irocbrninrubber

I am rebuilding my 350 .030 over, i am going to use holley systemax II aluminum heads, cc276hr and hyper pistons. A few friends have told me to balance the rotating assy, but the machinist told me that with the amount of power i will be making that it should not be an issue. I am thinking i will be around 420 fhp. what do you guys recommend? Thanks in advance.

igotta355z28

iTrader: (1)

dont worry about it check out this thread https://www.thirdgen.org/forums/tech...html?highlight=

Supervisor42

Didja ever take apart a stock engine?
Didja ever notice the connecting rods are numbered?
I wonder why that is?
Here's some news: The vast majority of engines that are running out there are balanced.
If you believe that "just keep it below 5500" crap, just ask yourself why the factory wastes time and money on doing something if it is totally unnecessary.
Trust me. The factory don't waste a dime...

Guest

Numbered? I havent taken one apart yet that was numbered... not a SBC anyway, not since the old 327 rods laying in the shop at work have I seen them numbered or stamped.

Supervisor42

I guess I'm showing my age...

Supervisor42

Let me state it a different way. Every engine that every manufacturers builds is balanced. It costs money to do this. If they didn't have to, they would gladly pocket the money. Harmonic balancers are balanced. Flexplates are balanced. Flywheels are balanced. Clutch covers are balanced. Even driveshafts are balanced.
When you bolt together a bunch of parts that will become the heaviest rotating part of a car without balancing it, it's like dealing a 5 card hand of poker.
It can vary from extremely good to extremely bad based on nothing but luck.
Most will be in the middle: not good, but not bad.
How much are you willing to bet, and do you feel LUCKY?

AlkyIROC

Factory engines are balanced but not to a high precision of an aftermarket balance job.

You're using larger pistons and they're different weight pistons. That's changing the bob weight on the crank throws. It will be out of balance. It will still run and you may not notice anything but an engine put together with non factory parts in the rotating assembly should always be balanced for a smoother running engine and longer life before it beats the bearings out.

Guest

Balanced to some degree. Most of the SBC's I have come across are fairly close, at least the rods. The pistons arent so good. I wont get into other manufacturers... like one that had the absolute heaviest rod in the motor attached to the absolute heaviest piston... and believe me that motor ran much smoother after I fixed that.

ChrisPcamaro

Kinda dumb question... what all is included in the "rotating assembly" when you're talking about balancing it? And how do they balance it?

Guest

Depends on who you talk to. Some say they gotta have the harmonic damper/balancer and rear flexplate/flywheel, and some dont. In any case the crank, rods, and pistons need to be there. I've seen some requests of rings but I'd hate to see a set of rings off that much.

Its kind of a money thing, if you have it, you cant hurt the engine by balancing it. If you're on a budget and thats not in your budget... chances are if the rods are original and your pistons are 'matched' as they come from the aftermarket, it'll be fine for most people. Those that are pushing the limits of the parts and going past the 6k mark, might want to fit that into the budget just to eliminate a potential failure point. Make it break somewhere/somehow else

AlkyIROC

After seeing my neutrally balanced flexplate off by 10 grams, I recommend sending the flexplate/flywheel as well as the harmonic balancer even if it's an internally balanced engine. 10 grams doesn't sound like much but that becomes many pounds at 7000 rpm.

Parts required for balancing:

Flexplate/flywheel with mount bolts and dowel pin if required
Harmonic balancer
Crankshaft
Rods with bolts/nuts
Pistons
Wrist pins w/locks if required (floating pistons)
Rings (one set)
Rod bearings (one set)

InfernalVortex

iTrader: (4)

My shop asked for my crank, rods, pistons, rod bearings, and rings to balance my motor. OF course, Im running a stock stroke 350, not a 383. If you're doing a 383 I think it gets a little more complicated.

AlkyIROC

Externally balanced engines need to send in the flywheel/flexplate and balancer because there are balance weights on them that are required. Even if your engine is internally balanced, it's good to get it balanced with the flywheel/flexplate and balancer also. If the balance shop says they don't need them, find another shop. A good balance shop will know that even though they're neutrally balanced, they'll still not be perfect.

Ask them to spin up the crank with and without the flexplate and balancer to see how much difference there is before they start adjusting the weight. A few grams out can make a big difference at higher rpms.

InfernalVortex

iTrader: (4)

If the rotating assembly is neutrally balanced, then in theory all you would have to do is make sure the flexplate and balancer you bolt to it are also neutral balanced. Im not sure how you'd take weight ouf of a balancer, but I'm assuming you can, probably?

But if everything in between the flexplate and the balancer are neutral balanced, then why would you need to get a custom balanced flywheel/flexplate and balancer? I didnt want them to balance my rotating assembly to my flexplate/balancer because of various reasons. I'd rather them get the important parts neutral, and the rest of it can be balanced neutral to match later on without much trouble.

OR.... I'm missing something really obvious?

DSmith

I just had to deal with this crap. I ordered a internally balanced rotating assembly. Balanced at the factory. when I took the block to the machine shop the guy seen my crank and other part and asked if I was gonna have thme balanced. I told him I ordered a "balanced assembly." and I didn't need him to do anything. He just shock his head and said I want to show you something. He took my "balance assembly" in the shop and set everything up (this took a little while) when he was ready to turn on the machine he said that if my assembly was within 25 grams he would do my block work for free and if it was out it would cost $130 to make right. I paid extra for a "balanced assembly", I was looking forward to getting my block bored for free. 284 grams out of balance later I was pissed. He told me that a neutrally balanced crank was what I had meaning the crank by itself was neutral and that the matched set of rods and pistons only meant that the set of rods were matched and the the piston were matched. GUYS when he turned on the machine the shook. That could have been my engine. I have built several engines and ran high rpms without balancing them, some ran great, others wasn't smooth at all. My boat engine (also a 350) has a hell of a vibration to it and its NOT balanced. The engine I'm building now is a 383 and I wanted everything to be perfect so I paid extra for a balanced assembly.

Is it worth the extra money to balance an engine? Ask yourself this, what if I had NOT let him check mine? How would my 383 turning 6k or more ran being 284 grams out of balance?

If its a stock engine and your rebuilding it with stock parts you could be fine.
If it has aftermarket performance parts I don't care who made it, BALANCE IT.

Supervisor42

THAT'S what I'm talking about.
Looks like you drew a pair of deuces...
Anybody else want to play?
Has the OP left the building?

EvilCartman

iTrader: (1)

Had all of my stuff balanced, smooth as silk. The old 305 wasn't as nice and felt like it was going to fly apart at any moment.

tekkitan

iTrader: (1)

This is WONDERFUL information for beginners. I am starting on my first engine build (which is also a 383) and looking at "balanced rotating assemblies". I am sorry you had to go through this, but that story has given me insight on these balanced kits now.