Engine balance

[Dan Ward]

Hello,

Is a champion 185 engine an internally balanced engine or externally?
I'm not familiar with this terminology. It apparently has to do with whether or not they use things external to the engine to balance with. Like the flyhwheel or harmonic balancer. I'm told that if it is externally balanced they will need to balance the entire rotating assembly--flywheel and all--or maybe the torque converter if it's an automatic. This does not really make sense to me because the purpose of balancing the engine in the first place is " to get it in balance". Can anyone speak to this? Thanks Dan

[gordr]

I'm pretty certain the 185 is internally balanced. Some engines DO have flywheels and harmonic balancers with offset weights to balance an otherwise unbalanced crankshaft. One such that I know of is the Chevy 454. I knew a guy who pulled a tired 396 (internally-balanced) from his tow truck, and swapped in a 454, using the same flywheel. darn thing nearly jumped out of the frame when he fired it up. He found the proper flywheel, which was milled out on the front side, save for a bug pie-shaped sector.

I have a dead 185 in the yard, and I could pull off the flywheel and check if you wish.

Note: if you are balancing for high-performance purposes, I expect it would be wise to balance the entire rotating assembly anyway.

Gord Richmond, within Weasel range of the Alberta Badlands

[Dan Timberlake]

Are you chasing a vibration problem?


Many US V-8 engines are "externally balanced" with a precise amount of unbalance in the flywheel and damper positioned to align with the crank counterweights.

http://www.northernautoparts.com/ProductDetail.cfm?ProductId=2416

Some engines just are externally counterweighted at one.

Adding material to the crank in the form of "fish plates" or filling holes with metal denser than steel can convert an externally balanced engine to an internallly balanced engine. Some folks claim an internally balanced engine is gentler to the main bearings.

External balancing is required when the counterweights on the crank could not be made large enough, either because the engine was very compact internally (small block Ford), or the stroke had been increased over the years (400 small block Chevy), or a forged crank had been redesigned as a fatter casting (small block Dodge).

Inline 6s and 8s are "inherently" balanced, so don't really need a particular amount of crankshaft counterweight, so they always >can< be internally balanced. But not all >are< interanlly balanced. Of course at least one manufacturer has chosen to externally balance their inline 6. Mercedes 300SL comes to mind. They had a relatively small amount of counterweight/contolled unbalance in the damper and flywheel, so it was most practical to balance the crank with flywheel, etc attached. The shop I worked for worked out a system with a 300 SL specialist, where the crank was "zero" balanced, and the flywheel, etc was zero or neutral balanced to simplify future repairs, like flywheel refacing and rebalancing. In that application the components could easily be zero balanced, and the performance proved to be indistinguishable from the OEM setup.

But, if an inline 6 crank was welded, or has suffered a badly spun bearing, there can be distortion that grinding the main journals in-line does not fix. For instance, the rear main seal surface and flywheel pilot diameters and cam drive sprocket/gear journal will have runout. balancing the flywheel and clutch on the crank will compensate for flywheel pilot runout, but not the others.