Harmonic Balancer Question(s)

[Eric]

To all:

Could somebody explain to me the difference between the harmonic balancers on the Ford 5.0l and 5.8l? It is my understanding that there are three styles: 28 oz, 50 oz, and neutral. Which engine uses which balancer for which years?

While I am interested in the above information for future reference, ultimately my question is this, will a harmonic balancer from a '98 5.0l work on a '96 5.8l?

Thanks in advanced.

Eric

 

[Jeff Hamilton]

302/ 5.0 up until 1980 (dip stick in timing chain cover) is 28 oz.
302 1980 and up (dipstick in side of block) are 50 oz
All 351 /5.8 are 28oz.
The short answer is no.
Jeff Hamilton

 

[Bill Musarra]

Eric,
Of the engines that Jeff outlined, all can be internally balanced. I did my 351 Windsor and it runs very smooth. Little vibration at all. Slightest movement from the torque. My front mount incorporates the polyurethane bushes(3-4 inches long), but little movement from them at all.

Bill

 

[Eric]

Would a machine shop be able to take a balancer for a 5.0 liter (50 oz) and make it work for a 351W? What would the machine shop need to do this, just the balancer or the balancer, flywheel, and crankshaft?

Alternately, I have not gotten my flywheel yet, would it be possible to use the combination of balancer and flywheel for a 5.0 liter (50 oz) on a 351W without a trip to the machine shop?

As you may have deduced, I have a balancer from a 5.0 liter that I want to use on my 351W and am looking for a way to do so. Thanks in advanced for input.

Eric

 

[Wally]

The Machine shop could do all the components, Only they will need the complete rotating asm ( Crank , Rods , Pistons , Flywheel , and Balancer. Plus $$$ to get off the extra weight from the right locations.

 

[Howard Jones]

No, that won't work. The crankshafts themselfs are 28 or 50oz parts. You cannot mix and match 28oz parts with 50 oz parts without at the least a complete rebalanced of the complete motor. I'm not sure if they will even fit. My advice is to trade the 50oz 302 unit for a proper 28oz 351 dampener and balance the motor with your new correct 28oz flywheel.

You should be aware that using a mismatched part in the rotating assembly will more than likely result in a huge mis-balance and a resulting engine failure. This includes, dampener, dampener V-belt wheel or serpentine wheel, internal parts (pistons,rods,crank), flywheel, and clutch pressure plate.

Everything should be balanced together by a qualified machine shop that does lots of engine balance work. Find a well known shop in your area and ask your questions. He might be able to point you in the direction of a even swap for the dampener.

 

[Cliff Beer]

OK, here's a dumb questions (please delete if this is too much thread drift) - why does a SBF need a harmonic balancer? Is the stock crank not already balanced with counterweights? Is there some basic design imbalance that's different than other V8s???

Related, does an external balancer just get the thing into basic rough balance? In other words, if you want a really nicely balanced engine is there an on-the-bench balance process with the balancer in place?

 

[Eric]

Cliff

The main purpose of a harmonic balancer is to absorb tortional vibrations, or harmonics, cause by the pulses of the combustion pressure in each cylinder. All reciprocating-piston engines experience these pulses. With each combustion event, there is a momentary acceleration of the crankshaft, followed by a deceleration until the next combustion event. This "pulse" actually twists the crankshaft about its centerline, which is called a tortional vibration.

If you look closely at a harmonic balancer (now commonly called a "tortional vibration damper"), it is constructed of two heavy steel rings with rubber sandwiched in-between them. The rubber, along with the inertia of the two spinning masses, cushions, or flattens out, the tortional vibrations.

The harmonic balancer does not balance the crankshaft, as I believe you are thinking.

Eric

 

[Wally]

HI Eric The SBF is an Externally balanced engine in stock form, Requiring balance weighs on the Flywheel and Harmonic Balancer.

Internal Balance & External Balance

When the counterweights alone can be made to balance the crankshaft, the crank is said to be "internally balanced". If the counterweights are too light by themselves to balance the crankshaft and more weight is needed, an "external balance" can be used. This involves a harmonic dampener or flywheel that has a weight on it in the same position as the counterweight that effectively "adds" to the weight of the counterweight on the crankshaft.

Since the harmonic dampener (front) or flywheel (rear) play a part in the balancing of the assembly, they must be installed on the crankshaft when it is balanced. This is unlike an internal balance configuration where the harmonic dampener or flywheel do not contribute to the balance of the crankshaft and are not required to be installed when the crankshaft if balanced. Both methods are used from the manufacturer.
An example of some factory internally balanced engines are Chevy 305 and 350 (2 piece rear seal only!), Chevy 396/427, GM LS-series, and Ford "modular" 4.6. Some examples of factory externally balanced engines are Chevy 400 and 454, Ford 302 and 351W.

I had A 351 C 4V internally Balanced that used a 300 6 cylinder Flywheel and 0 Balance Damper unit. I don't remember how much Mallory they put in the Crank all I remember was every time I asked how it was coming along the $$$$$$ built up.

 

[Eric]

Wally

Thanks for the great explanation. I think you finally connected the dots for me.

