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Buildengines101 said:
Can I eliminate the balance shaft on 96 "W" 4.3 V6 if I balance the rotating assenbly & what bobweight total should I use 50%????
It will shake more than it has because a 90* V6 is out of phase 120* firing with 90* vee angle. All the old V6s were like this, though.

Bob-weight, definitely NO.
Use the proper calculated bob-weight for a 120* crankshaft 90* V6 and spin balance to 0+ grams.

I think that you are mistaken in your terminology. If you used 50% of the calculated bob-weight, you would have to cut a tremendous amount off the crank counter-weights.
 

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I`m not sure of the balance shaft engines, but the non balance shaft engines balanced with a 36% bobweight. I just had my 4.3 crank balanced to this spec. Thanks to Machine Shop Tom for this information.
 

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DoubleVision said:
I`m not sure of the balance shaft engines, but the non balance shaft engines balanced with a 36% bobweight. I just had my 4.3 crank balanced to this spec. Thanks to Machine Shop Tom for this information.

That means 36% reciprocating?
 

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The balance shafts are not there because of an imbalance in the reciprocating mass, they are used to counteract the imbalance inherent in a 90 degree V6 motor. The problem is that even with split crank throws (as pioneered by Buick on the even-fire V6) you can't get firing pulses that are evenly spaced. The split crank throws make it better, but it isn't perfect.

A 60 degree V6 and a 90 degree V8 are balanced by design (firing pulses are 120 deg or 90 deg apart, respectively). On a 90 deg V6 this is not the case. No amount of crank balance weight will solve this problem. Now, you may not care about the vibration, but it will be there.
 

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so all the 4.3L have them ? i thought it wasonly the Z vin code ones that did, like in my brothers 92 s-10

hmmm
interesting

so if the firing pulses(firing positions??) ar enot 90 or 120 degrees apart on the old 90 degree v-6 engines(200, 229, 262) then what are they ? how far off from 90 or 120* are they ?

interesting...


ive read somewhere before that some years were even and some were odd


i dont rememberhow or why though, i read it somewhere though, hmmm

good thread :D
 

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fast68 said:
so all the 4.3L have them ? i thought it wasonly the Z vin code ones that did, like in my brothers 92 s-10
That I'm not sure of. I'm an Olds guy normally. GM has been going through a phase of trying to "refine" their engines for smoother operation, so I think the balance shafts have been creeping in over time.

so if the firing pulses(firing positions??) ar enot 90 or 120 degrees apart on the old 90 degree v-6 engines(200, 229, 262) then what are they ? how far off from 90 or 120* are they ?
As I noted, the ideal V6 should have firing pulses ever 120 degrees of crank rotation. The "odd fire" V6 with 90 degree cylinder bank angle uses a crank with three rod journals, each 120 degrees apart. This yields firing pulses that are 90-150-90-150-90-150. You can see where the vibration comes from. In mid-1977 Buick went to a crank that "split" the rod journals on the crank. Unfortunately, this weakens the crank, so they couldn't move them far enough to get firing pulses that were exactly evenly spaced, but it was a lot smoother than the original motor. Note that the odd-fire motors use a distributor cap that looks like a V8 cap with two wire missing. The even-fire motor uses a cap with all six wires evenly spaced.

ive read somewhere before that some years were even and some were odd
For the Buick motor, that was 1977. I don't know when Chevy did it with the 4.3 or if that motor used split crank throws from the beginning. Conventional thinking is that a truck can have a rougher running motor than a car, but today's truck buyers want their trucks to be just like a car, hence the need for balance shafts.

Note that the whole reason for building a 90 deg V6 is so you can machine and assemble the motor on the same line as a V8. When Buick bought the V6 back from AMC in 1974, they increased the bore to 3.8" to match the Buick 350 V8 and built the motors on the same line. Chevy did a similar thing with the 4.3, which is an SBC with two cylinders missing.

Of course, GM has replaced the 90 deg V6 with an I6 in their SUVs because the inline configuration is inherently smoother running for a six.
 

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joe_padavano said:
The problem is that even with split crank throws (as pioneered by Buick on the even-fire V6) you can't get firing pulses that are evenly spaced. The split crank throws make it better, but it isn't perfect.


Offset ground cranks do actually fire at an even 120.

But the rotational imbalance is still there.
 

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xntrik said:
Offset ground cranks do actually fire at an even 120.

But the rotational imbalance is still there.
I know that's the desire, and maybe the current offset cranks are designed to provide this but I distinctly recall the article about the even fire Buick in 1977 that said they didn't quite get the pulses evenly spaced. This may have had something to do with the then-current rod bearing size or it may just be my bad memory after 30 years...
 
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