Balance Shaft Discussion
Evolving Member
Joined: Dec 2015
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From: HWY 9
Evolving Member
Joined: Sep 2017
Posts: 135
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From: EvoNation
Guys why you are making it so complicated. It is very clear to me. Drag racers do not care for any kind of vibration, their engine was built for 1/4mile passes and this is it! Also highly modified seem to remove them either to free some ponnies or if they spin their motors to 9k which the balance shaft will actually spin to 18k!!! Daily driven cars seem to keep them, as its removal benefit are not totally worth it. It all comes down to what your goals are and what is the purpose of your build.
Evolved Member
Joined: Mar 2008
Posts: 2,110
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From: Croatia
My biggest gripe with removing the balance shafts is that you're removing a component designed to minimize vibration. Vibration causes accelerated wear on components. How much is up to debate, but if you can feel the NVH from removing the shafts, your components can too. Comparing to solid engine mounts is an unfair comparison, as we're talking about minimizing internal engine vibration, not just minimizing the transfer of harmonics to the chassis(the whole point of rubber engine mounts as opposed to solid ones).
Evolving Member
Joined: Sep 2017
Posts: 135
Likes: 5
From: EvoNation
Also, car manufacturers always build their engines with reliability being their main goal. They do not care much about the rotational weight. 4G63's were built so many years ago and their 280hp is minimal to what this engine was proven to produce. What i am trying to say is that for reliability, mitsu engineers kept the balance shafts. But we must keep in mind that, what we are developing our engines (from 280hp to i.e 800whp and 7.5k rev to 9k) is so drastical change and deleting them is very reasonable choice. I personally chose what i believe is the best of both worlds
Even the engineers who design balance shafts say they are for NVH purposes.
https://www.evolutionm.net/forums/ev...ft-belt-6.html
There are TONS of 4 cylinder engines that don't use balance shaft systems and you don't hear of them chewing through bearings because they vibrate so badly. And if you think that a 4 cylinder engine without balance shafts has a lot of vibrations, you should see the kind of vibrations an odd firing V10 has. I've talked to engineers who've had viper engines rip motor mounts out of the walls they were mounted to because they were vibrating so badly.
https://www.evolutionm.net/forums/ev...ft-belt-6.html
I have a good amount of experience developing balance shaft systems for OEMs. I've literally reviewed hundreds of hours of run data on engines, talked about this same stuff with other engineers who design these systems for a living, seen results first hand. Removing balance shafts will cause no damage to an engine. They are only for NVH purposes.
There are TONS of 4 cylinder engines that don't use balance shaft systems and you don't hear of them chewing through bearings because they vibrate so badly. And if you think that a 4 cylinder engine without balance shafts has a lot of vibrations, you should see the kind of vibrations an odd firing V10 has. I've talked to engineers who've had viper engines rip motor mounts out of the walls they were mounted to because they were vibrating so badly.
Guys why you are making it so complicated. It is very clear to me. Drag racers do not care for any kind of vibration, their engine was built for 1/4mile passes and this is it! Also highly modified seem to remove them either to free some ponnies or if they spin their motors to 9k which the balance shaft will actually spin to 18k!!! Daily driven cars seem to keep them, as its removal benefit are not totally worth it. It all comes down to what your goals are and what is the purpose of your build.
Also, car manufacturers always build their engines with reliability being their main goal. They do not care much about the rotational weight. 4G63's were built so many years ago and their 280hp is minimal to what this engine was proven to produce. What i am trying to say is that for reliability, mitsu engineers kept the balance shafts. But we must keep in mind that, what we are developing our engines (from 280hp to i.e 800whp and 7.5k rev to 9k) is so drastical change and deleting them is very reasonable choice. I personally chose what i believe is the best of both worlds
Thread Starter
Joined: Jul 2012
Posts: 3,294
Likes: 197
From: California
Guys why you are making it so complicated. It is very clear to me. Drag racers do not care for any kind of vibration, their engine was built for 1/4mile passes and this is it! Also highly modified seem to remove them either to free some ponnies or if they spin their motors to 9k which the balance shaft will actually spin to 18k!!! Daily driven cars seem to keep them, as its removal benefit are not totally worth it. It all comes down to what your goals are and what is the purpose of your build.
