Let me know your thoughts! Many of you may think tl;dr, but this is worth your time.
http://www.jackstransmissions.com/pages/keep-your-balance-shafts
http://www.jackstransmissions.com/pages/keep-your-balance-shafts
A different side, taken from DSMtuners:JacksTransmissions said:Keep Your Balance Shafts
Removing your balance shafts is a bad idea. It should never be done and anyone who has removed balance shafts will suffer issues which can be irritating and confusing.
We used to be a company, just like all others, which encouraged customers to remove their balance shafts. We used to say that they were there for driver comfort and that removing them would increase oil pressure and help with reliability. We were wrong. It's hard to admit that you are wrong with something which has been widely accepted in the DSM and EVO community, but removing balance shafts is one of the worst things you can do to your car. So we are going to be the first to admit that through the past 13+ years, we were wrong.
Why is it such a bad thing? Well, experience counts, and what we are going to share with you are the things we have learned to come up with the conclusion that you need to keep your balance shafts. We hope this small article will educate people to keep their shafts and not remove them.
What balance shafts do is something terribly important. They drastically reduce engine crankshaft harmonics and torsional whip. What is torsional whip? Torsional whip is created in all piston engines. The whip is essentially the crank twisting back and forth due to the nature of how a piston engine works. Think about it. You have a piston which is creating resistance to the crank on the compression stroke. Once the piston hits TDC and your fuel/air ignites, it then quickly changes to adding force to the crank. So on each revolution the crank is being forced to slow down on the first half of rotation, and then forced to speed back up on the second half of rotation. This causes the crank to twist back and forth for every revolution. No matter what the RPM, power, fuel, temp, compression it will always have these forces. As the crank is rotating, it is also twisting back and forth every revolution all of the time.
Imagine the forces the crank has to endure at high RPM. Lets say you are zinging your engine up to 8000RPM. At that speed your crank is twisting forward and back 133 times a second!! This whip is not gentle either, it's like a large hammer beating on your drive-train 133 times a second. When we think of what a crank is going through at high RPM, we think if just how fast it is rotating and how amazing it is that it can hold the power which we are forcing through it, but that's not all. It is also flexing and twisting while it is rotating and 133 times a second at your 8000RPM rev limit. It's something our minds just can't comprehend. This whip creates a series of problems for us.
Torsional whip is very destructive. Bolts will work their way loose in various places, you get a buzz from the engine, clutches drag and break, crankshafts break, the trans rattles and wears out, and the drive-shaft will resonate. What helps absorb torsional whip? Many things, and they are all parts which we comically try to remove when we modify our cars.
The parts which reduce torsional whip are:
The things which increase torsional whip:
- Balance shafts
- Heavy flywheels
- Springs in clutch disks
- Crank damper
- More rotational mass everywhere
How are parts affected by torsional whip? Lets start with the clutch. Ever use a puck disk and notice after a short time that large chunks of the pucks have broken off? We used to think it was a heat issue, but what is in fact happening is the vibrations from the engine harmonics in some cars is so severe that the pads will crack and break off. The disk is buzzing and flexing all over the place at high RPM and this is too much for the pucks. They crack and fling off in time. Some pictures below of this issue:
- Removed balance shafts
- Lighter flywheels
- Unsprung clutches
- Adding stroke
- Raised compression
Many people think that the springs on a disk are there for smooth engagement. This is not correct. The springs are there to absorb crankshaft torsional whip. If you use a solid unsprung disk, you are adding to the whip issue, but using sprung disks in a race car has proven to cause problems as the springs are known to break. This makes things difficult when choosing the right disk for your application.
Excessive harmonics will also kill your expensive lightweight flywheel. Without balance shafts and heavy flywheel weight to absorb the whip, the whip is so violent at your clutch that the end of the crank and flywheel will start fretting and your flywheel bolts will work their way loose. Picture below of a fretting flywheel. When something like this happens the crank also looks this bad and has to be replaced too. This is starting to become very common and here are 2 different flywheels we have at the shop right now below:
Did you break your crankshaft? Why can some people get away with years of abuse and over 1000hp on a crank and you break it in your 16G car? Harmonics. Here is a pic below of a crank which broke due to excessive harmonic and torsional forces. This car had a 16G on it and would have been lucky to make 300hp:
Crank harmonics will also cause clutch drag. If you perform the clutch drag test you will find that we want you to rev the engine high in order to see if the car moves forward. The higher the RPM, the more harmonics are created. What happens is the clutch disk begins to buzz in between the flywheel and pressure plate. If the disk buzzes and flexes too violently, it will make contact and drag. We want our customers to adjust their clutch so that enough room is given in the clutch to allow the disk to vibrate and not come into contact with the flywheel or pressure plate so the trans will shift nicely.
