I have always read that aftermarket rods/pistons are close enough in weight to not need balancing after assembly. Even so, I decided I would at least pair up the heaviest rod/lightest piston to get as close as possible. Well, the Wisecos came pre-weighed ranging from 270.2g-270.5g; so I only needed to weigh the Eagles.

530g 530g 520g 530g

10 grams difference!! Same part number, same physical size, different stampings on the big end of the rod though. Does anyone know what the different stampings mean? They are marked ZU, ZU, ZV, ZU.

Eagle is taking care of me and sending me new rods; but if I had put the motor together I imagine it would have worked itself to pieces rather quickly or at least ate the bearings up. The guy at eagle said 1 gram variance is the most they allow.

Any engine builders thoughts on max variance in weight of the rotating assembly?

 

The stamps classify the rods into different weights so they can be matched. Someone without a good eye mixed a ZV in with the others.

BTW, 10 grams difference won't really affect much. You should see how poorly balanced a rotating assembly gets when it sloshes around in oil.

 

<TABLE WIDTH="90%" CELLSPACING=0 CELLPADDING=0 ALIGN=CENTER><TR><TD>Quote, originally posted by beepy &raquo;</TD></TR><TR><TD CLASS="quote">The stamps classify the rods into different weights so they can be matched. Someone without a good eye mixed a ZV in with the others.
</TD></TR></TABLE>

The guy at eagle tells me that the stamps arent an indication of weight, rather a indication of manufacture date.

 

When a machine shop balances pistons and rods do they just weigh them on a scale and remove material anywhere from the piston and rod? Or is their a specific spot on the piston and rods they remove the material from?

 

<TABLE WIDTH="90%" CELLSPACING=0 CELLPADDING=0 ALIGN=CENTER><TR><TD>Quote &raquo;</TD></TR><TR><TD CLASS="quote">a specific spot on the piston and rods they remove the material from</TD></TR></TABLE>

On the rods there are pads on either end of the rod. They grind off material there. Pistons are usually not balanced, but are matched.

 

wow

 

beepy how would they know what side to take the weight of the rods im wondering if just using a digital scale if i could do this myself? As far as the pistons so they just weight match them all correct?

 

There is a fixture that is used to measure the piston end of the rod first.Then that end is balanced.Then the total weight is checked and is balanced buy removing material from the crank end of the rod.It's not something you can do with out the fixture.
Glenn

 

All mine are ZV..
Hmm... Measuring tonight....

 

usually a machine shop will shave on the piston skirts to balance them, it is critical to have the lower end balanced, especialy if you are building it with new parts. I would check everything, because you want to get what you pay for.

 

I am bumping this, I think more people need to see it as I know ALOT of people who have put aftermarket bottomends together without balancing.

 

Not only is balancing a good idea for power purposes, but it will make things last a lot longer. The bearings wear according to where the weight is thrown. Most of the time a bearing is spun because something is out of balance or is thown out of balance. If you are rebuilding a motor, hopefully, you want it to last. Even if you are going back with stock internals it wouldn't hurt. Are you rebuilding the motor because it has spun a bearing? Think about this.

 

<TABLE WIDTH="90%" CELLSPACING=0 CELLPADDING=0 ALIGN=CENTER><TR><TD>Quote, originally posted by civicdonwon &raquo;</TD></TR><TR><TD CLASS="quote">Most of the time a bearing is spun because something is out of balance or is thown out of balance.</TD></TR></TABLE>

I don't think I'd go that far... hehe.

Most of the time a bearing is spun... because of oil starvation.

 

<TABLE WIDTH="90%" CELLSPACING=0 CELLPADDING=0 ALIGN=CENTER><TR><TD>Quote, originally posted by civicdonwon &raquo;</TD></TR><TR><TD CLASS="quote">usually a machine shop will shave on the piston skirts to balance them, it is critical to have the lower end balanced, especialy if you are building it with new parts. I would check everything, because you want to get what you pay for.</TD></TR></TABLE>You would never remove material from the skirt when balancing a piston. There are better spots.

 

so what's your take on a 10g weight disparity Earl? Also would weight matching cheap rods on a scale at home do more harm than good? Maybe just taking weight off the big end or something to bring them closer.

 

<TABLE WIDTH="90%" CELLSPACING=0 CELLPADDING=0 ALIGN=CENTER><TR><TD>Quote, originally posted by Bailhatch &raquo;</TD></TR><TR><TD CLASS="quote">so what's your take on a 10g weight disparity Earl? Also would weight matching cheap rods on a scale at home do more harm than good? Maybe just taking weight off the big end or something to bring them closer. </TD></TR></TABLE>

I would like to get earl's outlook as well.

I wasn't going to attempt to remove any material myself, I was just going to match the heaviest piston with the lightest rod.

I think beepy had a good point when he mentioned the weight of oil clinging to the crank; although I would think it is a pretty much uniform coating. Maybe it isn't such a big deal, but even 1 gram difference becomes exponentially more and more stressful with every rpm.

 

<TABLE WIDTH="90%" CELLSPACING=0 CELLPADDING=0 ALIGN=CENTER><TR><TD>Quote, originally posted by SnOOpY-NO &raquo;</TD></TR><TR><TD CLASS="quote">All mine are ZV..
Hmm... Measuring tonight....</TD></TR></TABLE>

533g, 533g, 533g, 533g

Phuu.....

 

you guys have got me wondering now, I will weigh them as soon as I pick them up from the shop.