Topic: Balancing of the crankshaft

[DresdaHonda]

Hello Racers

How to balancing of the crankshaft on a sohc ?
What is possible to do, by you self ? -and what has to be don by professionals
-I´m not talking about lighting the crank, just balancing...


Peter on a cb550

[MCRider]

Hello Racers

How to balancing of the crankshaft on a sohc ?
What is possible to do, by you self ? -and what has to be don by professionals
-I´m not talking about lighting the crank, just balancing...


Peter on a cb550

Balancing is usually done by spinning it to high RPMs, and strategic removal of material. Requires a pro, IMO. Click the APE banner at top of page.

Others can do it too.

PS: I see you are in Denmark. I'm sure there are places there that can do it.  Search Rob Voxonda, He probably knows.

[mlinder]

You need someone with the correct equipment to do it, unless you are capable of detecting fractions of grams difference on one side of a crank or the other.

[Jerry Rxman Griffin aka MuthaF'er]

From my understanding, the cranks are fairly well balanced to begin with. If you have it lightened it will also get balanced during the process. I had mine done by member Big Jay of APE here in the States. The info on it is: balanced for sustained operation to 17,000 rpm (don't I wish!) ; maximum tolerances in inch/ounces = 0.07 ; actual dynamic balance in inch/ounces = left 0.02 right 0.01.   

[lordmoonpie]

From my understanding, the cranks are fairly well balanced to begin with. If you have it lightened it will also get balanced during the process. I had mine done by member Big Jay of APE here in the States. The info on it is: balanced for sustained operation to 17,000 rpm (don't I wish!) ; maximum tolerances in inch/ounces = 0.07 ; actual dynamic balance in inch/ounces = left 0.02 right 0.01.   

Don't you believe it Jerry - they can be way off especially if you include attached rotors etc. I always get my race cranks balanced - brilliant service at Bassett Down Balancing here in the UK and it's not expensive. They have a website you can find on google if anyone is interested...

[Jerry Rxman Griffin aka MuthaF'er]

Good info. I haven't had the rotor done.

[a700guy]

does ape take into account balancing with the rotor and weight of your particular piston rod combo?

[MCRider]

does ape take into account balancing with the rotor and weight of your particular piston rod combo?

You should email them directly, but...my understanding is that with our 180 deg inline 4s, the piston and rod weights don't matter. they should be balanced to themselves, but independent of the crank.

As to the rotor yes it needs to be included so they can balance it too.

[Jerry Rxman Griffin aka MuthaF'er]

Good info. I haven't had the rotor done.

Don't know if Big jay gets into it that deep but not normally. If you got the cash send him a PM.

[a700guy]

Ahh, I will do that then, I was of the understanding that the mass of the big end of the rod came into play.

As you can tell I'm not a multi cylinder expert, the only other multi cylinder crank I have ever had balanced was in my dragster many moons ago, Reher Morrison did that crank and the needed the piston/rod combo to calculate bob weights they attached to the crank before spinning it up and stated if I ever made a change in rod brands or pistons and could not resolve them to be the same weight I would need to do it again.

Thanks for putting up with my endless questions.

[MCRider]

Ahh, I will do that then, I was of the understanding that the mass of the big end of the rod came into play.

As you can tell I'm not a multi cylinder expert, the only other multi cylinder crank I have ever had balanced was in my dragster many moons ago, Reher Morrison did that crank and the needed the piston/rod combo to calculate bob weights they attached to the crank before spinning it up and stated if I ever made a change in rod brands or pistons and could not resolve them to be the same weight I would need to do it again.

Thanks for putting up with my endless questions.

The mass does matter, its just that our 180 deg layout cancels it out. On a crank with throws at different intervals, like a Harley or a V8, it would matter and weights and calculations are made.

[a700guy]

gotcha

filing that one away under how not to look silly again..lol

[MRieck]

 The rotor can be balanced and should be if it is cut down.

[Big Jay]

There are two types of balance as could be related to a four cylinder crank.. Static and dynamic.  Static won't work on a crankshaft. You could have one end 50 grams heavy in one spot, and the other end 50 grams heavy 180 degrees opposite. This crank would be in perfect static balance.

