2006EvoIXer

iTrader: (1)

Attempt #1 was a failure. Sorry about that! I'm still learning/relearning myself since I don't think about this every month.
I do want to provide good info to help people fully understand their decisions.

Here is attempt #2 to provide some solid basic knowledge. I am not a mechanical engineer, BUT I will use info provided by one. Just to start off with some basic info, let's start with primary harmonics, which means frequency is the same as RPM. Enjoy this video, he's a mechanical engineer and does a good job explaining:


Next up, secondary harmonics, which means vibrations at double the frequency of RPM.


The way I view this is the stress the crankshaft sees. Orientation is looking at engine from front right wheel. From TDC (0°) to 90° crank rotation, it is accelerating piston to max velocity (speed). From 90° to 180° (BDC) crank rotation, crank is stopping the piston from max velocity to zero. Then it repeats again on second half of crank rotation (BDC to 270° and then 270° to TDC). Every time forces change directions, it causes a vibration. Since the forces change every 90°, it changes 4 times per RPM, which is 2 full cycles (one cycle is when forces changes directions twice: up and then down to original position).

So now we know what secondary harmonics are, here is how Balance Shafts (BS) work to counter the harmonics:


If you pay attention to the harmonic curves, you will noticed that the BS harmonics are in opposite harmonics from the engine. So when people claim that going to a 2.3L changes the hatmonics completely and the BS won't do anything, that is incorrect. By increasing stroke, the secondary harmonics curve have higher extremes (top and bottom curves). But the BS will remain the same. So theoretically, it does help with secondary harmonics in a 2.3L. It reduces the curve tops and bottoms to make less vibrations. And since BS are getting its rotation from the timing belt or BS belt, which are both tied to crankshaft, the timing of BS secondary harmonics WILL always be in tuned with crank (unless the BS wasn't timed correctly, of course).

Also notice, secondary harmonics is not tied to piston position because that is the primary harmonics, which BS is not designed to cancel out. The center pistons cancel out the outter pistons' primary harmonics.

2006EvoIXer

iTrader: (1)

Attempt #2 in progress...

This part is reserved for design of balance shafts. This part will take some good visualization in your head!

Let's take a moment to think about the 4 strokes of the engine. Intake (going down), compression (going up), power (going down), and exhaust (going up). Which stroke causes the most vibrations? My opinion is the power stroke at ignition is the most violent (combustion of fuel). This explosion pushes the pistons down at extreme forces that it accelerates the pistons to amazing speed by crankshaft 90° (we will discuss the actual speed later) and in a distance of about 58.58% of your crankshaft stroke (so 58.6mm down for a 2.3L).

Anyway, let's look closer at the BS movement as power stroke of each cylinder. Looking from passenger wheel at engine, as explosion pushes pistons down on crankshaft in clockwise rotation, the BS weights are rotating upward with weights on outside. No counter balance there since both forces are in same direction (downward). Piston accelerates to max speed by crankshaft 90°, the BS weight is at TDC. This timing is interesting because at this position, the crankshaft has to stop the piston from max speed to zero by BDC. Also, realize that piston has already traveled 58.6% of the full crankshaft stroke, leaving only 41.4% of the stroke to stop the piston. Interesting! Is this where BS does it's work?

Explosion pushes pistons to accelerate to extreme speeds, but because of geometry of how pistons transfer vertical energy to rotational crankshaft energy, the crankshaft has to stop piston speed with remainer 41.4% of the distance. So how does BS being at TDC work when pistons are starting to decelerate from max speed to zero?

Let's look at the physical connections of BS to crankshaft. The BS spins with extra weight on one side (lop sided). As it spins, force is pushed in direction of where the weight is onto journal bearing. There is a thin high pressure oil film getting compressed to transfer the force to bearings (front and rear) that pushes on the block. The block will vibrate ever so small of a distance. As block is vibrating up when BS is at TDC, the crankshaft will be exerting a force to slow piston down, which is an upward force. I think this tiny vibration tightens up the oil gap in the main journal bearing to help stop the pistons more efficiently. Now, going back to TDC at ignition where BS is pushing down, this creates are downward vibration to increase the oil gap in the crankshaft to bearing and should give an ever so slight increase to give power stroke more oil cushion and allows bearings to live longer by reducing the chances of contact at the highest force (TDC). Considering main bearing clearances are usually 0.003", I think BS actually helps extend bearing life. At the same time, it helps reduce vibrations by tightening up the clearance at the highest stress situation and increase clearance at most critical situation when power is getting transferred. I believe it becomes more beneficial as revs increase.

There are much discussion that if displacement is changed, that these BS don't do anything. I disagree because the timing with BS and power stroke is still the same. Yes, it won't be as effective for higher hp builds, but it does help. Again, my opinion.
Can engine builders verify if main bearing wear is at bottom half? I'll continue write-up as I find time.

