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Thats one way to think of it. But there are also other possibilities that make sense. Just because a part exists on the car doesnt mean it is because its a necessity for longevity. Example EGR, EVAP canister, catalytic converter, CAM profile for MPG/smooth idle and not necessarily best power, possibly even balance shafts etc... They add certain parts and designs to pass emissions laws, attract majority of consumers, luxury, etc..
We enthusiasts might buy a car that has vibration at certain RPM range or idle with heavy cams etc.. but the majority which are the actual profit targets wont buy. The RS is supposed to be a bare bones race car version of the evo. No CD player, No power windows, No sound deadening etc.. but yet Mitsu still added AC on the US cars? Why is that ?
One side of the coin assumes BS’s are needed for longevity of the motor. The other side says there are similar motors that dont have them. If we use the oem Mirage motor parts as delete, is the mirage motor better than the evo to not have it ? Is the Mazda CX-5 2.0L skyactiv-G motor better than the 2.5L skyactiv-G for not having it ?
All inline 4 motors from my understanding produce these secondary vibrations . Perhaps, it is a luxury addition, based on a few things such as Power output, displacement etc.. that determines if BS’s are needed.
I’m not saying I'm right. Just sharing a few things for healthy discussion.
Excellent points but IMO the role of the balance shafts in a stock engine is to be functional rather then for compliance. BS make it run smoother, extend bearing/crank life, rattle the engine less, have less chance of bolts (flywheel) falling out. A side effect is a smoother feel in the seat . Some luxury to our fancy lancers.
If things are vibrating at idle , they are going to vibrate elsewhere. Whats taking place at 8000? Crankshaft flex is a real issue and often overlooked as these cars are modified. Bearing wear,cracking are extreme examples of what harmonics can do.
As far as adding AC to the RS, they knew Americans would require it and it helped sell cars. We are generally big people with bigger appetites.
Why did the US Evo platform come with incorrectly stacked rear diffs? Some theories are they wanted to avoid customer complaints dragging a tire into a parking spot at Mcdonalds. The Ford exploder had a service bulletin years back because the rear lsd diff was noisy or clunked. The Fix, Friction modifier was added to allow more slip. Great for some consumers, bad for others.
There was also a higher chance of crashing when power oversteer is on tap with the Evo platform. Have to protect people from themselves . Its something thats getting worse with time. Its a car manufacture that looks at all the data to decide on what path to take.
Since there's much speculation as to the cause of the secondary vibration that balance shafts were invented to correct, here's the explanation. Its a geometry problem.
When a crank moves 90 degrees from the top dead centre (TDC) in a single cylinder engine positioned upright, the bigend up-down position is exactly at the half-way point in the stroke, but the conrod is at the most tilted position at this time, and this tilt angle makes the small-end position to be lower than the half-way point in its stroke.
Because the small-end position is lower than the half-way point of the stroke at 90 degrees and at 270 degrees after TDC, the piston moves less distance when the crank rotates from 90 degrees to 270 degrees after TDC than during the crank rotation from 90 degrees before TDC to 90 degrees after TDC. In other words, a piston must travel a longer distance in its reciprocal movement on the top half of the crank rotation than on the bottom half.
Assuming the crank rotational speed to be constant, this means the reciprocating movement of a piston is faster on the top half than on the bottom half of the crank rotation. Consequently, the inertia force created by the mass of a piston (in its acceleration and deceleration) is stronger in the top half of crank rotation than on the bottom half.
So, an ordinary inline 4 cylinder engine with 180 degrees up-down-down-up crank throws may look like cancelling the upward inertia created by the #1-#4 piston pair with the downward inertia of the #2-#3 pair and vice versa, but in fact the upward inertia is always stronger, and the vibration caused by this imbalance is traditionally called the Secondary Vibration. - Wikipedia
Just some food for thought...since inline four cylinder engines inherently incur high NVH, what do the Japanese high performance motorcycle engine designs look like in reference to balance shafts? I know they are smaller, thus incur less of a NVH penalty, but I was curious if they even attempted balance shafts in their designs.
