Stock Rebuild........Balance question

[jdpolzin]

I'm puting together a spare motor becuase I have the parts to do so. No real use for it at this time but I'm sure I'll find one eventually. I have fresh .040 bore block, a very nice stock crank, and a set of .040 pistons already on the rods and ready to go. I know the factory didnt balance our motors and I also know that it is best to go ahead and balance to 36% for a street motor. I would rather not spend the money on this particular motor to have it balanced. I weighed the stock pistons and rods and weighed the .040 pistons and rods. Here's my results:

Stock pistons and rods: 1538g

.040 pistons and rods: 1488g



What do you think? Pretty close?

 

[thadeal4real]

your lighter as long as its the same crank your fine

 

[pick1313]

Balancing a street engine is a tricky question depending on who you ask. I think that at the very minimum you should match all the rods, pistons, pins, and bearings. You can easily do this yourself by removing minimal material and using some good scales. However, a true balanced rotating assembly requires much more expertise as you already know.

I've ran balanced and unbalanced motors(still weight matched) and could only tell noticable differences at extreme rpms. The balanced motor would rev a little quicker, not really smoother. If you were building a stroker, I'd say it's a must. Just an extra motor though................not sure.

Here's a link to a good article outlining some things you can do yourself at home and explaining bob weight, etc. pretty well

Engine Balancing - Tech - How To - Terminology - Circle Track Magazine

 

[jdpolzin]

This is actually a Remanufactured engine that has less than 3 minutes of run time. All of the weights on the rods and pistons are identical to the gram. The problem was that they put the #5 rod in backwards. The motor was pulled immediately and I bought it thinkin it would have a turbo crank as well and should be an easy fix. Well i was wrong, they used a 20/20 NA crank. So, I have a good spare crank that can easily be pollished and re-installed. I've built quite a few motors now. Some balanced, some not. I've heard people say it's a must and I've heard people say you'll be fine without it.

There's always a debate when building anything. It's obvious that it would be best to balance. It would also be best if I put 4 billet main caps, a girdle, and filled it with hard block. Those things arent going to happen. This motor is going together with parts I have had here for a while and need to put them to good use. I'm really just curious where the exceptable point is.

 

[BlownV6]

I would assemble it as is!! You will not be able to tell the difference. It will just change the rpm that it is most happy at , At 36% its most happy around an idle rpm , thats because GM need their buyers to happy while sitting at a traffic light and no vibration from the motor. A high rpm motor needs to be happy at high rpm and thus the percentage number used is usually 47 to 50%
Thats my 2 cents!! Mike

 

[jdpolzin]

I would assemble it as is!! You will not be able to tell the difference. It will just change the rpm that it is most happy at , At 36% its most happy around an idle rpm , thats because GM need their buyers to happy while sitting at a traffic light and no vibration from the motor. A high rpm motor needs to be happy at high rpm and thus the percentage number used is usually 47 to 50%
Thats my 2 cents!! Mike

Thanks Mike! Thats the verification I needed. Do you remember what we balanced my Stage motor to? I'm thinking we went to 50% didnt we?

 

[BlownV6]

I believe it is at 47% Mike