Rod balancing

[boosted79]

Thought I'd post this here for general info, i have a build thread in the turbo forum.

I balanced the pistons and rods, all to within 0.1 g. Overkill for a street machine for sure. The spread on the total rod weights was 3.7 g from the factory however on the small ends the spread was 7.2 g. Now to finally get this thing together.

[cgarr]

Nice setup, you make that? is it pretty consistent?

[Tippy]

Moment weight, the only way

[boosted79]

Yes, I made it. I started out with the chain just on the big end and with a rigid support just resting on the scale for the small end. It was difficult to get repeatable readings. So I went with the chain on both sides. You want the center line of the rod horizontal and the chains parallel. The readings are not always perfectly repeatable for the small end weight but are within a few tenths. I can tell when it is right. The scale is absolutely repeatable within 0.1 g. The easy way to use this:
1) record the total weight of each of the rods
2) now take several readings of just the small end of each rod. I take six. Then take the average of all the readings for each rod to get the small end weight.
3) pick the lightest small end weight, that's what you want to match the other small ends to.
4) now take the total weight of the rod and subtract how much needs to be removed from the small end. That number will tell you how much the rod will weigh after the small end is balanced. This eliminates having to weigh just the small end again and eliminates any repeatability error with the chains. You just weigh the whole rod. Example, say you need to remove 3 g from the small end as determined in step 3. The beginning weight of the rod is 694 g so after the small end is balanced the rod will weigh 691 g. You grind the small end until the rod weighs 691.
5) after the small ends are done then you pick the lightest rod and grind the big ends of the heavy rods to match the lightest rod and you're done.

I'll get some more pics of the rig if anyone is interested.

[Steve F]

Originally Posted by boosted79

I'll get some more pics of the rig if anyone is interested.

Thank you, I would like to see some more pics of the set up please

[ganun]

I equalized the rod caps, then did the rods top and bottom, but just to the gram, ...some like you said were several grams heavier than the lightest......Just to the gram made an amazing super noticeable difference in engine smoothness. Before, a roughness around 4k now smooth all the way to red line.

[boosted79]

A couple more pics. I probably went overboard on the big end chain length, it's 36",LOL. When I couldn't get repeatable readings with just a solid support resting on the scale for the small end I doubled the chain length on the big end. The longer the length the less the error from not having the chain absolutely plumb. It made a difference but getting rid of the solid support and using a chain for the small end also really made it repeatable to a few tenths.

[Mark Henry]

Balancing rods can become a dog chasing it's tail affair, I stopped looking for perfect and just aim for pretty damn close.
You will never feel +/- 1g.

[cgarr]

Originally Posted by Mark Henry

Balancing rods can become a dog chasing it's tail affair, I stopped looking for perfect and just aim for pretty damn close.
You will never feel +/- 1g.

LOL, yea don't let perfect get in the way of done!