Balancing Con Rods

[Fast Eddie]

i got a new set set of rods for my type4 from european motorworks. they look good and i am happy with them, but i thought i would weigh them and found  about 5 grams difference between them the lightest and heaviest. 2 weigh 515g and 2 520g i think.

is it worth balancing them? if so, what is the procedure, big end first? or little end first?  or different?/?


cheers.

[Jesse/DVK]

You could use those of the same weight at the opposite cilinders.

[Bruce]

....is it worth balancing them?

Yes, you must balance them.  A 5g variance is the stock spec limit.  That's good for an engine that doesn't go over 4500-5000 rpm.  Since you're likely to rev higher, you'll need to balance them.
The proper way is to take them to a shop that can balance them.  Needed are special fixtures to support them while weighing each end.

The ghetto way to balance them is to take the caps off and match them.  Then match the other half.

[Fast Eddie]

i am making a support for both ends at work, which i can hold in a vice. i have scales accurate to 0.5grams.
i have watched different methods of balancing, i have paid for it to be done before aswell. i just want to do it myself this time. 
the thing i want to know is which end to balance, like i said, i have watched different people and on the net, some start by weighing the whole lot and then just taking the difference from one end. others seem to weigh both ends and match them.. what would you do??
cheers 

[JIMP]

Eddie

I have recently build a fixture of my own, re;atively easy to find materials, some half an hour work on a lathe and about two hours to complete, seems to me working really good -because of the bearings probably used-, I'll try today to make some photos and upload them for you, cheers

Friendly

Dimitrios

[Mike Lawless]

You should balance both ends. Each end should weigh the same as the others, and the rod should weigh the same overall.

[Bruce]

i am making a support for both ends at work, which i can hold in a vice.

To verify your fixture, load your rods and measure the ends. Then reload the rods again to see if you get the same readings.

[JIMP]

Eddie, sorry for the delay, here are some pics for you, hope they help a bit

[Fast Eddie]

thanks for the pictures Dimitrios, very helpful.
Quick question about the set up, and all the others that i have seen, why is it necessary to hang the rod with the chains?
can they just not be supported at one end?
cheers again.

[Dr P.]

The idea with the chain is to make it hang as free as possible. If the supporting jig is not well built it will be impossible to get consistent readings. Due to this I made a dead simple balancing ijg. It is a piece of wood with a piston pin at a height that makes the rod horizontal. The "feet" of the jig consist of 3 wood screws (to make it always support on all 3 feet).

It works only with one length of conrods (screws have to be on the center line of the big and small end respectively). The readings of this one are much more consistent compared to a hanging version i made.

Balancing jig

Edit: forgot to mention that the supporting screws are in the wrong position on the pictures. The pics were taken from the first prototype I made without access to the conrod. Just guessed the initial location.