kyoo

iTrader: (29)

i dont think this one ever gets mentioned often enough, but do it or not - get a fluidampr crank pulley (https://stmtuned.com/products/610701...3-crank-pulley)

i think that may be more important than balance shafts or not. note, it will not help with the vibration of removing balance shafts

LetsGetThisDone

iTrader: (1)

I've watched that video many times over the years as people reference it to keep balance shafts to prevent clutch drag/shift lock out. That is simply not the reality.

Balance shafts are tuned to work in a fairly specific RPM range, in the Evo it's around the cruise RPM's, 3-4000. Out side of that, if you have a properly balanced rotating assembly and good harmonic damper, you don't even know the shafts are gone. My car with the ATI you can't even tell, even cruising at 3500rpm with poly motor mounts.

Evo9isLife

Im assuming you are assembling an aftermarket rotating assembly, if so you should definitely remove the shafts. My understanding is that the oem shafts are specifically designed to reduce the harmonics/vibration of the oem rotating assembly in a specific rpm range. Once you change the internals which have very different weights and materials creating their own unique harmonics, the balance shafts become useless since the harmonics have changed. At that point they are just another potential failure point that will take out your new engine.

Ayoustin

iTrader: (2)

Balance shafts are only for NVH as stated. They will do nothing to prevent clutch failure or rotating assembly damage. I don't know how Jacks came to that conclusion but it is outright wrong. They will still work with aftermarket rotating assemblies, there is still spinning weight doing the same thing at the same time, just a different amount of weight so they may not decrease vibes like they do on a stock rotating assembly. Whether they stay in or come out should be determined by your tolerance for NVH and whether or not the extra simplicity and couple extra HP is worth it or not.

Harmonic/crankshaft balancers/dampers do not serve the same function as balance shafts, they exist to reduce torsional vibrations in the crankshaft, this has an appreciable difference on how long a crankshaft lives under high load. OE crank dampers are made with a bonded rubber middle element and that rubber hardens from time and heat exposure, investing in something like a Fluidampr or ATI damper is pretty worthwhile and easy to change out.

I've worked for OEMs doing both balance shaft and crank damper development, they both play the same role (I'm not saying they both do the same job) regardless of the engine in question. Balance shaft failures are rare, but at the end of the day they are an extra toll on power, the oiling system, add weight and complexity to the engine although they are not unwelcome in a street car. Crank dampers are paramount in keeping a rotating assembly together. Left unchecked, torsional vibrations destroy crankshafts and bearings in pretty short order.

mitsuatb

iTrader: (6)

All 4 cyl inline engines have a secondary imbalance due to velocity variation along the length of the stroke because the rod effective length changes.

This can not be damped or balanced out with a static system. The balance shaft can cancel this vibration it is the only way and why it is fitted to the 4G63.

If you keep the total weight of the rod piston the same and just change replace parts the balance shaft will still work like OEM.

Lighter or heavier may cancel part of the balance shaft effect it will still cancel some of the imbalance but may over/under compensate for a very light/heavy reciprocating mass total.

LetsGetThisDone

iTrader: (1)

Yes. The bshaft is to cancel 2nd order vibrations. It is purely for NVH/occupant comfort.

RallySport9

iTrader: (20)

Wrong. You're just plain wrong. Balance shafts/crank dampers have an extremily important roll in reducing engine vibrations/leveling engine harmonics to reduce the wear on bearings. Sad when someone can't admit they were wrong and spread misinformation to affirm their position for the sake of their ego.

kyoo

iTrader: (29)

the harmonic balancer/crank damper is not the balance shaft... i dont have balance shafts anymore. I do have the fluidampr crank damper

https://www.maperformance.com/produc...uidampr-610701

the video you linked even makes the distinction between balance shafts and harmonic dampers at 6:50... i dont get it, is your post a joke?

"you could take off the balance shaft and put one of these (fluidampr harmonic balancer) in and your engine is protected. people just have a hard time wrapping their heads around that" ~7:20

RallySport9

iTrader: (20)

Yes thats true as he said. If you get the fluidamper it can take over the jobs of the balance shafts but no the same way. If you continue watching he explained the different types of vibration. crank dampers are for combustion vibrations while balance shafts are for balance vibration any form of vibrations put extra strain on engine internals. The factory made them for that reason.

kyoo

iTrader: (29)

i mean i dont really care one way or another but there are benefits, i.e., the balance shaft belt spins at like twice the speed of the motor or something like that. i'm a big proponent of having balance shafts on street cars but my car is primarily time attack now. i'd get the fluidampr even if i had balance shafts still. it's a different internal vibration, though it did smooth out my revs quite a bit. that, and the tune i recently got

RallySport9

iTrader: (20)

Duhh..of course they're not the same thing, never said they were but they both are meant to reduce vibrations of different engine movements. As they talk about right after that sentence you quoted. Balance shafts can't replace the job of harmonic balancers and harmonic balancers can't replace the job of balance shafts. You can just never convince some people... whatever, enjoy premature engine wear.

kyoo

iTrader: (29)

my evo is almost exclusively used for time attack lol

Abacus

iTrader: (9)

Just my opinion.
Japanese engineers designed the stock 4g63 with balance shafts and the stock bottom end. If you aren’t turning the engine over 8k consistently you can leave them . Let them do the job they were designed to do by very smart people.
Once you build the bottom end the balance shafts need to go . The material and weight difference isn’t going to allow them to work as originally intended.

Most people including myself prefer the stub shaft .
I like the idea of an aftermarket ATI dampener and have one on one of my cars.


However, my 26k well abused 800-1100hp engine has a stock balancer and it was the first import engine a well known domestic builder put together in 2007. Not sure if an ATI was available at that time. It’s a low compression engine with big cams and gets shifted at 9000-9400 . We believe the low compression , professional tuning and frequent oil changes have increased its lifespan.
On paper it doesn’t seem possible the bearings would last with that vibration,harmonics ,rpm and use.
While we are on the subject of cranks.
To add insult to injury it’s using a custom Gsc crank that favors oiling over strength. Stock crank and all recent cranks favor strength over oiling.
Not trying turn this into a bash Manley thread but after guys were rattling them to pieces they also went back to oem style in the last few years. If the crank in those engines was going to break because of design, something else was going to . Others used Manley cranks for quite some time ( buschur,Tscomp) and had a low failure rate. Bunch of 100mm engines which is less material and more leverage.

Point is, you can have the strongest design but if it’s being detonated hard enough something will give. There was a learning curve for this platform for parts and tuning ..

Back to my engine , It’s still running well and a recent oil analysis was clean
. But It’s going to get a full tear down soon with video just to inspect everything.

LetsGetThisDone

iTrader: (1)

Go read SAE white papers. Balance shafts exist for NVH concerns. They do not extend the life of the engine.

Otherwise, how do you explain inline four cylinders that come OEM with no balance shafts that live perfectly long healthy lives? Because all I4 engines produce the same 2nd order vibration that can only be canceled out via balance shafts creating an equal/opposite vibration. So your statements would conclude that the OEM's who decide to not use balance shafts are shortening the the life of their mass produced engines. Which simply isn't true.

RSMike

iTrader: (1)

https://www.jackstransmissions.com/b...balance-shafts