went to a machine shop to balance crank. The guy said he would have to use "bob weights." what are they and is this an expensive deal?
That must have been a machinist used to V type engines. When balancing a V8 you need bob weights to simulate the weight of a certain percentage of the pistons and rods, but that shouldn't be necessary when balancing a 4 cyl engine.
Roger, yes, he is a modern engine guy. I ask him to balance the crank. He did say bob weights and that I needed to bring him a piston/ring/rod setup. So do I need to tell him rather than this bob weight stuff, to shave material off? Or maybe I need to find another shop. One that is run by an old timer? I want to do this right.
If you have a regular T crank without counterweights, then there's absolutely no use with the bob weights, talk him out of that or use another shop.
Though I'm no authority on the subject, just repeating what I have been told by people I respect. Here's an old discussion on counterbalanced cranks where Les told us he doesn't use bob weights when balancing - and his engines are fast
Maybe ask him about a Hen weigh. If he ask you what's a Hen weigh, tell him about 2 1/2 pounds. Go to another shop. LOL
A 4 cylinder 180 degree crank shaft does not require bob weights for balancing. Find a shop that knows what they are doing. If you don't plan on balancing your rods and pistons, don't bother with having the crank balanced.
New aluminium pistons are usually very good in balance - all four within a few grams. Original rods is a completely different story - the more to choose from the better, some sets can't be balanced with just grinding, the heavy ones would have had to be ground until their strength was compromised.
Tyrone, if you can't find a good shop, let me know. Dave