Balancing

[Trev]

Just looking at my new Lunati Pro Billet rods
Of course I will have the whole assembly balanced but just looking at the rod weights
They vary a fair bit more than I would have expected

Reciprocating Weight 185 gms
Rotating Weight 457 gms
Total weight 642 gms

Reciprocating Weight 186 gms
Rotating Weight 460 gms
Total weight 646gms

Thats a 6 gm difference
I thought that most manufacturers tried for a +/- 1 gram

Oh ye
is the reciprocating weight the piston pin end and the Rotating weight the rod bearing end
And do balancers go to the trouble of removing caps and make the weights the same or just keep the cap on and make it the same.

Trev

[dart441]

MY Pro Billets had 7 identical and 1 at +3 grams. I thought they could have gotten them closer. Balancer took care of it. Very nice rods and Yes, cheaper than Carillo.

[CNC BLOCKS]

Just looking at my new Lunati Pro Billet rods
Of course I will have the whole assembly balanced but just looking at the rod weights
They vary a fair bit more than I would have expected

Reciprocating Weight 185 gms
Rotating Weight 457 gms
Total weight 642 gms

Reciprocating Weight 186 gms
Rotating Weight 460 gms
Total weight 646gms

Thats a 6 gm difference
I thought that most manufacturers tried for a +/- 1 gram

Oh ye
is the reciprocating weight the piston pin end and the Rotating weight the rod bearing end
And do balancers go to the trouble of removing caps and make the weights the same or just keep the cap on and make it the same.

Trev

642 too 646 is only 4 grams ,On our balace card the rod rotating is the big end and that weight and the rod bearing weight is figured twice everthing else is figured in only once.

If your machinest balanced to the heaviest rod and piston that would make it over balaced which is good that won't hurt nothing as you should NEVER under balance any rotatators.

Smokey once told me that balancing is an imperfect science. And I think he is right.

[bill jones]

-One way to possibly fix the problem without having to actually remove any metal is to pair up rods so that one light one and one heavy one end up on the same rod journal.
-Example is if you take the 457 and the 460 and average that you get 458.5 as the average.
-if you can match up pairs that average 458.5 then you wouldn't have to rebalance.
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-One problem of grinding to rebalance is you ruined the shotpeened surface where you grind off the weight, so you really should have those areas reshotpeened to do it right.
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-When I balance rods I use what I call a balance factor for the rods.
-This is where you take the top of the rod-use that number once and add bottom weight twice to get the balance factor.

-your examples would be:

-rod #1 is 185 plus 457 + 457 = 1099 is what you'd end up with that rods contribution towards the total bob weight if you are doing a 50% balance.

-rod #2 is 186 plus 460 + 460 = 1106.

-So you can see that #2 rod is 7 grams different from #1 when it comes right down to the actual bobweight factor.

-if you had both of these rods assembled as a pair the total would be 1099 + 1106 = 2205.
-So 2205 is what you'd try to get matched up within the 4 pairs of rods.
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-I would weigh each rod both ends and then see how much variation you have among the 8 rods, and then see if you can pair them up real close.
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-an example of a bobweight and how this all entertwines is:
-450 piston
-120 wrist pin
----4 pin locks
---45 piston rings
-185 top of rod #1

-804 is the total reciprocating weight

-457 bottom of rod added in once
-457 bottom of rod added in again
---45 one pair of rod bearing shells added in once
---45 one pair of rod bearing shells added again
----6 (guesstimate for oil weight inside the oil galleys)

-1010 is the total rotating
---804 reciprocating is added
-1814grams would be the total bobweight you use to balance the crank.
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-I don't think it matters one litttle bit how you end up with the 1814 meaning that if you changed one wrist pin to a 125 and then lightened the piston 5 grams you still get the same total.
-or if you put a 7 gram heavier piston or pin combination on rod #1 you still get the same total as the heavier rod with a 7 grams lighter piston/pin.
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-When you get to looking at the rod balance problem here, and if you read this explanation right, you'll see that whatever the rod is out of balance on the big end is twice as important compared to the reciprocating components.
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-If you do match up the components you need to engrave the proper cylinder numbers onto the components so they end up always going back together during assembly.

[Wolfplace]

Trev,
I have to agree with you.
In my opinion, there is just no reason they cannot control weight closer than 6 grams,, hell, Scat does a better job than that on their $250 rods.

That said, I have no problem whatsoever removing weight from above the pin around the complete circumference & removing weight at the sides of the cap & rod where you would normally etch your numbers.
I have been doing this for 30+ years & never had a problem with it.
Never seen a rod break in these locations unless something else happened first.

I prefer to hold the weights to within 1 gram unless you have to sacrifice strength which is not the best plan.
Don't have a problem mixing & matching pins to pistons if necessary but most of the pins are pretty good these days with a few exceptions.

And I agree completely with Carl regarding using the heaviest parts for your bobweight if you have a difference.
I think it is well excepted that a little too much counterweight is better than too little

[Dave Koehler]

Actually you are only 3 grams apart on the big end and 1 gram apart on the small end.

This is what I would consider a good factory average out of the box. We all have seen bigger spreads in supposedly factory "matched" sets.

Is it as good as it should be for the money spent. No But that is what the balancing procedure is supposed to take care of , by either matching up pairs or a touch here and a touch there to bring them down to whatever spec you subscribed to.
Actually I am tickled when I see them that close out of the box. It means I don't have to spend more time finessing them down.

Worst problems I have with rods are aluminum rods. Most of the time you have to either do the match process or just balance to the heavy side as noted. ( 3 gram spread would be a great day)
The other is the almost impossible task of getting a replacement rod that is the same of a touch heavier than the original.

I am amazed from time to time that some rod company does not have the setup to weigh each end when you call in with the BE and SE weight targets.

Have a safe race
Dave Koehler
www.koehlerinjection.com