connecting rod balance

[Testarossa]

I just weighed the reciprocating bits for the T rebuild. The Gilardoni pistons with pins differ by only .1 gram.

But the connecting rods without the new bearing shells are 583.8 and 597.0 grams -- a difference of 13.1 grams,. That seems like a lot, though it's only 2% of the weight of a rod. What's the allowable difference?

As near as I can tell, the difference in small end weight is only 3.5 grams.

[Tom H]

 

"Hey! [Callahan turns around] I gots to know!"

Tom

[wirespokes]

The work I've done like this has been with airheads, and they've run smoother getting everything balanced. I don't know how important or how much of a difference it makes, but I'd balance them. It's easy enough removing some of the casting seam on the heavy one.

[oldbike54]

 The experts might disagree , but I was taught to get them within 1 gram of each other .

 Dusty

[Testarossa]

Correct me if I'm wrong:  The big end weight shouldn't matter much because the two big ends rotate together as a single mass.

The small ends reciprocate with the pistons so they're important, and I'll try to match them by taking off some material from the heavier one. What matters is how to weigh them. If I cut a block of wood the same height as my scale, put the big end there and center the small end on the scale, will that be a reasonable weight? With that system I get 2 grams difference between the small ends.

[RinkRat II]

 The weights at each end do matter. remove material only at the flats at the bottom of the big end and the top flat of the pin end. With your setup, flip the rod around to see what the big end difference is. Allowable total difference shold be less than 2 grams

   Paul B

[canuck750]

When I have had Guzzi cranks reground I take the rods in to be balanced, costs me about $30 a rod, seems to be worth it.

[Roy gardner]

Have a look in your V7 Sport/850T Workshop Manual. Pg 20 states "conrods c/w nuts & bolts should be the same weight.Max permissible difference; 3 grams" Then page 79, which is 850T differences, states "Static balancing of crankshaft is obtained by applying a weight of 1.586 to 1.616 Kg"

Clearly the latter requires knife edges or wheel balancing rollers similar to what we used to balance cylindrical grinding wheels, or give it to an engine recoditioner to do on a dynamic balancer.
With 40 years of ownership & constant wrenching I still havent balanced a Guzzi crank or rods yet, but will start with my V7 Sport later in the year. However, here is what I use for Vincent rods & will modify it for Guzzi ones soon.

 

[Antietam Classic Cycle]

I guess I got lucky - the rods from my V700 were identical in weight, even end for end. Piston assemblies (Asso) too. Crank was balanced, very smooth running now.

[bigbikerrick]

If you take your time, and remove material slowly and carefully, you should be able to get both rods to be  at least within 1 gram of each other. When I balanced the Gilardonis in my eldo, I was able to get the reciprocating parts to within 1/2 gram of each other. Like Charlie, I was lucky that both my rods weighed exactly the same.

[Testarossa]

After swapping parts around I realized that the first time I weighed these, the rods were mismatched with their lower shells. I did a little hand filing, fussed for an hour to get a reproducible method of weighing the rod ends, and came up with total weight difference of 0.1 gram, big ends differ by 0.5 and small ends by 0.7.  There's a .5 difference between my Gilardoni piston assemblies, so I can put the heavy piston on the light small end and I think I'll be fine.