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Stallion
12-08-02, 10:30 PM
I'm pretty sure I understand the functionality of the crankshaft and how that works and all. I was just reading Newton's comments about the balancing of the crankshaft, and I wasn't sure that I totally understood what he meant.

I think he was saying that some blocks are balanced internally, while others not?? I'm not sure. Can somebody explain the balancing of the crankshaft?

Thanks! :D

TR

Eric
12-08-02, 10:40 PM
Again I turn to the trusty Corvette Glossary (http://www.corvetteactioncenter.com/forums/glossary.php?s=&ltr=B) for a pretty good explanation.


Balance a Motor/Crank
Balancing is to grind or add metal to the moving parts so that the assembly is balanced and runs smoother. Basically each piston, pin, rings, and rod are balanced so each weighs the same as the others. Then the crankshaft is set so the weight of each piston/rod assembly matches the counterweights on the crankshaft. The factory balances within an allowable tolerance but for special performance, racing, or just ultimate smoothness, you need to have the assemblies balanced further. It is not something you need to take an engine just out to have done, but if the engine is being rebuilt or is having other major work done, then you should balance it. Flywheels and the clutch pressure plate should also be balanced, as should driveshafts.

When the time finally comes for you to buy a Vette, you are gonna have more knowledge than any of us;).

Stallion
12-08-02, 10:46 PM
Okay, I think I understand what is meant by balancing the crankshaft. But, say the crankshaft wasn't perfectly balanced. What would be the problems arrising? Logically, would the crank have uneven revolutions, maybe? I guess a "bouncy" turn? What?

Thanks, Eric! And, again, I promise that before I post I will look in the glossary. :( Sorry... :)

TR

Eric
12-08-02, 10:56 PM
Hehehe, here's another term for you - Harmonic Balancer. Since very few cars actually are balanced and blueprinted, the Harmonic Balancer has the job of keeping everything in "harmony" and not spinning out of control.
- Eric:w

Stallion
12-08-02, 10:59 PM
Eric, I think I know what you're referring to, but I'm not sure. Let me try to explain what I think you are referring to on the engine...

I was this one picture of an engine (out of the car, hanging from a crane/lift) and on the front of it (like you said) was a big fan-looking part. I didn't know what this was, and I figured that it was just a means of cooling the engine, but now that you bring up the HB, you make me think again. I don't know if I explained it well, but is this part I'm thinking of the harmonic balancer?

Thanks! :D

TR

vigman
12-08-02, 11:47 PM
From the GM factory the engine's rotating parts are balanced to what GM considers OK....
BUT
In a perfect world and you could suspend the crank on bearings that had 0 friction and spin the factory crank in a test jig

It would stop at the same place everytime since the weight was not equal of all the journals. ( see gravity does work)

So you would now take a little metal off each journal so the crank would not stop at the same place twice... or more even displacement of the weight.

Internal vs external

the difference is.... the internal is the crank itself.. with no flywheel.. or harmonic balancer.

And external balanced crank NEEDS the weight of the harmonic to be a completely balanced assembly.

But there is more to the puzzle.. the weight of the connecting rods, pistons, wrist pins, bolts.... ALL affect this equasion.

You could have a perfectly balanced crank and 2 pistons that were 4 grams heavier than the rest.... not balanced!!!!

If this engine was in Grandmas market-mobile.. no problem.

running at the Winston 500... BOOM!

If you want to see some pictures... check out my Mystery 327 & mystery327 next generation posts.



Vig!

Stallion
12-09-02, 06:59 AM
Okay, I think I understand. So, there are two types of cranks, internal and external? I think I see now. So, we just have to make all balanced. Okay, thanks! :D

TR

JohnZ
12-10-02, 02:47 PM
Just to amplify things a bit more:

On an internally-balanced engine (which most Chevys are, except for the 400SB, 454BB and post-'85 350's), the harmonic balancer name isn't really correct - GM calls it a harmonic damper, as it has nothing to do with engine balance; it's neutral-balanced, and is there solely to absorb and damp out dynamic torsional vibrations in the crankshaft which could otherwise cause a fatigue fracture.