I'm no engineer, but the NVH penalties of the four stroke design are cancelled out by the balance shafts, not eliminated. Think of those Bose noise cancelling headphones...you can't hear outside noises, but that doesn't mean they aren't occurring. I can't see eliminating balance shafts causing excessive bearing wear, just vibration. Changing internals without a floating damper, though, I do. The frequencies of the new internals MAY have changed from the stock internals do to weight differences and rpm gains, and will cause excessive twisting of the crankshaft. The stock damper cannot alter its harmonics and as a result cannot account for the change, let alone the increased torque applied due to power gains causing higher loads on the bearings and the oil. These forces have to absorbed somewhere, either the bearings and oil, or through a vibration damper. I'll take the damper for $400, Alex (Trebek).
Good discussion guys!
It just occurred to me that lightened flywheel is actually worse fir crank flex. Not because of engine making power but because there is less inertia to launch car. All the torque to spin wheels comes more from pistons with lightened flywheel. Heavier flywheel would transfer this stored energy from 2-step rpm so the engine doesn't need to work as hard to push crank. Interesting...
Originally Posted by Abacus
Excellent points but IMO the role of the balance shafts in a stock engine is to be functional rather then for compliance. BS make it run smoother, extend bearing/crank life, rattle the engine less, have less chance of bolts (flywheel) falling out. A side effect is a smoother feel in the seat . Some luxury to our fancy lancers.
If things are vibrating at idle , they are going to vibrate elsewhere. Whats taking place at 8000? Crankshaft flex is a real issue and often overlooked as these cars are modified. Bearing wear,cracking are extreme examples of what harmonics can do.
As far as adding AC to the RS, they knew Americans would require it and it helped sell cars. We are generally big people with bigger appetites.
Why did the US Evo platform come with incorrectly stacked rear diffs? Some theories are they wanted to avoid customer complaints dragging a tire into a parking spot at Mcdonalds. The Ford exploder had a service bulletin years back because the rear lsd diff was noisy or clunked. The Fix, Friction modifier was added to allow more slip. Great for some consumers, bad for others.
There was also a higher chance of crashing when power oversteer is on tap with the Evo platform. Have to protect people from themselves . Its something thats getting worse with time. Its a car manufacture that looks at all the data to decide on what path to take.
I agree with what you're saying. We are here to understand what parts appear to do and by better understanding, we can make an informed decision.
My thinking is the engine is balanced when stock. We make it a little more off-balance with each mod. There will be a point where the off-balance is so much that removing the BS wouldn't make engine worse. I also think this point is when we change the bottom end.
Rotational off balance isn't as bad as lateral vibrations. The clutch is designed to transfer rotational energy from engine to transmission, so the pulses of power won't be a problem. Now, if we get vibrations where clutch is moving sideways (forward and backwards if sitting in car) from the clutch's view, your clutch is forced to clamp disk at angle that isn't rotational. This is what Jack's Transmission was showing in pictures of worn clutch disks where the outside material started chipping off since nothing is resisting that sideways force, so the weakest areas start falling off.
Again, this is likely from shifting at high RPM ranges. I use my 2-step launch control and then shift at 8000rpm, so I have no plans on removing my BS.
Both my previous Evo IX and current Evo VIII i have the balance shaft installed. On my IX went through a few clutches and one of them was a sprung 6 puck ceramic. I went to the track and miss shifted from 2nd at 7k rpms back to 1st. I dont know how many RPM’s it jumped to but as quickly as I could I pushed in the clutch and threw it in neutral. Motor was still good, compression perfect and I could drive the car still. It just didnt feel as smooth as before when engaging the clutch. Long story short I soon after changed my clutch and the edges were chipped and material chucks broken off similar to those pictures. Now I am not sure are those Jack’s personal car or something the owner didnt tell Jack’s ? For all we know Jack’s could have just seen that the BS was gone and this is how the clutch looks but knowing how it was driven.
Originally Posted by Abacus
Excellent points but IMO the role of the balance shafts in a stock engine is to be functional rather then for compliance. BS make it run smoother, extend bearing/crank life, rattle the engine less, have less chance of bolts (flywheel) falling out. A side effect is a smoother feel in the seat . Some luxury to our fancy lancers.
If things are vibrating at idle , they are going to vibrate elsewhere. Whats taking place at 8000? Crankshaft flex is a real issue and often overlooked as these cars are modified. Bearing wear,cracking are extreme examples of what harmonics can do.