If I understand correctly, it seems like making a balancer from a 5.0 (50 oz) into a balancer for a 5.8 (28 oz) would require the machine shop to remove material, not add Mallory. Not having talked to a machine shop yet, this seems like it shouldn't be that expensive, as opposed to adding Mallory, which I know is very expensive.

Eric

 

[Dave Bilyk]

Eric,
a few other points to aid understanding.
It is common for people to incorrectly use the unit oz for unbalance moment (no way would you use a 50 oz balance weight). In this case the correct unit is oz.in (ounces x inches) which, for the 50 oz.in case could be for example, a 10 oz weight at a 5 inch radius.

This is quite a volume of material, 10 oz of steel is about 2.2 cubic inches , but there is normally plenty room on a flywheel to tack weld this amount on if appropriate. Mallory metal is a lot denser, but would only normally be used for internal balancing where it has to go into the limited size of crankshaft counterweights.

Often, the weight is achieved by drilling holes, as in my flywheel which looks rather butchered as a result. 10oz is equivalent to more than 11 1/2"dia by 1" deep holes.

In the externally balanced engine, the belt pulley has the dual purpose of balance and torsional damper.

The reason for all this is that the inherent imbalance of these engines is a rocking couple (see pic) so the unbalance at the pulley is opposite the unbalance of the flywheel. (All seems rather brutal given the weights and forces involved, but it works)

Have a look here for more info.
Crankshaft Balance Factors

Dave

 

[Howard Jones]

As I understand it the main reason that the SBF V8s are externally balanced is that they are designed to have narrower block. The lack of room between the inside rails of the block does not allow enough room for larger counterweights on the crankshaft and prevents a internal balance design. So Ford adds weight to both the crank and flywheel to make up for the missing weight on the crank.

This narrow V configuration has several advantages including lighter weight, packaging, and overall size. The one disadvantage is the balancing requires taking into consideration parts not internal to the motor. If you look carefully at SBF and a SBC you can clearly see that the internal balanced Chevy is wider and if fact a little heavier.

 

[Eric]

I'm very glad I started this thread. I am learning a lot. Hopefully others now and in the future will find this information useful, too.

Thanks Howard for the explanation of why SBFs are externally balanced. I did not know that.

And thanks Dave for the explanation of correct units (oz.in). That really helped my understanding of this whole discussion (bringing it into perfect clarity, in fact). Also, thanks for the link; there's some good information there, too.

Eric

 

[Cliff Beer]

So I have to ask, why is there even a discussion about external balance? In other words, shouldn't the default be that the crank is balanced internally regardless? After all, the counter-weights right on the crank are going to provide a better harmonic balance than an external counter weight (I would be pretty sure that's correct).

So here's another question (just to complicate things a bit more....). Wouldn't a stroker kit likely throw off the balance? I would assume (we all know about assumptions...) that installation of a stroker kit (say 302/331 or 302/347) requires a rebalance of the rotating assembly, yes?

Signed,

Confused.

 

[Bill Musarra]

Cliff,
Not necessarily so. I stroked my 351 Windsor and still had to have the counter weights drilled and mallory weight added to make it internally balanced. My oil pan had a wedge taken out of the side rail that caused a leak for me. It was taken out just in case a stroker kit is being comtemplated, due to the longer or wider throw of the weights. I would imagine you can order the strokers balanced or not, based on preference. Just know that the walls may have to be altered because of what Howard mentioned above. You can also do like I did and it keeps the walls in tact. If you want a screamer to the high limits of revving, I would imagine you would have to have it balanced. Yes, no??

Bill

 

[Dave Bilyk]

In theory, if the reciprocating weight changes, the engine would need to be re-balanced.
BUT
In practice, remember that we are balancing a reciprocating engine, where the intent is to do the best we can under adverse circumstances.
What I mean by this is, (for a single cylinder) that balancing the reciprocating forces in line with the cylinder, introduces imbalance at right angles.
So starting with an unbalanced engine, we will have 100% reciprocating forces in line with the cylinder, and 0% at right angles. Balancing out all the reciprocating mass will give us 0% in line with the cylinder, and 100% at right angles, so we would be no better off.
So the best we can do, is to balance out 50% of the reciprocating mass, so that we end up with 50% forces in line with the cylinder and 50% at right angles.
The rest is down to number of cylinders and configuration, and how the additive forces from individual cylinders cancel. In our case we have static balance and a large couple unbalance to deal with, but no matter how you cut the cake, you can only achieve a 50% balance, not the near perfect balance you can achieve with a purely rotating machine like a turbine or motor.

Taking that into account, my guess is that you can get away with quite a lot without noticing a difference provided that you end up within 10 or 20% of the optimum.

As far as the difference between internal and external balancing is concerned, a 50 oz.in moment at 6000rpm translates to a rotating force of 3190lbf acting at the flywheel, so this introduces a bending moment in the crank that is not there in an internal balance. Provided that you aren't near the critical speed (which you won't be) this won't make any practical difference to vibration. The force may seem large, but given that external balancing is the norm, I guess that it will be quite small in terms of crankshaft stress.