The externally-balanced engines use a different version of the harmonic damper which also incorporates an offset weight in the outer ring, which works in harmony with an offset weight on the flywheel or flexplate at the rear of the crankshaft to achieve proper engine balance (post-'85 350's only have an offset weight on the flywheel/flexplate and use a normal harmonic damper).

The externally-balanced engines are that way because there isn't enough room inside the crankcase for crankshaft counterweights large enough to offset the effects of the reciprocating components; thus the need for additional external weighting to achieve proper balance. :Steer

Eric
12-10-02, 04:20 PM
As always, very informative John! :upthumbs

- Eric:w

Stallion
12-10-02, 07:52 PM
Originally posted by JohnZ
Just to amplify things a bit more:

On an internally-balanced engine (which most Chevys are, except for the 400SB, 454BB and post-'85 350's), the harmonic balancer name isn't really correct - GM calls it a harmonic damper, as it has nothing to do with engine balance; it's neutral-balanced, and is there solely to absorb and damp out dynamic torsional vibrations in the crankshaft which could otherwise cause a fatigue fracture.

The externally-balanced engines use a different version of the harmonic damper which also incorporates an offset weight in the outer ring, which works in harmony with an offset weight on the flywheel or flexplate at the rear of the crankshaft to achieve proper engine balance (post-'85 350's only have an offset weight on the flywheel/flexplate and use a normal harmonic damper).

The externally-balanced engines are that way because there isn't enough room inside the crankcase for crankshaft counterweights large enough to offset the effects of the reciprocating components; thus the need for additional external weighting to achieve proper balance. :Steer

Hey, thanks for the information, John! Is the harmonic damper something that doesn't need to be maitained too often? It sounds like if it goes, there could be some big problems. Ever have to work with one and fix/change it? Or not something that goes in the Vette lifetime?

Thanks again! :D

TR :Steer

JohnZ
12-11-02, 05:04 PM
Generally, they last for many years and don't require any maintenance - eventually the rubber isolator between the inner hub and the outer ring will deteriorate, but it's easy to see when that starts happening. Replacing them requires a removal and installation tool (to do it right), but it's usually only necessary when the engine is out of the car for teardown/rebuild or replacement of the timing set.

Stallion
12-11-02, 05:19 PM
John, it's funny you should mention timing. I still am a little foggy on the timing of an engine. I mean, I know how most of it works and how everything works together with the timing and all and the strokes.

But what I'm not sure about is what happens to timing when you modify parts of the engine. For instance, if you put in a new cam with a higher lift and less duration for more power, then what would that do to the timing of the engine and strokes? Would you have to do anything to compensate for that sort of thing?

Thanks again! :D

TR

sscam69
12-12-02, 04:31 AM
Apparently not

John explained this on another thread I started.

It was titled "Timing what the engine wants or what I want"

John wrote a good explanation of what you should be shooting for and why when it comes to proper engine timing and I posed the same question you did. There were other sources for this information posted on that thread as well.

Do a search and you'll find it.

Frank

sscam69
12-12-02, 04:45 AM
I guess I am curious about a few things as well when it comes to balancing.


When it comes to high performance engines which would be the better option. Internally vs Externally?

Lets say your running 600+hp/600ftlbs and spinning the engine up to 6.5krpm-7krpm on a blown app. with lightweight pistons. Lets say with an L/A ratio of about 1.7.

Which would benefit you more for engine longevity?

When it comes to the balancing act how is the crank balanced? What I mean is the counterweight mass is set but as the rotating assembly accelerates the forces generated become amplified. In a perfect world the mass of the counterweights would increase to compensate for the amount "pull" the piston is doing on the exhaust stroke.

I guess what I am getting at is at what rpm should the crank be balanced for the above mentioned app.? 3k.....4k.....6k rpm and how much is an "acceptable" imbalance 5g....10g...20g?

I don't know if what I am writting makes sense, if it is confusing I will try and rephrase my questions.

Stallion
12-12-02, 07:02 AM
sscam69, I don't know if we're referring to the same timing (if there are even two timings in an engine). Yours seems to be about ignition, but I'm talking about the overall synchronozation (sp?) are the engine if you would do such a mod.

And, when you talk about the degress of turning something, sscam69, what are you referring to? I saw that you were experimenting with the idle and these degress. Can you try to explain this concept a little better to me?

