Ok,What type of fly wheel and harmonic balancer do I use in the 383 stroker????? I AM GOING TO INTERNAL BALANCE.

BUT I may not have the money to do so, so what are my options either way.

I heard that IF the motor is internaly balanced, I am to us a 350 balancer with a 350 fly wheel, or a 400 balancer WITHOUT the counterwieght in it with th e 350 flywheel.

BUT if its externaly balanced, it should be the 400 balancer (with the counter wieght in it) and the 400 fly wheel, or 400 balancer with a adapter on a 350 fly wheel. WHAT DO I USE?

Last one, What if I go manul tranny??

Its a 383 1 piece rear main seal. I have the crank and block only.

 

if it's internal balanced you'd want a neutral balanced dampner and flywheel, like from a 350, or nothing from a 400. think the crank would cost the same either way and reguardless of internal or external balance you still need to get the parts balanced.

 

Besides. If you use a 1 pc rear main seal crank it needs to be externally balanced anyway. That's just the way they're designed.

 

one piece rear seal cranks aren't externally balanced, but you'll see a lot listed in atalogs that way becasue people don't know any better. the mass of the counter weights equalls the mass of the rod piston, making it internally balanced. what the round fly wheel flange does require is a bat wing weight on the fly wheel to equall the mass differance between it and the old style 2 piece seal fly wheel flanges. from the

 

Yes. You're right. A weight that's used to balance the bob weight that's outside the engine isn't externally balanced.

It's internally balanced with an external weight. That's totally different.

Oh. What about the divits drilled out the back of the damper? Since weight was removed from that area, I guess you'd call it un-externally balanced?

 

Actually, that's exactly correct....

FOr an ideal balance situation, you want the counterweight to be exactly opposite the weight you're trying to balance. In the case of a crank, that means you'd want each balance weight to be exactly opposite the rod journal that it's counterbalancing, and you'd want 4 such weights; one for each crank throw. Clearly impossible, since the rod has to pass through the space exactly opposite it. The best you can do, is to split the required counterweight in half, and put half of it on each side of the rod journal throw. But... think about the rear-most throw for a minute. That means, you want half of its counterweight in front of the #4 throw (#7 & #8 rods), i.e. between the #6 rod and the #7 rod; and half behind it. Behind it???? Where's that? In the case of a 2-piece RMS crank other than a 400, it's the funky-shaped blob on the flywheel flange. But a 1-piece flange doesn't allow that to be there, since the seal has to slip on over it; so the other half of the "internal" weight, which happens to be outside the seal, must go on the flywheel. And once that small weight is there, now each journal has the correct counterweight equally split on each side of it, and the most nearly ideal balance situation is acheived.

If you look at any "externally balanced" 400 crank, what you'll see, is that the bottom of the piston comes too close to the crank when it's at BDC, to allow a sufficiently-sized counterweight to fit on the crank. The counterweight can't be perfectly circular in circumference, like an internally balanced crank; instead, it has a flatter portion cut off of the CW circumference, to clear the bottom of the piston at BDC. Then, whatever left-over weight that couldn't be placed equally on each side of the rod journal throw, has to be located externally instead. When that happens, the counterweight is no longer located directly opposite the rod journals, and the crank is no longer dynamically balanced, even if it's statically balanced (i.e., such that if suspended in space, it won't try to rotate a heavier spot to the bottom). Instead, there will always be some amount of rotational moment left over, tending to make the crank want to rotate around an axis perpendicular to the main bearings. It may be relatively slight, and it may be possible to cover it up by damping it or whatever; but it's still there, inside the metal of the crank even if you can't feel it. It's what breaks cranks at high RPMs.

The 2 center rod journal throws of a 400 crank (#3 & #4, and #5 & #6) are located perpendicular to each other, thereby counterbalancing each other partially. They do so enough that it's possible to fit enough counterweight in the remaining available volume, for those 2 throws to dynamically balance. The front throw and the rear throw are the problem spots, since they have no other rod throw perpendicular to them right next to them; they require their entire CW to be next to them. Those are the 2 that don't fit, and require a part of their CW to be located on the balancer and on the flywheel.

 

I fully understand what you're saying, but I just don't see the "harm" in calling it externally balanced since part of the weight, however minute, is "outside" the engine.

I see your point though. Based on what I'm saying and what you explained, all SBC's are "externally" balanced since that rear portion of the crank has offset weight. But IMO, if it isn't "part of" the crank (i.e. it's attached later on) then it's considered externally balanced.

Without trying to sound prude, perhaps if there was a way to correct the late John Lingenfelter you'd need to. It does say in his book (including other books of other authors) that the 1 pc rear main seal blocks are considered to be externally balanced.

It's not just some term "people that don't know any better" just made up.

Oh well. The point is moot. Even if it's not a "technically correct" term, it's still the way it's understood and the term used to communicate the meaning of the way the balancing is done on that type of crank. So as long as "people that don't know any better" all use it, as well as those who do "know any better", then no confusion exists.

 

No.

If it's possible to put exactly half of the the required counterweight on each side of the front and rear rod journal throws, it's internally balanced. Period. Even if part of that "internal" weight actually appears on the "outside" side of the oil seals, or even if it's part of some other physical piece, such as the bat-wing weight on the 1-pc RMS flywheels. Even though that weight "looks" suspiciously like it's "external" to the motor, the crank itself is still "internally" balanced.

