I'd like to understand the difference and really understand what balancing means when it comes to the crankshaft, pistons, rods, flywheel, etc. I get balancing one thing (e.g. when something is round like a wheel or a flywheel, that's a simple concept)

I'm really not sure how to ask this question, but it's bothered me for a while. If I have to pick up a book, I will, but I know there are people in here that know this stuff cold.

What I would like to understand better is the balancing of the internals of an engine. So for example, if the pistons all weigh the same, and the rods all weigh the same, then only the crankshaft gets balanced with weights? Or does everything get touched and now you have a puzzle that has to be put together exactly as it was balanced?

How do you balance something when it isn't going in a circle and is confined to it's individual bore only? Is it purely from a not letting the crankshaft move around too much?

 

Ideally, you want the lightest piston/rod package you can reliably run. This will allow a higher rpm and thus, given the proper setup, more hp. When they balance the rotating assembly, what they do is balance the counterweights on the crank to the reciprocating weight of the piston/rod combo. A balanced, smoother running engine will last longer and rev higher. When you take your parts to the machine shop, ask them to number the pieces so you can put them back in the right spot, or do it yourself before you take them. Some rod manufacturers will number them for you. Whatever it takes to get the parts in the right place is what counts.

Hope this helps

 

Both the same thing but done different.
Internal they add/remove weight from the crank with the flywheel and balancer at "0" balance.
External is putting the weight on the balancer and flywheel.
Your LT1 is half/half-- "0" internal in the front with a "0" balanced dampener and external balance in the rear with a weight on the flywheel.

The crank is rotational weight and the pistons and rods are reciprocating weight.

The rods and pistons and rings and bearings are all supposed to be the same and the crank is balanced to that weight.

 

To add to the above : both ends of the rods are balanced independently. The rods are hung on a fixture from the small end and the big end is weighed. The big ends are then matched to the lightest rods. The rods are then weighed as a whole and the small ends are lightened to match the lightest rods. Ending up with a set of match balanced rods.

An allowance is also added for oil accumulation on the assembly, though this is just a WAG of course (wild *** guess) as the amount of oil that accumulates is obviously not an absolute.

After the parts are weighed the machinist will tally up the weights and factor what is know as bobweight. This weight is clamped to each rod journal and the crank is spun on a balancing machine that measures inbalance on both ends of the crank. The crank is then either milled/drilled to lighten or welded/drilled for depleted uraniuim or tungsten to add weight at the appropriate spot.

Idealy you should do all of your balance adjustments to the crank. The reason is if for some reason you need to change flywheels or balancer your engine won't be out of balance after the part swap. If your balancer and/or flywheel have a built in imbalance the shop can make sure that it is within spec. Same goes for neutral balance accessories.

Technically all Chevy V-8's are external balance at the flywheel regardless of rear seal type. Two piece rear main cranks have differing flywheel mounting flanges depending on the stroke. The 283 has a perfectly round flange, the 302 has a half moon cut out of one area and longer stroke cranks have a more pronounced eccentric design with the 400 adding weight to the flywheel as well. I cannot speak for the 262, 265 or 267 as I've never paid attention.
The one-piece seal crank cannot incorporate this eccentric flange and requires the weight on the flywheel to compensate.

 

Let's add on a little more....

For the longest life & best performance, especially with longer strokes a internal balance will be best. That will reduce the torsional twisting of the crank and reduce the angular inertia of the crank. That helps the acceleration of the car greatly. I do whatever it takes to internally balance a crank.

Bret

 

Man, I would really like to be able to say that I have depleted uranium in my crankshaft, but I'm afraid it's probably just boring old Mallory 3000 with tungsten.

 

Forget uranium in the crank, I'm trying to get a few gallons of deuterium for my radiator

 

Get me some too.

 

So is it possible to balance an engine well enough without the use of a balancer on the front?

And deuterium does exist naturally, so in theory all you have to do is filter/seperate the heavier water from the normal stuff. Perhaps a filtering, multi-level centrifuge setup? Might cost more than buying the stuff from a crooked nuclear engineer.

 

Yes but the "balancer" as you call it does other things beside balance.
It also absorbs vibrations that the rotating assy produce.
Ya don't want to run without it....

 

While we are on cranks and balancing...what is the proper way to store one? On its end, or side? I have one in my closet I forgot about and it is propped up at an angle! I bet it's warped all to hell.

 

maybe not.
Modern cranks are better than the ones that were used in the '40's.
I DO stand mine on end though, another old habit.

 

read this

http://www.babcox.com/editorial/ar/eb10330.htm

 

Nice!

 

A crankshaft that's internally balanced or externally balanced has nothing to do with the balance weight of the con rods, pistons etc.

The majority of the SBC engines except for the 400 are internally balanced. When they designed the 400, the increased stroke prevented them from having enough mass on the counterweights to balance the crank internally so it was externally balanced.

The BBC 396 and 427 are internally balanced and when they produced the 454, they had the same problem with not enough room inside the block for the extra weight so it was externally balanced.

Since those early days, aftermarket cranks have overcome the problems and have added an extra counterweight to make internally balanced cranks for the 400 SBC and 454+ BBC.

Having your rotating assembly balanced is something entirely different. While the crankshaft may be perfectly balanced either internally or externally, there's no way to get it perfect because of all the different weights available from different components attached to it.

Normally, with heavy pistons and rods, weight is removed from the crankshaft counterweights to neutralize the balance. However in a high reving engine like a race engine, you want lightweight components to reduce the mass that's moving up and down inside the cylinders. When this kind of rotating assembly is balanced, they add a heavy mallory weight into the crankshaft counterweights to bring it back into a neutral balance.

When an angine is balanced, the machine shop needs to know the total weight that's on each crank throw. They will bring the weight of all the pistons and pins to the same weight and each cod rod will be brought to the same weight by adjusting the weight on both ends of the rod. They'll weigh the rod bearings, bolts and piston rings. Once the total weight is known, they'll then spin up the crank with the appropriate weight on the throws and measure the imbalance. If the engine is externally balanced, the machine shop will also need the vibration dampener and the flywheel/flexplate.

The last time my engine was balanced, the crank was spun up 8 times before the balance was perfect. I have an aftermarket 4340 internally balanced crank for my 540. Because of the extra counterweight and my lightweight pistons and rods, it wasn't as easy to have the mallory metal installed but it was still done.

For most street replacement engines, balancing isn't really required. A factory engine, although close, is not very balanced because of the variation of weights between the parts. Street engines also rarely go above 5000 rpm where an imbalance vibration would be noticed.

If you start mix and matching parts with lightweight pistons or longer rods, you're really throwing off the balance weights and should have everything balanced before the engine is assembled.

Other than that, there's no real advantage to having an internally or externally balanced crankshaft. If you look at my engine and see a neutrally balanced vibration dampener on the front of it, you may think it's a 396 or a 427 but wouldn't expect it to be a 540.