Thanks! :D

TR :Steer

Stallion
12-12-02, 07:09 AM
Now that I think about it, I guess ignition is a big part in timing and the spark plug and all. Because, for the combustion of course the spark plug is needed and if that is off, I don't know. Explanations? :)

Thanks! :D

TR

Stallion
12-13-02, 11:15 AM
Timing...anybody?

Thanks! :)

TR

JohnZ
12-13-02, 08:05 PM
Two kinds of "timing" - cam and spark (ignition). Cam timing refers to how the cam profile sets the opening and closing of the intake and exhaust valves relative to the position of the piston at top and bottom dead center, expressed in crankshaft degrees; these events are fixed and are constant relative to the crankshaft, which drives the camshaft through the timing chain (some modern overhead-cam engines have variable cam timing, with an advance/retard mechanism between the front of the cam and the sprocket that drives it).

Ignition timing is the point where the spark plug fires relative to the position of the piston on the compression stroke, expressed in degrees of crankshaft rotation ahead of top dead center. Do a search on my other post referenced above for an explanation of why it's necessary to vary the amount of spark advance depending on operating conditions, and how it's done.

Engine balancing question - first, each cylinder's reciprocating mass package (rod and bolts, bearings, piston and pin and rings) is weighed and matched to within 1/2-gram of each other by grinding the seven heavier ones to match the lightest one; then a "bob-weight" is made up for each rod journal on the crank from a calculation based on two cylinders' mass package, and the crank (with the bob-weights attached, and the harmonic damper/balancer and flywheel/flexplate if the engine is externally-balanced) is spun in a balancing machine. The machine determines where on the crank that weight needs to be removed in order to achieve perfect balance, and a large drill is used to accomplish that (you can see the drill holes on the O.D. of the counterweights on a crank that's been balanced). In rare instances on some high-performance engines, to avoid using external balance weight devices, weight needs to be ADDED to the counterweights - this is done by drilling holes in the side of the counterweight cheeks and welding in slugs of "Mallory Metal", a very dense (and expensive) alloy. The Viper V-10 is one of the few production engines that requires this process, and its counterweights are also fully-machined, both on the O.D. and the sides of the cheeks (see photo below).

Viper cranks ready for installation:
http://image1.villagephotos.com/pubimage.asp?id_=349602

Viper engine on the build dolly (we build them by hand):
http://image1.villagephotos.com/pubimage.asp?id_=349603

Stallion
12-13-02, 10:45 PM
So, the crankshaft actually drives the camshaft? Is that how the cam timing always keeps fine without screwing everything up? Because, if the cam is change for, say, longer duration, the crankshaft feels the change and then it directly controls the cam so it will all work out like that? Does the crank control the cam through the pulley system?

Thanks, John! :D

BTW, is that Viper engine a V10? It looks like there are 5 cylinders from that picture on the view. Correct?

JohnZ
12-14-02, 03:25 PM
The cam is driven by a chain from the nose of the crank, at 1/2-crank speed, since the crank makes two full revolutions for a full firing cycle and the cam only makes one.

Yup, the Viper engine is an all-aluminum V-10; was 488 cubic inches through 2002, the 2003 is 505. It has more brute torque at lower rpm than any other naturally-aspirated production engine on the planet - the original "torque-monster" :D

sscam69
12-14-02, 05:28 PM
John why did Da. Ch go with a V-10 configuration as compared to a V8 configuration.?


I was reading that a V-10 config allows you to achieve "Big Block" cubes but generate less harmful emissions compared to a V-8 configuration given the same amout of cubes

JohnZ
12-15-02, 04:56 PM
The V-10 configuration allowed "big-block" cubes (for torque) with "small-block" combustion chambers; this reduces the surface-to-volume ratio in the chamber, which allows for more complete combustion (shorter flame-front travel and reduced dead-space volume above the top ring land) and simpler emission controls.

The pulleys just drive the belt-driven accessories (water pump, alternator, power steering, A/C compressor, etc.) - the crank drives the cam with toothed sprockets and a chain (the "timing chain") so their relationship never changes; the cam sprocket has twice as many teeth as the crank sprocket so the cam turns at 1/2-crank speed.

Stallion
12-15-02, 10:20 PM
Okay, thanks, John! I understand now that the timing is calibrated with the cam modding and sorts. Thanks again! :D