Look at the front of the motor for the actual indicator. Notice that the entire required counterweight for the front rod journal throw, is able to fit between the bottom of the piston at TDC and the crank centerline.

Sometimes, one's "opinion" doesn't count for much, in comparison with the terminology used as the "industry standard". Some things aren't worth arguing about. Some things aren't subject to "opinion".

 

Whuch do I use??? 350 flywheel and balancer or 400 flywheel and balancer? Can a machine shop internal balance or not?



Building a 383 stroker.

 

That's not what I meant.

Oh well. Once again RB reads what he wants to.

 

If its internally balanced, use a 305/350 flywheel.

 

The machine shop can internally balance your 383, if 3 things are true:

1) Your crank has counterweights that aren't "flat cut" for use with the short 400 rods (see definition of "internal" and "external" balance above); and

2) You use rods that are long enough to fit with circular counterweights; and

3) Your rod & piston bob weights are within the range that the crank counterweights can be trimmed to.

If all 3 of those are true, then it is possible to internally balance your crank, without the use of Mallory metal. If they are not true, you can probably still internally balance it, but it will cost you as much to do that, as buying an internally balanced crank.

Note that I said "it is possible"; not, "it's internally balanced". You still have to depend on your shop for accurate and informed information about what you've got and what they can do with it.

If the shop can internally balance it, then you'd use a 305/350 balancer and flywheel.

If the shop cannot internally balance it, you'll have to use a 400 balancer & flywheel.

Beyond that, you're kind of on your own.

I can only read what's written. I'm sorry if what what's written says, isn't what you mean to say. "Internal balance" means a specific thing that's well understood industry-wide, and "external balance" also has a specific pre-defined meaning. It's not subject to interpretation or opinion. And it doesn't really mean solely that the weight is inside the oil seal.

 

I guess this is where the confusion is, so I'll ask...

If a 400 crank is "externally balanced" and has a weight added to the harmonic damper and to the flywheel/flexplate, and a 1 pc rear main seal crank has weight added to the flywheel/flexplate, yet removed from the damper, why wouldn't it be called "externally balanced"?

That's what I'm saying most people's thinking is, as well as mine, perhaps do to not having experience balancing an engine.

Let me also ask you this, and maybe it'll clarify my thinking...
Can a 1 pc rear main seal crankshaft be balanced without the use of a flywheel/flexplate with the weight added and/or the damper with the damper with the weight removed?

Yes, I know those things are supposed to be neutral balanced (i.e. no weight added nor removed from them) so they can be easily replaced without the entire assembly needed to be balanced again, but can you balance that style crankshaft without them?

From what I have understood in the past (as well as Mr. Lingenfelter) that's what seperates an internally balanced engine from an externally balanced one. Evidently not?

 

It costed me 350 bucks to balance it with mallory metal. NOT cheap

 

Consider the simplest possible crankshaft. It would be a straight shaft, with one rod journal; it would have a main bearing at each end; it would be no longer than it had to be to accommodate the rod journal. This would probably vibe severely in operation, no?

Now consider what you would do to balance it. The simplest thing you would do, would be to make the shaft a little longer at one end, and add a balance weight on it next to the journal. Better; it would probably run OK at relatively low speeds, but once you get it going pretty fast, you'd see one end try to go flying off one way, and the other end trying to go flying off the other way; and it would still vibe.

Now, let's take that balance weight, and cut it in half, and put the halves on either side of the rod journal. Now we've got something that will run smooth; because the point along the crankshaft's length at which the rod journal's moment of inertia acts on the crank, is the same point at which the sum of the balance weight halves act on the crank.

OK; now imagine that we have 2 rod journals, next to each other along the shaft, and directly opposite each other. Obviously, the crank is in "static" balance without doing anything at all. But, we've got the same issue as before, with one journal and one counterweight; it's going to vibe like hell. So, we still need 2 counterweights in this configuration, one at each end of the crank. They would need to be sized such that the sum of the rod journal on one side and the weight on the same side but the other end, acted on the crankshaft at the same location as the other journal/weight pair ("moment pair").

Keep in mind, that from both a manufacturing cost and a long-term longevity standpoint, we'd want the weights to be the same piece of material as the crankshaft itself. We wouldn't want any possibility of them coming loose, and we wouldn't want to have to use sections of metal of different weights to arrive at the ideal confguration. That puts some practical limits on how heavy the weights can be, because they're made out of the same density material as what they're counterbalancing.

Now, let's skip some imtermediate steps of increasing complexity in the thought experiment; and imagine that you have multiple rod journals, and that the pistons on your crankshaft form a pretty much uninterrupted mass from end to end (that being the point of an engine....). But, because the rods are short, the pistons in this situation, come so close to the crank centerline when they're at BDC that it's not possible to locate the weights such that all weight/journal "moment pairs" act at the same point on the crank. In a V8 motor, it's nearly always possible to locate the center ones so that they do, because each journal partially counterbalances it neighbor; but the end ones, are a problem. There's not enough room along the length of the shaft to locate enough weight at the ends at the ideal location for the weight. That's what's meant by "external balance"; not, just that the balance weight happens to be located beyond the oil seals. It means that there has to be extra weight located "externally" beyond the correct location for the optimum "moment pair" to be created, and that the optimum static balance (low-speed vibration) and dynamic balance (high-speed vibration) cannot be achieved simultaneously.

It's not a matter of "most people's thinking". It's a matter of physics, and numbers, and hard reality, and applies to alot of things in the world at large besides SBC motors.