Dynamic Balancing Jeep/Dodge 4.7

[rcull]

I have been asked to balance a Jeep 4.7 V-8 assembly. It has rod separators on the throws. Is there a recommended work around for this? I have a set of V-6 weights which will fit in the rod positions. Can I just use 4 of them and place them all on either the front or rear rod positions?

Thanks

[rcull]

Sorry if I used poor terminology:(

[BillK]

Bob,
That is the first time I have seen one of those. Definitely strange. You could probably put all of the bobweights either to the front or back and be fairly close. When I first bought my balancer over 20 years ago I was told to put them all towards the front. I did it that way for a year or so but then started to put them in the middle. I did some experimenting and it definitely affects it but not as much as you would think.

I have a small block Chevy crank on the balancer right now that I had finished last night before I left. I just moved all of the bobweights from the middle to the front of the journals and it only made about 1/2 gram difference on both ends.

[MotionMachine]

Bill, I'm thinking that by "front and rear" positions, he means put bobweights on the front and rear throws and leave the 2 center throws empty?

I think borrowing a couple more bobweights would be a good idea.

[MotionMachine]

I get it now, misunderstood it the first time. I've also messed with the position on the throw, seems to make little if any difference at all.

[PackardV8]

I've also messed with the position on the throw, seems to make little if any difference at all.

Most Operator's Manuals or instruction help functions specifically state the relative position of the bobweights is of no concern.

Anyone ever watch a youtube video where the instructor centers the bobweights with a caliper and levels them with a Starrett machinist level?

BTW - what is the theoretical and practical benefits of the divider on the rod throws? Wonder why this is the first application we've ever seen of it?

[rcull]

Yes, I was thinking BillK's suggestion was a satisfactory approach. I was told, for normal crankshafts, to put them towards the center, with a consistent error from one end (using a spacer).
My concern was, like Bill, I have never seen a crank like this before and it forces the weights to be mounted at the extreme. Because of the extreme aspect, I was wondering if, perhaps there was a better practice approach to the job.

I will try set up my V-6 weights to see what I find!

I located the weights against the dividers.

Findings on throw positions 1,3,5,7:
Left plane unbalance 21.5 @ 16 , right plane 28.0 @ 178

Findings on throw positions 2,4,6,8:
Left plane unbalance 19.9 @ 23 , right plane unbalance 27.4 @ 176

Findings on throw positions 1,3,6,8 ( I was moving the weights and thought this might be interesting):
Left plane unbalance 41.4 @ 230 , right plane 45.4 @ 71



Thanks

[rcull]

I did a plastersine balance with the bobweights on 1,3,5,7 and then moved the weights to 2,4,6,8 and the balance was still good.

I suspect that is a satisfactory way to go, but it would be nice to have some assurance:)

[PackardV8]

I did a plastersine balance with the bobweights on 1,3,5,7 and then moved the weights to 2,4,6,8 and the balance was still good.

I suspect that is a satisfactory way to go, but it would be nice to have some assurance:)

Have you read the operator's manual for your machine? As previously stated, most will say the position of the weights on the throws are not critical. Then, that you impirically confirmed this isn't good enough?

[ec1]

Have you tried just putting the regular V8 bobweights right over the ribs and kind of pretend they aren't there? Maybe they will still fit?? Makes me hate these Chrysler engines ending in .7 even more!

[ec1]

What I have found on a V8 is that the weights need to be centered (left to right as you look at the crank in the machine) for everything to be correct. You can rotate the orientation of the weights any place, but as far as front to rear, centered is the accurate way. Same thing with external harmonic balancers, they need to be spaced the same as when running. I keep an bunch of old timing gears that I honed out for a slip fit as spacers.

[Dave Koehler]

Centered is correct. My own tests long ago prove that out.
As to how to pull this off my suggestion is to make some aluminum spacers (bearings) and use your V8 BWs in the normal fashion.
or
Round up a couple more skinny V6 BWs.
or
Machine a groove in the V8 BWs to clear and auto center on the dividers. Actually that would not be too difficult to accomplish.
(I assume the total width of both journals and divider are more than the width of your V8 BWs)

Rcull: For future reference can you tell me the width of of the journal and the height of the divider rib?

[BillK]

Centered is correct. My own tests long ago prove that out.

Dave,
I always center but ..... next time you have a crank on the balancer and finished, move all of the bobweights to the front of each journal and spin it and see what you get. I don't think the difference will be worth the trouble of making spacers, compensating for the weight etc etc. Usually not more than a gram or so at a 3" radius.

[PackardV8]

Centered is correct. My own tests long ago prove that out.

Dave,
I always center but ..... next time you have a crank on the balancer and finished, move all of the bobweights to the front of each journal and spin it and see what you get. I don't think the difference will be worth the trouble of making spacers, compensating for the weight etc etc. Usually not more than a gram or so at a 3" radius.

Both of you have done more custom balancing than most any here, but while centering is easier to replicate, agree with Bill, at least on our old Winona and middle-age Pro Bal, it doesn't make a great deal of difference. We spun the bobweights front, rear, centered, squared, random and results were within the margin of repeatability.

[Dave Koehler]

I can only say that I see enough of a difference to be wary of playing games with lefty, righty positions.
FWIW I do know that the modern hard bearing machines show more variation than the older soft bearing, swinging machines.
I do not know if it is a digital vs analog or a mechanical reason but there it is.
Does it matter? Don't know, don't care. I can only go by what consistently works.
For me center is critical for repeatability when the BWs have to be R&R for heavy metal or radical CW mods.