As far as adding AC to the RS, they knew Americans would require it and it helped sell cars. We are generally big people with bigger appetites.
Why did the US Evo platform come with incorrectly stacked rear diffs? Some theories are they wanted to avoid customer complaints dragging a tire into a parking spot at Mcdonalds. The Ford exploder had a service bulletin years back because the rear lsd diff was noisy or clunked. The Fix, Friction modifier was added to allow more slip. Great for some consumers, bad for others.
There was also a higher chance of crashing when power oversteer is on tap with the Evo platform. Have to protect people from themselves . Its something thats getting worse with time. Its a car manufacture that looks at all the data to decide on what path to take.
Yes I agree the BS is for function and not compliance. I was just pointing out many things engineers are forced to do and not just because its needed for longevity . The function of BS's may be luxury purpose because auto makers have to sell to Mass consumers for profit. The majority of consumers would not like extra vibration at certain rpms and they may think the engine doesnt “feel reliable” and that would not be good for sales.
Then there is also motors inline 4 that dont have balance shafts. So why do they not require them if it is so important for longevity ?
There might be vibrations that will hurt the motor and there are vibrations that annoy the driver. How do we know which vibration the BS is softening/canceling ? Any way to check frequencies and any data that says x range of frequency = bad for bearings etc..?
I previously mentioned I removed the BS on my old Sentra back in the day. Idle was smooth and most rpms were smooth. The only ever so slight vibration I felt was on the steering wheel not really on the seat and it was around a certain rpm range , if I remember correctly around 3.5k-4.5k .
I’m interested to see where this leads, how we calculate or test things and what we find out. We all are making good points and it might lead to something..
Last edited by BluEVOIX; Feb 17, 2018 at 01:07 PM.
Bearings shouldn't wear more, now that I think about it. It seems more and more to be to help everything else outside of engine to have longer life. The only concern inside the engine for me is the oiling squirters. It may miss target slightly, but using better oils will help with that (another day's research).
As long as engine is allowed to vibrate, bearings should be happy. But if someone removes all the rubber from engine mounts, then I can see more wear since the bearings will deal with the off-balance.
Originally Posted by drive955i
Just some food for thought...since inline four cylinder engines inherently incur high NVH, what do the Japanese high performance motorcycle engine designs look like in reference to balance shafts? I know they are smaller, thus incur less of a NVH penalty, but I was curious if they even attempted balance shafts in their designs.
I'm no engineer, but the NVH penalties of the four stroke design are cancelled out by the balance shafts, not eliminated. Think of those Bose noise cancelling headphones...you can't hear outside noises, but that doesn't mean they aren't occurring. I can't see eliminating balance shafts causing excessive bearing wear, just vibration. Changing internals without a floating damper, though, I do. The frequencies of the new internals MAY have changed from the stock internals do to weight differences and rpm gains, and will cause excessive twisting of the crankshaft. The stock damper cannot alter its harmonics and as a result cannot account for the change, let alone the increased torque applied due to power gains causing higher loads on the bearings and the oil. These forces have to absorbed somewhere, either the bearings and oil, or through a vibration damper. I'll take the damper for $400, Alex (Trebek).
At 7000 rpm, your speed is 60mph. Going back to 1st gear, it's just under 10,500 rpm if your clutch was fully engaged.
When your Sentra had vibrations at 3500 rpm, was it worse at 7,000?
Originally Posted by BluEVOIX
I went to the track and miss shifted from 2nd at 7k rpms back to 1st. I dont know how many RPM’s it jumped to but as quickly as I could I pushed in the clutch and threw it in neutral. Motor was still good, compression perfect and I could drive the car still. It just didnt feel as smooth as before when engaging the clutch. Long story short I soon after changed my clutch and the edges were chipped and material chucks broken off similar to those pictures. Now I am not sure are those Jack’s personal car or something the owner didnt tell Jack’s ? For all we know Jack’s could have just seen that the BS was gone and this is how the clutch looks but knowing how it was driven.
