balanced crank? do the rods need doing with it???

Post by **Coops** » Tue Feb 27, 2007 7:27 pm

i have a balanced crank here,
im looking at buying some balanced rods and pistons (stock 3.9 with valve reliefs) from DJE on ebay
will i need to get it all balanced together the rods pistons and crank?? if so how do they do it?

or is it ok to build into the engine as they are ????

ian.stewart · Post by **ian.stewart** » Tue Feb 27, 2007 7:52 pm

Static ballancing of the rods should be more than adequate, and if they are ballanced correctly there will be no adverse effects, but you should also get the pistons done as well

Post by **Coops** » Tue Feb 27, 2007 7:54 pm

the rods are balanced to +/- 1 gram
and the pistons are balanced +/- 1 gram

Post by **Rossco** » Tue Feb 27, 2007 10:03 pm

The balancer will need to know the weight of each rod and piston combo

Post by **Coops** » Tue Feb 27, 2007 10:06 pm

Rossco wrote:The balancer will need to know the weight of each rod and piston combo

Hi allan,
so i need to get it all balanced then???
the rods and pistons have been done by DJE
the crank by v8 developments

Post by **katanaman** » Tue Feb 27, 2007 10:08 pm

depends what the crank was balanced to. If it was balanced to lightend pistons and rods the balance will be out. Same if the pistons and rods were heavier I.E it was balanced for larger bore pistons

Post by **Coops** » Tue Feb 27, 2007 10:15 pm

just when i thought i was on a winner for once, its starts sounding expensive and grief again

ihatesissycars · Post by **ihatesissycars** » Tue Feb 27, 2007 10:16 pm

Balancing is only about £150 with real steel.

How much has the crank had removed from it? Is it covered in drillings and grinding marks?

Post by **Coops** » Tue Feb 27, 2007 10:24 pm

Balancing is only about £150 with real steel.

glad you said only Gav

ihatesissycars · Post by **ihatesissycars** » Tue Feb 27, 2007 10:27 pm

Do you have the original pistons and rods that crank was balanced with?

Post by **Coops** » Tue Feb 27, 2007 10:32 pm

not any more no mate

ihatesissycars · Post by **ihatesissycars** » Tue Feb 27, 2007 10:33 pm

bugger, you can wieght match new components to old ones that were in the original balance.

Plan B then. . . .

Boosted LS1 · Post by **Boosted LS1** » Wed Feb 28, 2007 11:37 pm

I do this. I weight the rods end to end and the pistons to, plus the shells and rings etc. This establishes the reciprocating and rotating masses. Without this information the crank will be out of balance for your combo, period. You'd probably have better odds with the lottery

That said, people do get away with unbalanced cranks but balanced items are soooo smooth.

Boosted.

kiwicar · Post by **kiwicar** » Thu Mar 01, 2007 9:31 am

Hi can I ask an extra question on this please?
I have just bought a ballanced bottom end kit from the states the, 7 rods are within +/- .3 grams but one rod is 1.5 grams lighter than the average. With the pistons and pins I can get them (by putting lightest pin with heaviest piston) to +/- .25 gramms of average, or I can get rod /piston /pin combinations that get to within +/- .7 grams, but this means making up a heavy piston/pin combination.
How should I combine them?
Should I bring all the rods to closer ballance with each other (they are at the moment all shot peaned so I would have to get any areas I lightened re done, also it is not obvious where to take material off). The other aproach might be to add wieght to the light rod in the form of a washer under each rod bolt but might this lead to the rod bolts comming undone during use?
Am I just being too fussy as the rods pistons pins are in pairs them I can get the weight on each big end to much closer range ??
thoughts and Ideas please.

Mike

Boosted LS1 · Post by **Boosted LS1** » Thu Mar 01, 2007 10:55 am

Hi Mike, you're as fussy as me

The specs are quite good but could be bettered. Are you able to weigh the rods end to end to find out where the lost weight is? If it's on the little end then you could lighten the other rods by shaving a tad off the side of the l/e or you could trim a bit from inside the piston skirts to reduce the reciprocating masses. If it's the b/e then remove some from the thickest part of the caps.

Another possibility is to add mass to the l/e. I once saw somebody bond something into the pin. It seemed to work well enough. Think it was a very thin shim with a big surface area.

Boosted.