Dave

 

[Howard Jones]

My thinking is that if you intend to build a high performance engine, and ALL of the engines we are talking about on this forum are high performance, it needs to be balanced, after all its not minivans.com is it?

The question of the definition of "balanced" is actually a good one. When I have had my engines balanced I do know that the crank grinding shop that did them was going for a total variance of less than 1-2 grams total. As a reference the old V6 flywheel that I had balanced to use on my 302 was 160 grams out. The remaining imbalance was on the the order of 6-10 grams. Ashland grinding finished the whole thing at 1.3 grams. He said that was the best he could do with that flywheel. He also told me that it would be fine in my application considering I was going to limit revs to about 5900-6000 rpms anyway.

He also told me that as it was, out by 160g's, it would have lasted minutes on a race track.

The factory "pre-balanced" Scat forged rotating assembly kit I am using in the SBC that is going into the SLC was balanced with a Porsche flywheel and a fairly expensive vibration dampener was out a bit less than 10 grams total. This wasn't something that would have failed right away but why not do it right and have it balanced to what turned out to be right at 1 gram when it when together the first time.

I am sure that nobody wants to spend thousands of dollars on very high quality parts and then ruin them because the resulting engine was not balanced. I have spent about 400 dollars each time I had a engine balanced. That's pretty cheap by any measure, especially when I consider then expensive parts I see going into some of the engines you guys are building.

I am sure their are many of you on this forum that really do understand the technical details of correctly balancing a engine. I would love to hear from you. I am sure we could all really learn something considering the talent that frequents this forum.

 

[Cliff Beer]

I guess I'm kind of confused here because with other high performance engines I've work on/with, it's been assumed that each of the crank, the rods, and the pistons are all balanced to within a gram or two. The crank is also ground so there's absolutely zero run out on any journal and then journals polished. Main caps are installed and a line bore is done to match the ground crank journals. With all that done, that's just a base line starting point for a nicely balanced engine. So, an external balance of some sort is just plain foreign to me.

So, please humor me with one remaining dumb question - if I go through the above drill (essentially, a nicely balanced rotating assembly) is there any need at all for an external balancer/dampner???

Signed,

Still Confused.

 

[Howard Jones]

In the case of a typical as designed SBF the rotating assembly INCLUDES the dampener and flywheel. The entire assembly is then balanced together.

A SBC on the other hand does not include the flywheel and dampener as part of the rotating assembly when balanced. The flywheel as well as the dampener are neutrally balanced separately. This allows for easy replacement of either and remaining within balance as long as the new flywheel for instance is again separately naturally balanced.

You are correct in that the rods/rod caps, piston pins and pistons are matched to equal weights individually. Then assembled and double checked again for equal weight. Then, in the case of a SBF, the crank, flywheel, dampener, clutch pressure plate and belt wheel are balanced together. So when you put all the pieces together in the block it's "a balanced engine"

 

[Dave Bilyk]

Cliff,
the external balance is absolutely necessary to partly counter the reciprocating mass effects. You can achieve the same by internal balancing, but find it difficult to get enough counterbalance in there as per Bill and Howard's posts.
I think of the big picture in the following way, forget the reciprocating masses for the moment, and just consider the rotating masses without any external balance.
If we took the crank and balanced it at the counterweights, then added the flywheel and balanced there, then the clutch, then the pulley, balancing at each stage, we would have a perfectly balanced rotating assembly, and could achieve tight limits with no need for external balance. However, the engine would vibrate badly because the reciprocating masses have not been accounted for.
So where the need for external balance comes in, is for the reciprocating masses. In the 90deg V8 configuration, these result in a residual rocking couple (as per my previous diagram) that is countered by the 50 oz.in (or 28) external balancing.

However, there is another really important point that needs to be appreciated to get a more compete picture. Because the reciprocating forces are in only in line with the cylinder, and any balancing we do has an effect at right angles too, the best we can do is to balance 50% of the reciprocating masses. If we balance 100%, we only swap the balanced forces from in line to at right angles. By balancing 50%, we reduce unbalance by 1/2 and that is the best we can do, if we go further, all that happens is forces at right angles increase and the balance gets worse. How the forces ultimately balance out is down to engine configuration, in our case we are left with the rocking couple, so if we do a 50% balance and end up with a 50 oz.in counterweight, then there is still 50 oz.in left in there that can't be balanced. This is true whether you go internal or external.

I can reinforce this point by looking at the balancing process, which is to add counterweights to each throw. These counterweights are typically half the reciprocating mass, and yes, with the counterweights on, we can balance it down to 1gramme or whatever, but there is effectively 50oz.in still left in there, so what we are actually doing is balancing to a residual of 50oz.in, with an accuracy of 1 gramme (0.2 oz.in on a 5in radius).

I should explain that I have many years experience resolving balancing issues in our factories and global service centres, from small 15000 rpm down to 10ft diameter 120rpm rotating machines, so I have to understand the fundamentals very well.

The attached diagrams visualise the reciprocating unbalance, and the effect of the optimum 50% balance etc
Sorry to bang on about this like some boring lecture, but these points are important to understand the true nature of this balancing process.

Dave