Posted By: Anonymous
Balancer shaft removal - 15/11/2016 09:11
Hi there,
I wanted to react to Hoops82 post and not pollute the other one (I hope it's the right way to do this).
I think I get the hole idea of the post (I still lack some English...).
Just to be precise : balance shaft help reducing engine vibration/shacking but they do not reduce stresses on internals components (crank/rods/pistons). The dampening is done on surfaces far away from crank bearing.
Resulting moments and efforts that the engine puts on the chassis are reduced but internals forces (and associated stresses) on engine internal parts are not modified.
Also, the original balance shaft belt is limited to 12000rpm (maybe belt's manufacturers have improved it's resistance from first models) and considering that stock engine go to 6000rpm and the speed ratio balancer shaft/crankshaft is about 2:1, there is a high risk the belt can break even on a stock engine.
-> Tuning our lampredi usually need the engine to rev higher (I ran 7000rpm on stock engine internals) so this is a reliability mod to delete this belt with no downsides on engine internal reliability (unless you consider that engine's vibration can have negative effects on internals).
Regards
I wanted to react to Hoops82 post and not pollute the other one (I hope it's the right way to do this).
Originally Posted By: Hoops82
Good info, thanks Honza. Most helpful for the thread.
On the subject of balance shaft removal, that is not the purpose of this thread and there are many texts and papers on the subject.
I would just like have a quick rant
because, for me, balance shaft removal is a very lazy un-engineered and rather agricultural solution to a fairly simple desire to change other components.
I can assure you that balance shafts are neither unique to the lampredi, nor only there for the sales man on the showroom floor to talk about smoothness of the engine. They are found in all engine configurations from twins through straight 6's to V8's as well as gas turbines but are prevalent in equal number in line designs. They still exist in the modern age but are less prevalent owing to more controlled combustion and feedback processes rather than a question of reciprocating component balance. In fact, 2nd order harmonics have little to nothing to do with components being out of balance and almost everything to do with the crank shaft big end journal configuration choice, i.e. firing order and combustion chamber design (combustion harmonics).
Their (balance shaft) purpose is to reduce, dampen and eliminate torsional and 2nd order harmonics (in the case of equal number engines) particularly in the horizontal plane of the engine perpendicular to the axial plane of the crank shaft.
Without going into too much detail, it is a mathematical fact that they lengthen component life particularly of the con rods by reducing the eigenvector stresses associated with lateral loading and therfore lowering the damage ratio per cycle and lengthen the fatigue life. It is fairly complex to model involving fourier transforms of eigenvectors to accurately place dynamic loading from an ever shifting center of mass due to precession of virtual axis.
No doubt, many people remove them and get on fine. But having run simulations and designs involving balance shafts (not for our beloved Lampredi i should say), I will never be convinced by anything other than a model showing their in-effectiveness. (happy to concede if someone will send me a fatigue cycle calculation involving the specs of the lampredi)
Obviously, as we modify our engines we must make design compromises to the life of the engine for increased performance. However, in the case of balance shafts, the gain is effectively Zero for a significant increase in risk factor. I would liken it to grinding off the paintwork of your car and taking the rapid corrosion that would result in account for a saving of a few grams in weight.
I do concede the point about balance shaft snapping being a risk though KJ, have experienced that on a recent Alfa type939
Anyway, Rant over. The point of the thread is to help us find a cheap and cost effective solution to increasing the cam belt strength whilst maintaining the original reciprocating mass engine design. For those who don't wish to remove the belts (we may be few!).
A thread on balance shaft removal merits could be started separately if people wish to discuss that.
On the subject of balance shaft removal, that is not the purpose of this thread and there are many texts and papers on the subject.
I would just like have a quick rant
because, for me, balance shaft removal is a very lazy un-engineered and rather agricultural solution to a fairly simple desire to change other components.I can assure you that balance shafts are neither unique to the lampredi, nor only there for the sales man on the showroom floor to talk about smoothness of the engine. They are found in all engine configurations from twins through straight 6's to V8's as well as gas turbines but are prevalent in equal number in line designs. They still exist in the modern age but are less prevalent owing to more controlled combustion and feedback processes rather than a question of reciprocating component balance. In fact, 2nd order harmonics have little to nothing to do with components being out of balance and almost everything to do with the crank shaft big end journal configuration choice, i.e. firing order and combustion chamber design (combustion harmonics).
Their (balance shaft) purpose is to reduce, dampen and eliminate torsional and 2nd order harmonics (in the case of equal number engines) particularly in the horizontal plane of the engine perpendicular to the axial plane of the crank shaft.
Without going into too much detail, it is a mathematical fact that they lengthen component life particularly of the con rods by reducing the eigenvector stresses associated with lateral loading and therfore lowering the damage ratio per cycle and lengthen the fatigue life. It is fairly complex to model involving fourier transforms of eigenvectors to accurately place dynamic loading from an ever shifting center of mass due to precession of virtual axis.
No doubt, many people remove them and get on fine. But having run simulations and designs involving balance shafts (not for our beloved Lampredi i should say), I will never be convinced by anything other than a model showing their in-effectiveness. (happy to concede if someone will send me a fatigue cycle calculation involving the specs of the lampredi)
Obviously, as we modify our engines we must make design compromises to the life of the engine for increased performance. However, in the case of balance shafts, the gain is effectively Zero for a significant increase in risk factor. I would liken it to grinding off the paintwork of your car and taking the rapid corrosion that would result in account for a saving of a few grams in weight.
I do concede the point about balance shaft snapping being a risk though KJ, have experienced that on a recent Alfa type939
Anyway, Rant over. The point of the thread is to help us find a cheap and cost effective solution to increasing the cam belt strength whilst maintaining the original reciprocating mass engine design. For those who don't wish to remove the belts (we may be few!).
A thread on balance shaft removal merits could be started separately if people wish to discuss that.
I think I get the hole idea of the post (I still lack some English...).
Just to be precise : balance shaft help reducing engine vibration/shacking but they do not reduce stresses on internals components (crank/rods/pistons). The dampening is done on surfaces far away from crank bearing.
Resulting moments and efforts that the engine puts on the chassis are reduced but internals forces (and associated stresses) on engine internal parts are not modified.
Also, the original balance shaft belt is limited to 12000rpm (maybe belt's manufacturers have improved it's resistance from first models) and considering that stock engine go to 6000rpm and the speed ratio balancer shaft/crankshaft is about 2:1, there is a high risk the belt can break even on a stock engine.
-> Tuning our lampredi usually need the engine to rev higher (I ran 7000rpm on stock engine internals) so this is a reliability mod to delete this belt with no downsides on engine internal reliability (unless you consider that engine's vibration can have negative effects on internals).
Regards