at least for domestic producers. Nevertheless, they balanced every individual engine using the slugs in the damper and offset weight on the flywheel/flexplate. I'm not saying they did it with accuracy. But they did "balance" individual engines.
If both engines were stock swap the crank and be done with it. It may look different but it will be close enough. Crank kits and other crank swaps have been normal in any engine rebuild with no issues. These engines were NOT individually balanced from GM. 99% of the factory balance came when the engineer drew the crankshaft and figured how heavy the counterweights needed to be.
I dropped the crank off at the shop, so no pics, but the front most crank throw's hole was about .630 in diameter (digital calipers), and shallower than my other crank which had a .867 diameter hole and was at least an 1/8 deeper.
You can always mess with it by putting lead fishing line sinkers in the holes of the balancer and seeing what it does. Just pick a hole, put the weight in it, then rev the engine up and see if it's any smoother or rougher. Move the weight around. If it ran smoothest with no weight, then it's in pretty good balance.