I previously mentioned I removed the BS on my old Sentra back in the day. Idle was smooth and most rpms were smooth. The only ever so slight vibration I felt was on the steering wheel not really on the seat and it was around a certain rpm range , if I remember correctly around 3.5k-4.5k .
FWIW, The mention of ( main ) bearing wear is an extreme example of harmonics, vibration and crank flex in a built high hp stroker/engine. Its not clear to any of us what exactly is taking place within the 4g63 engine and what the engineers thought when they designed it.
I was speculating as we all are on what exactly goes on with the BS in the 4g63 engine.
Regardless, I think we all can agree that on a built engine they need to be deleted and that a good harmonic dampner should be used.
I just read through the wikicars link you sent me. Mitsubishi did their homework by designing the 4G63 with short stroke. This helps with the harmonics. It's interesting they called the power stroke imbalance as second order vibration. I need to reread it a few more times to fully understand.
Can someone confirm that the rear BS rotates in the same direction as the crankshaft?
Originally Posted by drive955i
Just some food for thought...since inline four cylinder engines inherently incur high NVH, what do the Japanese high performance motorcycle engine designs look like in reference to balance shafts? I know they are smaller, thus incur less of a NVH penalty, but I was curious if they even attempted balance shafts in their designs.
I'm no engineer, but the NVH penalties of the four stroke design are cancelled out by the balance shafts, not eliminated. Think of those Bose noise cancelling headphones...you can't hear outside noises, but that doesn't mean they aren't occurring. I can't see eliminating balance shafts causing excessive bearing wear, just vibration. Changing internals without a floating damper, though, I do. The frequencies of the new internals MAY have changed from the stock internals do to weight differences and rpm gains, and will cause excessive twisting of the crankshaft. The stock damper cannot alter its harmonics and as a result cannot account for the change, let alone the increased torque applied due to power gains causing higher loads on the bearings and the oil. These forces have to absorbed somewhere, either the bearings and oil, or through a vibration damper. I'll take the damper for $400, Alex (Trebek).
Last edited by 2006EvoIXer; Feb 17, 2018 at 02:51 PM.
How exactly does dampener work? The front BS is the only thing spinning in reverse direction of the crank, so I think that it is naturally better to keep and modify with engine builds. I think it should help balance engine at all RPMs.
These things? These things will cause engine, tranny, and transfer case to twist more. I'm not sold that this is good to use.
Originally Posted by Abacus
FWIW, The mention of ( main ) bearing wear is an extreme example of harmonics, vibration and crank flex in a built high hp stroker/engine. Its not clear to any of us what exactly is taking place within the 4g63 engine and what the engineers thought when they designed it.
I was speculating as we all are on what exactly goes on with the BS in the 4g63 engine.
Regardless, I think we all can agree that on a built engine they need to be deleted and that a good harmonic dampner should be used.
Last edited by 2006EvoIXer; Feb 17, 2018 at 02:17 PM.
How exactly does dampener work? The front BS is the only thing spinning in reverse direction of the crank, so I think that it is naturally better to keep and modify with engine builds. I think it should help balance engine at all RPMs.
These things? These things will cause engine, tranny, and transfer case to twist more. I'm not sold that this is good to use.
Both BS would need to be deleted.
An Harmonic balancer
Thanks for the links! I just realized that all our accessories (alternator, A/C, power steering) helps too!
These harmonic balancers should be installed with power upgrades to smooth out the power pulses from power strokes between the cylinders. This should cushion power pulses by absorbing the engine acceleration between TDC and 90 degrees and deceleration of compression stroke (90-180 degrees) of opposing cyclinder (this is where momentum is released to help with compressing), but it won't help with crank twisting since it's on opposite side of clutch so energy still travels through the crankshaft, twisting it more at launches.
Originally Posted by Abacus
Both BS would need to be deleted.
An Harmonic balancer
This crankshaft pulley harmonic balancer will make the turbo feel laggier, but it will help with launch control where RPM will be slightly higher after tires hook up.
Seems a shock absorber like that would be used to quell exterior engine vibrations that balance shafts and vibration dampers attempt to quell on the engine’s interior. Don’t get me wrong, I understand the reason for installing it, but I wouldn’t call it an adequate replacement for a quality damper or balance shafts.
Feb 17, 2018, 12:06 PM