2006EvoIXer

iTrader: (1)

This part is reserved for discussion on difference as balance shafts are removed.
Without BS installed, this benefit of creating a slightly larger clearance at TDC when fuel is ignited and tighten during start of deceleration of pistons, I can see main bearings wear out faster of high hp builds. This does increase vibrations since there is slightly more slack during deceleration and less slack during acceleration from combustion. How much will depends on power output. Again, this is all theory.

2006EvoIXer

iTrader: (1)

This part is reserved for those that decide to delete balance shafts. What options are available and what I'd use if I'm deleting mine.

My thought on the 2 versions of BS delete available (GSC race and stubby). The oil pump will have resistance as gears accelerate. The stubby shaft is fine for most engine builds, but if the engine will be pushed to limits with high instant power transfer (torque) like severe antilag, that instant power surge puts oil pump gears into stress. The stress will push gear contact areas apart with violence.

In short, although the oil sprocket is resisting timing belt forces of being pulled inward, the oil pump gear on the other end is being pulled diagonally forward and downward. Under extreme acceleration (spinning up), the upper oil pump gear will have resisting force pushing down. At the same time, upper oil gear has to resist an upward force. This is the force the stubby shaft resists. I would worry that using severe antilag will shock the gears with instant torque and will wear out the oil pump journals (not just at the stubby shaft, but also at the sprocket) quicker.

For me, personally, when I pull apart my oil pump, I would make sure the 2 oil pump gears fit snug and tightly together. In addition, I would use the full length GSC race shaft to make sure the top oil gear holds its position with less risk of building backlash/slack over time. This slack will start hammering the oil gear journal bearings over time. But that's just me being careful.

MinusPrevious

iTrader: (3)

One question is this: Is "Jacks Transmissions" White Paper on Balance Shafts correct or not?
https://www.jackstransmissions.com/b...balance-shafts

Lumpy Sticks

iTrader: (3)

Joe - I would 100% disagree with what Jack's says. If that was the case a lot of other production cars with I4 engines, iron blocks and DOHC would be having issues. But they dont. I am willing to bet more I4 engines dont have balance shafts then ones that do.

Obviously I am a fan of no balance shaft. That's why I took the ones out of my bugs engine. It spins to 8500 rpm and there is a big plus to removing them. There is another article from another company I need to find and post. Let me look for it.

2006EvoIXer

iTrader: (1)

My goal is to allow everyone to decide for themself after getting a good understanding of how balance shaft works (at least my understanding). I can be wrong and have no problems updating as needed, so I'm hoping for lots of input.

kikiturbo

not correct... any type of transmission issue related to crank harminics has to do with torsional damper that is on the end of the crank and/or use of rigid clutch plates

Biggiesacks

the forces acting on the engine that create those vibrations are there regardless of the shafts or not. The shafts just cancel out the vibrations so you don't feel them, that doesn't mean they aren't happening. At least that's how I understand it.

kaj

iTrader: (60)

If someone could explain to me why a 4g63 needs balance shafts while spinning to 7200rpm, then I'll buy in.
I'd be more inclined to believe they are there because the casual consumer wants their sports car to drive as smooth as a Toyota

IMO anything more than that is just over thinking.

kikiturbo

there is a great writeup on wikipedia about secondary order vibrations: https://en.wikipedia.org/wiki/Engine_balance#Rocking

In short... pistons travel more in top half of crank rotation than in bottom half due to rod angle. That is why even while we have pistons travleling in opposing directions the engine is not perfectly ballanced and you get second order vibrations.

Edited in.. the ammount of vibration force is proportional to crank stroke and inversly proportional to rod length.. that is why you need ballance shafts more in 100 mm crank engines than on 88 mm... and why long rods are great..

One piece of trivia I didnt know... even though ballance shafts are used by many, the original idea came from Mitsubishi..

kikiturbo

exactly..

ConEvo

Personally, i chose GSC Race Balance Shaft which is the middle solution between these two. What I mean? Instead for either keeping the heavy balance shaft, or deleting them completely, this solution gives you the ability to keep the one balance shaft (oil) and the other deleting it, without completely removing it. This way, you have a much more lighter rotating mass, but without the risk of detroying the oil pump. The OEM balance shaft is 943gr each, therefore 1,886gr, in contrast with GSC which is only 192grams only. I have the pictures at my phone if you like to upload them later on. With these in mind, this was the reason for keeping balance shaft but with a much more reduced rotational weight.

Regarding vibration. I have two inputs, both with GSC's. My car has some vibration at idle but mainly because of the lightweight flywheel, in contrast with my brother's evo which has minimal to not existent vibration on oem flywheel. Keep in mind that both cars have oem mounts which also play a major role in transferring vibration to the interior and especially at idle

2006EvoIXer

iTrader: (1)

Thanks for the comments, some are jumping ahead while others give me more reading to do..
Once I get through my brain dump of thoughts, I'll read links and search for more info to incorporate..

Biggiesacks

I've never seen a stub helical gear related failure of an oil pump before. Doesn't mean it hasn't happened though.