Hitchcocks Forum

Hi Everybody!
Can anybody tell me the standard balancing weight that´s used for the Indian-made 10,5kg 500cc crankshafts and/or the weight of a complete 500cc standard piston?
Thanks and cheerio,
Connie1959

Hi..Why not weigh the piston complete with circlips and rings and gudgeon pin? Then weigh the small end eye of the con rod in a horizontal position on electronic scales. Add the two together and multiply by the balance factor. The combined weight is the weight attached to the small end eye and balanced out on the flywheels to leave the crankshaft neutrally balanced. Some use an arbitary 66% but I have read the exact figure somewhere and I think it was something like 58%. Whatever the BF it is very easy to do. I'll try to find out the correct BF, would like to know myself...

Hi Les,
thanks for your help and reply.
Unfortunately do I have no loose 500cc piston which I could weigh. Any idea of the weight of a 500cc standard piston?
I been told that the original production-BF shall be 70% but, that the engine runs more comfortable at the same BF as the BSA B44 at 52%.
Lookin´ foreward...

Connie,
OEM piston with gudgeon, circlips and rings weighs 534 grams

Great! Thanks a lot so far!

Hello again Con...don't forget to make sure the crank assembly is balanced symetrically about the crank-pin BEFORE you start to adjust the balance factor in.
With no weight attached to the big end eye, the crank assembly should come to a stop on the straight edges with the crank pin absolutely vertical at the top most position. Drill equal size holes on each crankweb at 90 degrees to the pin on the heavy side to achieve perfect static symetrical balance. Then you can start balancing with the balance factor weight attached making sure same amounts are taken off each crankweb in exactly the same relative positions as close to the pin as you can and also symetrical either side of the pin IF a position in line with the pin is not possible. BTW...I've managed to find about 10 different BF's for the Bullet but not one is the same...still can't find the source of the original official figure that I read not too long ago.

HI Connie, 1959, Les H, and Norm.
May I join your debate on crankshaft/ piston ballancing.
I have a similer problem, in that I have a 350cc RE crankshaft and a 500 top end.
The 500 cc piston that I have weighs in at 493 grms,but to get anywhere near equilibrium
with the crank assembly I have to find a lighter piston and then balance the assembly.
While the crank/conrod was on my ballancing rig, I added weights to the small end of the conrod
and found that I needed 230 grms to achieve neutral balance.
Now I am sure that I wont find a piston of that weight, so any ideas on where I can purchase a piston that is lighter than 493 grms
to fit 84mm bore (nominal) and then balance the assembly.

cheers
joppalad

Hi Joppalad. You don't seem to be accounting for the balance factor. Your piston weighs 500g......The con rod eye in horizontal position weighs....just guessing at 100g........add together = 600g..... then multiply by balance factor...(say 60%) = 360g.......... You have a balance with 230g........ so you need to drill the crank flywheels to remove the extra 130g.........These are rounded figures and I have used an arbitary balance factor figure.

Just to add...the drillings will be centered around the big end eye and the drillings will be symetricl and equal on both flywheels..As I said earlier to do the static balance first to get the the crank symetrically balanced. ..just to explain, by REMOVING the 130g of the flywheels in my example, you can see that an EXTRA 130g will now need to be ADDED to the balancing weight on the con rod eye to achieve the new balance.

Just one more thing Joppalad. If you have the original 350 piston you could weigh it and the extra weight of the 500cc piston is the amount that needs to be removed from the flywheels. This way keeps the balance factor the same as it was.