BS uses a little energy to cancel out internal forces inside the block metal between journal bearings of BS and crankshaft. It creates forces in the center of the bock metal at the inner journal bearing of the BS. The lateral front to back forces cancels each other out from front center journal bearing to rear center journal bearing of each BS.
The up & down forces cancels or eliminates the combined forces of all the crankshaft journal bearings. The crankshaft journal bearings changes direction of forces because of the motion of pistons every 90° crankshaft rotation. I still believe that BS cancels out or reduces (from changing to bigger stroke) the up/down resultant forces of all 4 piston movement by tightening up the crank journals to bearing clearances so the bearings are tight when needed (to allow rotation of crank).
As long as oil does what it's supposed to, they should provide the lubrication and the thin oil pressure between the main bearings and crank journals will help cushion the vertical forces of the crankshaft (caused by piston motions). Crankshaft journals do make contact with bearings once the oil is squeezed out (you can see this in teardown). Over time, the clearance at these points will increase and oil pressure can drop if oil pump volume is insufficient to sustain the larger clearance. This is why it is good practice to refresh race engines often. So BS aren't needed in race engines. If you don't refresh often, then watch your oil pressure to know when you have to rebuild before oil starvation destroys the motor.
One more thing, the higher you rev your engine, the BS spins twice as fast to create higher forces. So at 9,000 RPM, BS is spinning at 18,000 RPM to create more forces to resist the crankshaft forces (which are also higher). It just helps the bearings work better. The weakest point is the BS belt. But don't worry, that isn't spinning at 18,000 RPM. BS is only a tiny weight that is slightly off centered, so it's not as scary as pistons going up and fown at 9,000 RPM.
Last edited by 2006EvoIXer; Apr 6, 2019 at 08:06 AM.
EvoM Community Team Leader
Joined: Aug 2005
Posts: 5,690
Likes: 708
From: West Coast
I must of said this a few times now, you can't cancel forces, you are simply masking the vibrations caused by those forces. The crank still strains under the imbalance, and so does the balance shaft, they just strain in exactly the opposite way. Their bearings are still feeling that imbalance. The opposite waves cancel each other out when they meet, but they are both still being generated by the engine.
Last edited by Biggiesacks; Apr 6, 2019 at 08:11 AM.
I must of said this a few times now, you can't cancel forces, you are simply masking the vibrations caused by those forces. The crank still strains under the imbalance, and so does the balance shaft, they just strain in exactly the opposite way. Their bearings are still feeling that imbalance.
Thread Starter
Joined: Jul 2012
Posts: 3,294
Likes: 197
From: California
I must of said this a few times now, you can't cancel forces, you are simply masking the vibrations caused by those forces. The crank still strains under the imbalance, and so does the balance shaft, they just strain in exactly the opposite way. Their bearings are still feeling that imbalance. The opposite waves cancel each other out when they meet, but they are both still being generated by the engine.
We can discuss in a separate group the technicalities to avoid confusing everyone else.
And yes, I agree with what you're saying.
Last edited by 2006EvoIXer; Apr 6, 2019 at 08:50 AM.
Thread Starter
Joined: Jul 2012
Posts: 3,294
Likes: 197
From: California
Thread Starter
Joined: Jul 2012
Posts: 3,294
Likes: 197
From: California
Why are there so many engines running without BS and not experience problems? These are the two reasons I can think of:
1) oil is sufficient to cushion the clearance between bearings crank journals
2) bearing and crank journal contact patch is big enough to hold the forces and the clearance is still within tolerance of the oil properties. This can still provide a very long service life (think of bearings like properly broken in brake pads where each hard acceleration makes a little contact like braking).
1) oil is sufficient to cushion the clearance between bearings crank journals
2) bearing and crank journal contact patch is big enough to hold the forces and the clearance is still within tolerance of the oil properties. This can still provide a very long service life (think of bearings like properly broken in brake pads where each hard acceleration makes a little contact like braking).
