Crankshaft balance weights

[Lawrie]

I'm having a new crank balanced at the local machine shop.
I see for the bob weight they have two alloy blocks witch clamps over the rod journal by threaded rod and the weight is made up using nuts and washers to get the weight right, would not a round bob weight be better,at the correct weight of corse.
Lawrie

[34PKUP]

Originally Posted by Lawrie

I'm having a new crank balanced at the local machine shop.
I see for the bob weight they have two alloy blocks witch clamps over the rod journal by threaded rod and the weight is made up using nuts and washers to get the weight right, would not a round bob weight be better,at the correct weight of corse.
Lawrie

Are you saying that the way they are doing it does not work?

[Mart]

As long as the centre of gravity of the bob weight assembly is on the centre of the rod journal the shape does not matter. They're normally Vee'd where it clamps on so it can fit any size journal. The washers and nuts must be equal on both sides of each bob weight assembly.

[JWL]

If the total weight is centered on the crank pin balancing should be accomplished. Usually the separate halves are weighed to within a gram before final positioning.

[KiWinUS]

Lawrie that’s how the Stewart Warner balancer components come. And standard procedure I believe with the S/W balancer.

[Lawrie]

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Thanks for the info, I was going to machine up some weights, which would be a big job,
So I will take the crank to the machine shop.
I have worked out the bob weight weight, so that will save some labour at the shop.
Lawrie

[Frank Miller]

There are a lot of videos on youtube about balancing crankshafts and what not. Look up a few to familiarize yourself. You may not be balancing the engine but you will have a good understanding when your machinist needs to explain something to you.

[JSeery]

Some examples.

[Pete]

Originally Posted by Lawrie

I'm having a new crank balanced at the local machine shop.
I see for the bob weight they have two alloy blocks witch clamps over the rod journal by threaded rod and the weight is made up using nuts and washers to get the weight right, would not a round bob weight be better,at the correct weight of course.
Lawrie

Of course, because they are more pleasing to look at..lol
Nobody likes to look at a piece of steel with a bunch of red-bolt, globs of washers and pieces of brass attached. When we bought the balancer we turned all of our bob weights out of bronze bar stock and use tapped, counterbored holes to put the adjustment washers in. The weights are crankshaft specific and since we only do a few types of engines, it works for us. There are good reasons for doing it this way when you are looking for that elusive 1/10 of a second per lap.
The actual weight of the bob weights is not absolutely critical to the gram on a V8 because you are balancing to 50% normally, BUT, the bob weights ABSOLUTELY have to all be the same weight very close. This affects DYNAMIC balance and that affects torsional vibration and that breaks cranks.
On race engines, many are over balanced (heavier than 50%) hence, if the calculated bob weight is off a few grams, it will have minimal to no effect.

The weights as pictured previously work fine. Don't sweat it.