My 2wd Mountaineer has a balance shaft...

[cross6]

Boroscoped my engine today through the crank snout opening in the timing cover to check the primary chain assembly and discovered a chain behind the primary going down to the oil pan.

So I have a balance shaft.


Do these engines have the VIN # on them anywhere? I bought the truck with ~ 90K. I do see a engine date code which is only a few months before my truck's assembly date so that seems to check out, of course they may have re-used the old valve covers...

 

[2000StreetRod]

engine VIN location

VIN location

Some early Mustangs came from the factory with balance shaft engines even though there are no 4WD Mustangs.

 

[imp]

VIN location

Some early Mustangs came from the factory with balance shaft engines even though there are no 4WD Mustangs.

Stupid me! Please explain what the V-6 balance shaft would have to do with distinction between 2WD and 4WD?

I am under the impression that any 60-degree V-6 engine inherently generates undesirable vibration harmonics, which cannot be cancelled through crankshaft weighting alone, thus, the balance shaft.

Am I wrong? imp

 

[2000StreetRod]

engine balance

Two types of imbalance associated with the SOHC V6 engine are rotational imbalance and reciprocating imbalance. The crankshaft counter weights reduce rotational imbalance. The balance shaft is used to reduce reciprocating imbalance. That is one reason that the balance shaft rotates much faster than the crankshaft. A symmetrical opposing (flat) engine needs no balance shaft because the reciprocating forces of one piston are offset by those of an opposing piston.

I remember many years ago as inline four cylinder engine displacement increased from year to year that there was a common belief that two liters was the maximum size possible due to vibration concerns. The industry incorporated balance shafts to exceed the two liter limit. Some engines even had two balance shafts rotating in opposite directions.

4WD associated components are all rotationally balanced. I suspect that Ford chose to implement the balance shaft for reduced vibration for customer satisfaction rather than increased serviceability. Ford produced millions of V6 engines (OHV and SOHC) with no balance shafts and no associated recall notices due to premature failure. I'm not aware of any technical service bulletins regarding premature crank failure related to the absence of a balance shaft. Some standard shift performance enthusiasts purchase lightened flywheels for reduced rotational mass and increased throttle response. The negative impact is a slightly less smooth idling engine. I think the balance shaft issue is an analagous trade off.

 

[imp]

"I suspect that Ford chose to implement the balance shaft for reduced vibration for customer satisfaction rather than increased serviceability..."

2000, thank you kindly for your answering. Your knowledge must date back pretty far, like mine, although I never was much of a V-6 fan.

Somewhere in one of these forums, possibly not this one, the balance shaft question was hashed and re-hashed, until it finally died. One guy disconnected the shaft, and claimed absolutely no difference could be felt. In my own mind, I can imagine unbalanced forces reducing crankshaft bearing life, but probably having little or no effect on actual crankshaft life. imp

 

[cross6]

Balance shafts are not for rotating or reciprocating balance. NVH concerns only.

Balance shafts are for non-sinusoidal forces. An engine can be balanced in regards to reciprocating and rotational assemblies and still produce second order vibrations. A balanced engine means that it remains balanced through one revolution. But there can still be non-sinusoidal forces that occur out of balance every 1/2 rotation, every 2 rotations, every 3 rotations, etc.

Inline 6 is the best example of this. They actually produce more second order vibration at high rpm than 60 degree V6s. Despite being more naturally balanced.

I can only assume Ford made the choice because 4WD will spend more time in high rpm ranges.

Vibrations from non-sinusoidal forces are non existent at idle and increase exponentially with RPM. If you double the RPM you quadruple the NVH from second order imbalance.

Flat 4s do produce less second order vibrations but are actually less balanced than inline 4s due to the offset connecting rods which increase rocking. Engine balance and the need for balance shafts are not related usually. More to do with RPM operation range, displacement, motor mount and drivetrain design.

 

[imp]

Balance shafts are not for rotating or reciprocating balance. NVH concerns only.

Balance shafts are for non-sinusoidal forces. An engine can be balanced in regards to reciprocating and rotational assemblies and still produce second order vibrations. A balanced engine means that it remains balanced through one revolution. But there can still be non-sinusoidal forces that occur out of balance every 1/2 rotation, every 2 rotations, every 3 rotations, etc.

Inline 6 is the best example of this. They actually produce more second order vibration at high rpm than 60 degree V6s. Despite being more naturally balanced.

I can only assume Ford made the choice because 4WD will spend more time in high rpm ranges.

Vibrations from non-sinusoidal forces are non existent at idle and increase exponentially with RPM. If you double the RPM you quadruple the NVH from second order imbalance.

Flat 4s do produce less second order vibrations but are actually less balanced than inline 4s due to the offset connecting rods which increase rocking. Engine balance and the need for balance shafts are not related usually. More to do with RPM operation range, displacement, motor mount and drivetrain design.

Most interesting! Thank you for the info! I would add, be careful about calling reciprocating piston motion "sinusoidal": it is not. Manufacturers bore the wrist pin holes in the pistons off-center, to bring the motion more closely into true sinusoidal. That's why pistons have markings to properly orient them; installed backwards, the problem is worsened.

Another term used is "Simple Harmonic Motion" (SHM). We had a Calculus Textbook in college which stated pistons move in an engine in SHM. A young guy just out of the Army questioned it, the instructor revealed (the next day, after researching it), the guy was right! Army training must be pretty good!

imp

 

[cross6]

Most interesting! Thank you for the info! I would add, be careful about calling reciprocating piston motion "sinusoidal": it is not. Manufacturers bore the wrist pin holes in the pistons off-center, to bring the motion more closely into true sinusoidal. That's why pistons have markings to properly orient them; installed backwards, the problem is worsened.

Another term used is "Simple Harmonic Motion" (SHM). We had a Calculus Textbook in college which stated pistons move in an engine in SHM. A young guy just out of the Army questioned it, the instructor revealed (the next day, after researching it), the guy was right! Army training must be pretty good!

imp

Yep. Even my explanation (and understanding) is really simplistic. I read a huge article once on second order vibrations and it gets crazy like how two pistons moving together are balanced through 1 revolution but out of balance when looked at in 2 revolutions because one will have more inertia than the other and all this stuff.

Lack of balance shaft definitely will not hurt the crank or mains. Motor mounts maybe.

The crank is imparting these non-sinusoidal forces to the block. Then the balance shaft imparts its forces to the block to cancel the vibration. Either way, the crank still experiences the forces. It's like noise cancelling headphones. The noises are still being produced, just cancelled before you can feel them.

 

[imp]

"The crank is imparting these non-sinusoidal forces to the block. Then the balance shaft imparts its forces to the block to cancel the vibration. Either way, the crank still experiences the forces. It's like noise cancelling headphones. The noises are still being produced, just cancelled before you can feel them."

Most interesting explanation! Thank you for it! In a similar way, we who studied Electrical Engineering, run into harmonics all the time. Generally, harmonics appear at amplitudes (strength) less than that of the original waveform, but often out of phase, as you describe. One thing, resonance, is found both in electricity and mechanics. It can be good or bad. Like the soldiers marching across a bridge in-step, creating a resonant effect which can collapse the bridge. imp