Balance factor for 500cc

Hi Bernard,

If it was running well with the old pistons, i would weight the new / old pistons to find the difference and then remove the weight from the crank. Generally this is done by drilling holes opposite the counter weight as per picture attached. Below is a table showing what the weight is by drill size per 1" of depth.

1" depth = the drill sizes to weight are:

Hole Dia 1/2" 7/16 3/8 5/16 1/4

Castiron = 0.880.680.500.350.23 ounces

Any questions i can be contacted @ nortones2@internode.on.net

Cheers

Steve

Previously wrote:

hi

What should be the crankshaft balancing factor to get the sweethest at 4500 to 5000 rpm range for a 500cc Dominator?

Was using hepolite pistons now worn out and bike was vibration free at 4000 rpm but now i m fitting gpm pstons which are heavier and would like to either remove some weight of the pistons but afraid it will be a lot of aluminium to shave or rebalance the crankshaft ,hence this request

thanks ;bernard

Hi bernard,

I am a new member to the forum but not to norton twins. Use your old pistons to work out the balance factor you had, and use that if you like it. Weigh pistons , pins, small ends and big ends recalulate weights, and rebalance.

I have built a number of 500 twins for road and racing use, plus 500 short strokes and a 550 that is still knocking about here in Canada and have found 62% fairly good on the road and 82.5 on the track.

A good place to save wt on heavier pistons is by grinding out the pin ends, with a tapered stone if your pistons are not to far apart followed by polishing and shot peening for insurance. I would not taper in so far that you thin the area where pin, rod and piston meet.

Rgards Ian

Regards Ian

Hi Bernard

I don't wish to spoil you fun but ...........the last thing I would ever do with GPM pistons is to try and reduce their weight by shaving metaloff them.

Unfortunately, the first generation of theseitems did not have a particlularly good reputation for durability/reliability andgot a bad name for being very heavy, distorting badly and having ring sets thatwere not marked with 'top'.

The latestversions of these pistons seem to be better. The rings are now marked but sometimes come already fitted onto the piston upside down. Check them before re-assembly an engine. The pistons do now seem a little better in quality and don't seize so easily but.................. they are still very chunky and generally up to 30% heavier than the items they are replacing.

Which really throws the balance of the engine out by quitea long way.

I would recommend that the crankshaft is re-balanced by a professional/expert in this kind of work. Make sure that it is oil filled when balanced.

John Hudson said that all the twins, built at Bracebridge,had cranks balanced to 70%. But this was probably dry.

Hi Bernard. I was talking to Les Emery of Norvil only about a week ago on the same subject. He said the balance factor should be 84% WET (Oil) This was for a standard engine.

Les