#TechTip: Internally Vs Externally Balanced Engines
Internally versus externally balanced engines: what’s the difference?
First, you need to understand what it means to balance an engine. What is actually being balanced is what’s called the “rotating assembly”. This mainly includes the crank, connecting rods, and pistons.
The rotating assembly:
The crankshaft of an engine has counterweights which offset the weight of the pistons and rods, allowing your engine to run smoothly. These counterweights can be drilled out or filled with slugs to lessen or increase their weight depending on what is needed.
What’s An Internally Balanced Engine?
Basically, an internally balanced engine has a rotating assembly that’s balanced with just the counterweights on the crank. It’s literally balanced inside the engine, and all of the balancing work is done to the pistons, rods, and crank.
What’s An Externally Balanced Engine?
Externally balanced engines are engines that use the harmonic balancer and flywheel/flexplate to balance (in addition to the crank counterweights). Basically, they use weighting outside the engine to create balance.
Why You Should Care:
It’s important to know if your engine is internally or externally balanced if you plan on doing anything along the lines of an engine build or anything to do with the flywheel. Not understanding that your engine is externally balanced (and letting the machinist know) can lead to an imbalance and shaky operation.
In addition, installing the flywheel in the wrong orientation on an externally balanced engine will lead to vibrations similar to a mini earthquake.
Comments
thanks for the great article.
i must let something out though, on a side note: i HATE it when there are gifs in the article, i find them so annoying when im reading, especially since you can’t stop them!
does anyone have the same issue?
I like them if they are useful for explaining things, like the one with the pistons and crank for example.
I don’t like them when they don’t add to the article like the “the more you know” gif.
Actually seeing something move or being simulated helps a lot with understanding the subject.
One (or at least I) can stop them by clicking onto them.
That’s for cell phones though, don’t know about PC.
The GIF trend (90% GIFs, 10% content) has to stop.
The fact that you have to click on mobile for them to play is even more annoying
That’s why Roadkill’s Rotsun V6 shaked like a mother….
Yes lol they didn’t even try with it though
well another thing is the GM 4.3 V6 is a 90 degree V6 which is odd firing , it’s basically a 350 Chevy with 2 cylinders chopped off that’s why it shakes like an earthquake
But it also depends on what angle the V6 is designed at. Most modern day V6’s are set at an angle where it’s going to be balanced, but also takes up a ton of engine space because it’s essentially trying to be a boxer 6.
The Gif trend i dis/like, i like them when they are relevant and funny meme’s
The middle two suck.
Or you could have a boxer which doesn’t need balancing
You still need to balance and match the weight of the pistons, although they are inherently well balanced!
“In addition, installing the flywheel in the wrong orientation on an externally balanced engine will lead to vibrations similar to a mini earthquake.”
I do not know of a SINGLE make that doesn’ use a keyway/pin to phase/time the Flywheel so you dont induce incorrect harmonics.
Why is a balance shaft not mentioned?
So, lets say that I buy a lighter flywheel to my stock engine. Is that going to “unbalance” my engine? And those vibrations, will they occur only when you are starting to move your wheels? (I don’t know how do you call it in english when you are in a stop-and-go traffic as you release the clutch while pressing the accelerator pedal), or also while already with the shift engaged, or both? I don’t know if I’m making any sense, but I actually got curious, since that already happened to me
What engine are we talking about?
Hmm this article is a little weak. Talk about primary and secondary balance? Perhaps the physics that go into actually balancing an engine. Not just whether or not the engine is balanced internally and externally. Most engines will try to be balanced internally with the aid of external balance.