Those which have issues with clutch drag and can't get rid of it are usually people with high compression, added stroke, and removed balance shaft engines. This will create such excessive harmonics that the disk buzzes too violently and the clutch drag can't be eliminated at high RPM. They are then forced to switch to a 7.25" twin disk, which in our option is a horrid clutch for the street or drag racing. The reason a 7.25" twin does not drag is due to the size. It is smaller in diameter so the end of the disk will travel a shorter distance which will reduce its chances of dragging. The size is what prevents the disk from moving far enough to hit anything.
Excessive whip will also kill your trans synchros in time. If you have a Jacks Transmission we have found a solution so the synchros will live, but if you do not, you may experience synchro failure due to synchro mushrooming. Tech article about synchro mushrooming and spring failures HERE.
Torsional whip will resonate through your trans and cause accelerated spline wear. Remember the whip can be very violent and is at a high frequency, so everything in your drive-train is taking a beating. Are your t-case output shaft splines saw-toothed? Pictures below of spline wear from cars with excessive whip:
Excessive torsional whip is hard on gears too. Not only do the gears need to deal with your added torque and harshness of your clutch, but they take a beating from the torsional whip too. It's like the added torque isn't enough, we have to beat on them with a hammer over 100 times a second too. Without anything to absorb the abusive whip it goes right into the gears inside your trans. In time they will fatigue and break. No need for big power to break gears thanks to the whip. If you keep killing gears at a power level that shouldn't, then you could have a harmonics issue:
We have many people which complain about a noise they hear during cruise or coasting in gear. We call it the 'womp womp' noise. It's a rattle you hear which resonates through the clutch, trans and drive-shaft, but most of it comes from the drive-shaft. Can you guess at this point what is causing that noise? Torsional whip. You can replace your trans, drive-shaft, t-case, rear end and it won't make a difference. The noise will always be there unless you find a way to reduce the whip from the engine.
We see it all of the time. We have a customer come in with a car for the 60k timing belt service. The car is smooth, quiet and shifts perfectly at high RPM when they drop it off. During the timing belt job they want us to remove the balance shafts (which is an 'upgrade' many like to have performed). Once the balance shafts are removed parts vibrate, clutch drags, and engine feels so buzzy that the interior of the car now makes noise. In our opinion, the car is ruined. It was so nice when it was smooth and quiet and now it's a buzzy mess.
So what we have learned is this- we know you want to modify your car so there may be no way around using an unsprung clutch, lighter flywheel, higher compression or added stroke. You have to use those parts to go fast, but one thing you can keep which will absorb a lot of those added harmonic creating mods is your balance shafts. The 4G63 balance shafts do an amazing job of absorbing all of these excessive harmonics and torsional whip. Just keep them in there.
We know, we know. The balance shaft belt can break and you are all worried about that. Simply use a Kevlar belt and maintain the system properly.
Yes, we know... You had your engine balanced and blue-printed when it was rebuilt. It doesn't matter. Torsional whip has nothing to do with how well your engine is balanced.
Yes, we know you will be worried about oil pressure losses due to the balance shafts. This is a myth. The oil pumps found in the 4G63 are very high volume and you will see absolutely NO difference in oil pressure with or without your balance shafts. We have had cars come into the shop knocking with no rod bearings left in the engine and the oil pump works so well that the oil pressure still showed normal readings. You can have a bearing completely missing from the 4G63 engine and the oil pressure will look perfect. Oil pressure losses due to balance shafts is BS.
You want to zing your engine to the moon for some reason and believe the balance shafts will break somehow. In the 13+ years we have been building 4G63 engines, we have never seen a balance shaft that had failed/broken. This is not to be mistaken with an engine that is ill kept and is old and worn out. If your engine is worn out, you risk spinning a balance shaft bearing. Your rod bearings are about the spin anyway so what's the difference? If you keep your oil level up and maintain the engine properly your balance shafts will be fine. If you are super worried about them, get the EVO balance shafts as they are slightly more arrow dynamic. Now you can sit at 10K all day and impress your friends.