But when you spun it up, it would act like two out of balance wheels connected by a common shaft.  Dynamic balancers measure the imbalance in what is referred to as an X plane thru the center of the crank. So with that you would correct both ends of the above crank, and it would then be both in static and dynamic balance, and not try to oscillate when spun up.

So you really can not do it your self. It is not like balancing a wheel on your bike.

You do not have to weigh the components and add bobweight like on a V8 or V6, etc. The inline four ( not big bang ) is 'self cancelling" . As long as all of your components weigh the same, the balance will still be good. That is why you can swap out stock pistons and rods for a 1000 kit and Carrillos and still have a balanced assembly.

As was pointed out above, we balance the cranks to an extremely tight tolerance, not so you can spin it to 14,000 plus, but to allow the builder to have a small leway in their component weights.

http://aperaceparts.com/mailers/crankmail.html

[Howell]

There are two types of balance as could be related to a four cylinder crank.. Static and dynamic.  Static won't work on a crankshaft. You could have one end 50 grams heavy in one spot, and the other end 50 grams heavy 180 degrees opposite. This crank would be in perfect static balance.

But when you spun it up, it would act like two out of balance wheels connected by a common shaft.  Dynamic balancers measure the imbalance in what is referred to as an X plane thru the center of the crank. So with that you would correct both ends of the above crank, and it would then be both in static and dynamic balance, and not try to oscillate when spun up.

So you really can not do it your self. It is not like balancing a wheel on your bike.

You do not have to weigh the components and add bobweight like on a V8 or V6, etc. The inline four ( not big bang ) is 'self cancelling" . As long as all of your components weigh the same, the balance will still be good. That is why you can swap out stock pistons and rods for a 1000 kit and Carrillos and still have a balanced assembly.

As was pointed out above, we balance the cranks to an extremely tight tolerance, not so you can spin it to 14,000 plus, but to allow the builder to have a small leway in their component weights.

http://aperaceparts.com/mailers/crankmail.html

The crank of our Cb500 racer is lightened and dynamic balanced.

[wannabridin]

so to the experts, if you've having your crank balanced, is it worth it to just send you the whole assembly, rods, pistons, rotor and all?  if you (Jay or Mike) balance everything together, then you should have a very smooth reciprocating assembly correct??

or would it just be a waste of time/money to send you everything at once like that...

[Sam Green Racing]

Yes Gee, it would be a waste of money, send your money to me, I have plenty of time to waste counting your money.

Sam.

[a700guy]

There are two types of balance as could be related to a four cylinder crank.. Static and dynamic.  Static won't work on a crankshaft. You could have one end 50 grams heavy in one spot, and the other end 50 grams heavy 180 degrees opposite. This crank would be in perfect static balance.

But when you spun it up, it would act like two out of balance wheels connected by a common shaft.  Dynamic balancers measure the imbalance in what is referred to as an X plane thru the center of the crank. So with that you would correct both ends of the above crank, and it would then be both in static and dynamic balance, and not try to oscillate when spun up.

So you really can not do it your self. It is not like balancing a wheel on your bike.

You do not have to weigh the components and add bobweight like on a V8 or V6, etc. The inline four ( not big bang ) is 'self cancelling" . As long as all of your components weigh the same, the balance will still be good. That is why you can swap out stock pistons and rods for a 1000 kit and Carrillos and still have a balanced assembly.

As was pointed out above, we balance the cranks to an extremely tight tolerance, not so you can spin it to 14,000 plus, but to allow the builder to have a small leway in their component weights.

http://aperaceparts.com/mailers/crankmail.html

The crank of our Cb500 racer is lightened and dynamic balanced.

That is one sexy crank!!!
The only guy who I have seen that takes that much off a 750 crank doesn't specialize in race motors like APE so I am a little leary to have him cut off that much.

[Big Jay]

so to the experts, if you've having your crank balanced, is it worth it to just send you the whole assembly, rods, pistons, rotor and all?  if you (Jay or Mike) balance everything together, then you should have a very smooth reciprocating assembly correct??

or would it just be a waste of time/money to send you everything at once like that...

Don't send anything but the crank.