Balance shafts in modern engines
Turbo Mini Forums

Was just wondering if any of you clever guys on here have worked with them or know how they work. I see a program on Discovery last week about a privateer building a one off motoGP bike. I was fasinated when it come to the stage where they were developing the engine which was a V4 with the most amazing induction system that went between the 3 cams and through the cam cover. They also showed this balance bar but I never thought much of it.
Then yesterday I was reading an article in Performance BMW about the new diesel engines BMW are making using balance bars and how a milestone has been made interms of engine smoothness. Then I also thought, Ive got a rotating bar going through my engine now which is doing nothing other than powering the oil pump now. Was just wondering if I could adapt a blank billet camshaft to work in the same way. Id have to get it to spin at the same speed as the crank so I'd also have to gear it down too.

It could be a load of bollox but it was only an idea while sitting in the bath.

ive rebuilt a toyota landcruiser engine which has 2 balance shafts in. there were lots of gears and timing marks it were a right ball ache.

your engine wont need it so dont worry about it. lol

no longer a series, but still 1.3 turbo.

Yeah your right. Was just wondering if it could make an improvment for not alot of money.

All the Mitsu Evo engines have them in. Balance Shafts that is. And most if not all Tuners throw them in the bin.

Si

I drill holes in everything..!

Oh right, well there must be a reason for them doing that so ill give it a miss then.

http://www.turbominis.co.uk/forums/index.php?p=vt&tid=177250

http://en.wikipedia.org/wiki/Balance_shaft

I reckon it would be pretty pointless after reading the wikipedia. Sounds like ill loose power and have a less responsive engine.

Can't beleive how good that wikipedia is either. Its got everything imaginable on there.

always cut the balance shafts out hwne rebuilding evo engines. waste of space and tbo make neglegabel difference anyways as when proerply ballanced its a nice revvy smooth engine anyways. could see the need for them on "odd" engines like inline 3 cylinder efforts.

turbo 16v k-series 11.9@118.9 :)

Denis O'Brien.

That just the point, those who remove them seem to think that good balancing will replace them, when it never ever will.

A 4cylinder engine produces harmonics that cannot be corrected by balancing the components, thats why crank dampers and balance shafts are fitted.

Removing a balance shaft is the same as removing the crank damper on a 1275 A series. No noticeble difference is seen , but the fatigue life of the crank is some what reduced, to what level, i dont know. It wouldnt be there if there wasnt a reason for it.

On the other hand, if you have heavily modified the rotating and reciprocating mass, then the standard balance shaft is useless.

Edited by Sprocket on 12th Oct, 2008.

My SAAB has balancing shafts and I must say its the smoothest revving 4 cylinder engine I have ever driven...

website:- http://www.terryhunt.co.uk

turbo 16v k-series 11.9@118.9 :)

Denis O'Brien.

THe balance shafts are there to remove all the harmonics of a different order of what can be removed by simply balancing of the crankshaft. To remove the other order harmonics the balance shafts need to run on different rpms. (typically, half, double or 4 times the speed). This is written about in depth in Heywoods book on internal combustion engines.

The dampers do not do a very good job of this as they spin at the same speed as the crank, thus balance shafts are used.

Affects vibrations in the engine as a whole,yes, that's ythere job, still don't think removing balance shafts will affect the fatigue life of the crank.

turbo 16v k-series 11.9@118.9 :)

Denis O'Brien.