cranks again ..sorry!

Anyone know the balance weight that the stock pistons ,pins ,rings and small end of the rods is? how would i weigh the rod ends, how much of the rod end is added?
Never could figure that bit, how far down the rod is weighed?

The theory is that you have the rod perfectly horizontal, and weigh under each end.
That is the distribution of weights apportioned to rotating and reciprocating.

In practice, this probably means that no two "52%" are actually the same...

As Rohan pointed out, the rod is supported on one end, such that an imaginary horizontal line exists between the centers of the large and small ends, and the opposite end is weighed on a balance or scale. The link below shows one means of fixturing the rod for weighing.

http://www.youtube.com/watch?v=QLpiF0E0EJU

You don't need a fancy fixture to perform a simple one time weighing, as you can suspend the unweighed rod end with string, wire, fish line, a what ever you want inserted through the rod large or small end, so long as the rod is ultimately oriented "horizontal". The fish line/wire/string method is convenient as it allows you to quickly make vertical adjustments to orient the connecting rod horizontally. You can check your work by weighing both the small and large ends and making sure that the sum of the individual ends equals the total rod weight.

I didn't balance the rods in my 850 because the revs don't really get high enough to matter. I built a T250 Suzuki which ran methanol and I balanced the rods end for end. I didn't use the method shown in the video. I use a laboratory balance with a V shaped support in front of the pan and a piece of glass rod on the pan. I laid the rod on it's side and weighed each end after placing each rod in the same position on the balance and support. The V and the glass rod go under the bearing centres as you weigh each end. I found the little end of one rod was much heavier than that of the other. If you could inspect the Japanese rods as you buy them you would see the differences. I ground the weight off the heavier little end and then ground the rods all over. Japanese rods are shot peened and copper plated to remove stress raisers. The bike was very vibration free and after I sold it won 28 historic races and 5 championships - never broke a rod. I would not tamper with an aluminium Norton rod in that way. When I balanced the 850 I simply followed Phil Irving's method in Tuning for speed and weighed the pistons, gudgeons, clips and rings. The balance factor is not critical, however it must suit the operating rev range so the crank doesn't destroy the bearings and cases. (Rohan will argue about that).

If you didn't even know that most of the rods weight is considered as rotating weight,
then its probably best to take any 'advice' you give on the matter of crank balance with a grain of salt...

Somehow we think that out-of-balance forces in a Commando maybe be a bit more than in a wee blue smoke,
so again that grain of salt....

And it has always been emphasised here to chase a suitable crank balance factor to suit the vibration charateristics of the chassis being employed,
perhaps you have learnt something after all.

So are you saying forget the rod weight..just the piston assembly?

Rohan said:

If you didn't even know that most of the rods weight is considered as rotating weight,
then its probably best to take any 'advice' you give on the matter of crank balance with a grain of salt...

Somehow we think that out-of-balance forces in a Commando maybe be a bit more than in a wee blue smoke,
so again that grain of salt....

And it has always been emphasised here to chase a suitable crank balance factor to suit the vibration charateristics of the chassis being employed,
perhaps you have learnt something after all.

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My reply was aimed squarely at the half-nonsense Alan usually posts.
If you want to believe any of what he says, thats up to you.
I'd stick to tried and tested and proven methods....

Gen. G.I. Brassbottom: It's either turkeys gobbling or Congress is back in session.

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Rods dead horizontal , on your local post office electronic balance . Or on a hung thing .

First things CRACK TEST the CRANK . belting it to see if it rings is likely adequate -

Dynamic crank balance - unless he was drunk , the factorylikely did a good job , for road use - though could be refined .

One watches where one removes metal on rods - not load bearing areas .

Right - Matching ( side to side / pair ing Weights , IS important .

Rohan no doubt will supply us with a list of the required balance factors for Norton Engines ( all ) in forign ( to make ) chassis ( all )

“I told you not to mention that.”
~ Roger Ramjet on unmentionables

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