Uncovered some info i found interesting:
- The Porsche 944 is a very large displacement 4 cyl & uses the BS technology (their forum topics struggle w/the BS deletion issue as well)
- Porsche licensed their BS design directly from good O'l Mitsubishi
- The BS technology was developed by: Frederick Lanchester (British Engineer Circa 1904)
Evolved Member
Joined: Mar 2008
Posts: 2,110
Likes: 320
From: Croatia
You are just plain wrong. Bs does nothing for journal bearings.. it just makes the block shake less.. it has zero effect on bearing life.
Second... balance belts do break. I just found one that broke after 5 years.... and also managed to buy a g64 engine cheaply that broke its belt abd that was from a gallant daily driver....
Fact is bs does nothing really.. you can hardly feel when they are off.
Second... balance belts do break. I just found one that broke after 5 years.... and also managed to buy a g64 engine cheaply that broke its belt abd that was from a gallant daily driver....
Fact is bs does nothing really.. you can hardly feel when they are off.
You hit the nail on the head. This is what it boils down to.
BS uses a little energy to cancel out internal forces inside the block metal between journal bearings of BS and crankshaft. It creates forces in the center of the bock metal at the inner journal bearing of the BS. The lateral front to back forces cancels each other out from front center journal bearing to rear center journal bearing of each BS.
The up & down forces cancels or eliminates the combined forces of all the crankshaft journal bearings. The crankshaft journal bearings changes direction of forces because of the motion of pistons every 90° crankshaft rotation. I still believe that BS cancels out or reduces (from changing to bigger stroke) the up/down resultant forces of all 4 piston movement by tightening up the crank journals to bearing clearances so the bearings are tight when needed (to allow rotation of crank).
As long as oil does what it's supposed to, they should provide the lubrication and the thin oil pressure between the main bearings and crank journals will help cushion the vertical forces of the crankshaft (caused by piston motions). Crankshaft journals do make contact with bearings once the oil is squeezed out (you can see this in teardown). Over time, the clearance at these points will increase and oil pressure can drop if oil pump volume is insufficient to sustain the larger clearance. This is why it is good practice to refresh race engines often. So BS aren't needed in race engines. If you don't refresh often, then watch your oil pressure to know when you have to rebuild before oil starvation destroys the motor.
One more thing, the higher you rev your engine, the BS spins twice as fast to create higher forces. So at 9,000 RPM, BS is spinning at 18,000 RPM to create more forces to resist the crankshaft forces (which are also higher). It just helps the bearings work better. The weakest point is the BS belt. But don't worry, that isn't spinning at 18,000 RPM. BS is only a tiny weight that is slightly off centered, so it's not as scary as pistons going up and fown at 9,000 RPM.
BS uses a little energy to cancel out internal forces inside the block metal between journal bearings of BS and crankshaft. It creates forces in the center of the bock metal at the inner journal bearing of the BS. The lateral front to back forces cancels each other out from front center journal bearing to rear center journal bearing of each BS.
The up & down forces cancels or eliminates the combined forces of all the crankshaft journal bearings. The crankshaft journal bearings changes direction of forces because of the motion of pistons every 90° crankshaft rotation. I still believe that BS cancels out or reduces (from changing to bigger stroke) the up/down resultant forces of all 4 piston movement by tightening up the crank journals to bearing clearances so the bearings are tight when needed (to allow rotation of crank).
As long as oil does what it's supposed to, they should provide the lubrication and the thin oil pressure between the main bearings and crank journals will help cushion the vertical forces of the crankshaft (caused by piston motions). Crankshaft journals do make contact with bearings once the oil is squeezed out (you can see this in teardown). Over time, the clearance at these points will increase and oil pressure can drop if oil pump volume is insufficient to sustain the larger clearance. This is why it is good practice to refresh race engines often. So BS aren't needed in race engines. If you don't refresh often, then watch your oil pressure to know when you have to rebuild before oil starvation destroys the motor.
One more thing, the higher you rev your engine, the BS spins twice as fast to create higher forces. So at 9,000 RPM, BS is spinning at 18,000 RPM to create more forces to resist the crankshaft forces (which are also higher). It just helps the bearings work better. The weakest point is the BS belt. But don't worry, that isn't spinning at 18,000 RPM. BS is only a tiny weight that is slightly off centered, so it's not as scary as pistons going up and fown at 9,000 RPM.