Next you are probably asking if the balance shafts will rob too much power and your 16G will not hit your 9 second goals. Yes, it will take an un-noticed amount of power away, but it will be made up by the ability to shift your car at high RPM and will give you some torque which the 4G63 is always lacking anyway, so it's actually a nice thing to have that added torque. Just remember that more rotating mass means more torque and what better way to give your engine that much needed torque for the street than to reinstall your balance shafts.
Why do you think the manufacturer installed the balance shafts in the first place? Why did they use such heavy flywheels and sprung clutches? To reduce the harmonics. Many luxury cars have dual mass flywheels to try to take even more away. Many BMWs come with dual mass flywheels now. What do most BMW owners do the first time they touch their clutch? They remove their dual mass flywheel and install a standard light weight flywheel... Then they start to have 3rd gear synchro issues, they tear and break the rubber insulator flex joint and the car becomes unreliable. It's like us with the DSMs and EVOs. We just insist that we remove and throw away all of these carefully engineered and much needed parts for reliability.
We get it. It's hard to believe that something we all thought was the right thing to do is now wrong. Those of us which have spent a lot of time and money rebuilding our engine without them may fight to prove removing them was right. It wasn't the right choice and we would recommend finding a way to pop them back in.
If you reinstall your balance shafts your trans will shift much better at high RPM and much of the drive-train noises you hear will be reduced. We will say again that your trans will shift a lot better with balance shafts in it! This change in shift quality is actually quite shocking! You want a trans that shifts nice? Stick those balance shafts back in that engine!
We used to think the balance shafts did nothing to absorb whip and harmonics. We thought there had to be something in-line with the crank in order to reduce this stress, but as it turns out that's not the case. The balance shafts are attached to the crank via belts, but it works. We have proven to ourselves here over and over again that they work and better than anything else you add or remove from your car. Just keep them in there. Keep your car smooth, reliable and more pleasurable to drive.
If you have any questions regarding balance shafts and if you should remove them or put them back in, please email us at sales@jackstransmissions.com
LandSpeed-DSM said:The flywheel, clutch, changes to stroke or compression are all things that effect whip and harmonics in the crank.. but not the balance shafts.
The balance shafts are only connected to the crank by what is basically a rubber band.
The problem is the difference in acceleration from piston to piston as they rise and fall in the even fire configuration. One will be on compression, the next on power, another on exhaust and the last one intake. All of these events contributes to the overall net torque and cause the crank to bend and vibrate.
The balance shafts do not directly affect this. They simply add a new vibration 180* of the second order harmonic being put off by the crank.. this is to "hide" the crank harmonics for cabin NVH considerations.
The balance shafts themselves have no effect on your shifting or providing any aid to the crank like increasing the weight of a node (flywheel for example)
If you are really keen to learn more, start with a paper like this:
Torsional Vibration in Automobile Engine Crankshafts
And here:
http://www.bhjdynamics.com/downloads...amper_Info.pdf
Or here:
http://www.epi-eng.com/piston_engine..._absorbers.htm
Quote:
Originally Posted by gusu
No it's not new. It's something you have a hell of a time fighting when trying to get a engine to rev past a certain point.
The engine design and balancing skills required to reduce it to levels where high RPMs are possible is a bitch. That is why the full race version of the 4AGE by TRD is capable of 240hp at 11k RPMs (Technically they make that at 8600 RPMs but the car continues to rev past that point). The motor is built from the ground up to reduce these vibrations.
If you want a more in depth article on the subject a few Formula 1 engine builders have covered the topic in insane detail. I couldn't imagine the skill required to make a engine capable of 18-24k RPMs. I know F1 now limits engine speed to 18k RPMs but that wasn't always the case.
Which reminds me, if you've never seen the old footage of Senna racing in the rain it's a must watch. The guy was unbelievable in the rain and would lap the entire pack just simply because he was a god at driving in the rain.![Image]()
Which is precisely why in my ~10.5k rpm motor.. I don't want a pair of balance shafts spinning at nearly 21000rpm, weighing in at a couple pounds each.
That is a bomb waiting to go off.
