2006EvoIXer

iTrader: (1)

That would be a good poll. You would think the balance shaft belts would last longer than timing belts since it's shorter and doesn't have the same stretching forces as timing belt (crankshaft pulling on exhaust cam which then pulls on intake cam before relaxing until it reaches crankshaft again). If it is replaced with timing belt, it shouldn't be failing if installed correctly.

MinusPrevious

iTrader: (3)

We've been waiting for you to arrive

Can you clarify?

Maybe the distinction is this: A full track EvO w/a built motor would be best served less the BS vs a stock block or mild build that is mostly street driven w/a some track work

In any event, its a good topic of discussion

Biggiesacks

this day and age you would think we could actually get a mitsubishi engineer to weigh in on this, I wonder what forums they are on lol.

ronaldo9

iTrader: (2)

I think its the opposite... smaller belt would mean more revolutions, (faster revolutions?), (more wear?) around the pulley or am i missing something. And consider what these drag racers are revving to. Sometimes north of 9000rpm. That being said I still have my balance shaft with 130k miles and replace them with the timing belt.

barneyb

I've thought this more than once. And, now, since the company has fired the Evo group, someone should be available to talk - but nothing.

Years ago, groups traveling to the shootout made plans to visit the DSM assembly plant at Normal, Illinois. The quality control engineer, their host, was completely in the dark concerning the then ongoing transfercase leak recall - claimed to have never heard a word about it.

2006EvoIXer

iTrader: (1)

Full track evo will have everything modified. Clutch, flywheel, bottom end, etc, so everything will be out of whack. They will want all out power and engine won't last long anyway (something else will fail earlier that will destroy engine before balance shafts will). Imagine everything spinning at or over 9000 rpm (that's 150 crank revolutions per second, imagine that!!!).

As for daily driver, we would give up this additional drag for smoother and balanced engine. The nearest part to BS is crankshaft and flywheel/tranny next. Mitsubishi put this in there to reduce the internal wear. Since these are connected by belt, it is to counter the rotating off-balance. By removing BS, the extra wear on crankshaft bearings would be at the same spot with each rotation and will severely accelerate wear in the high RPMs. We would want to keep it in there as a baseline and with each mod, it will become a little more off balance. Hope this makes sense.

I haven't looked into the physics of how a balance shaft works, but at this time, I think it is to counter the engines' stock vibrations. So each mod will throw this off a little more, but removing it is worst case.

2006EvoIXer

iTrader: (1)

You're right, it can go either way since I don't know the tensions in each belt. Yes, BS belt would rotate faster than timing belt but I don't think the BS resistance is as much as timing belt (small unbalanced rotational mass spinning). The timing belt is pulling on oil pump which isn't balanced, exhaust cam, which isn't balanced either since 2 valve springs are getting compressed each 1/4 revolution (which is 1/2 crank revolution), and then intake cam. Timing belt is wider to take this extra tension. So if Mitsubishi designed it right, both should last 80k to 90k miles and they recommend replacing at 60k.

aurigagt2

Yeah, I once saw a situation where a timing belt tore in half when a broken rod hit a balance shaft, bent it and locked up. I say get rid of them completely, the vibration is only marginally worse.

BluEVOIX

iTrader: (69)

Where did you hear/read that Mitsubishi put the balance shaft for the purpose of reducing internal wear ?

Also it doesn't make sense how removing the BS would result to extra wear on the same spot of the crankshaft bearing ...

2006EvoIXer

iTrader: (1)

This is how I imagination of what happens:
Balance shaft should be designed to minimize vibrations so engine is able to rev up smoothly. Without a balance shaft, let's assume the worst case: engine starts to shake by moving to towards front of car and upward (little hop) at 6000 rpm. During power stroke, engine is pushing down violently (over 2x stock hp). On my evo, crank and rod is rotating downward to front (like pedaling on bicycle). If vibration is opposite to engine power stroke, that bearing contact area will experience extra wear like engine is making more power. Over time, this vibration can accelerate wear on crankshaft bearings and wear a groove. Imagine this occuring at 9000 RPM, which means 150 revolutions per second (wow!).

When people delete the rear balance shaft, do they also delete stock oil pump/front balance shaft too (that's turned by timing belt)?

2006EvoIXer

iTrader: (1)

What about your clutch and tranny gears & spline? Has anyone videoed their engine when on a dyno pull to see how much the vibrations increased? I think most wear would be under WOT and high rpms (6000-8000). The rotational energy of 8000 rpm is not double of 4000 rpm.

Also, do we know if the increased vibrations affect the oiling system? Will oil squirters hit the target areas or will it miss slightly? We just don't know.

Be careful and don't be too quick to undo what Mitsubishi has designed over 20 years. Removing the balance shafts are easy. If you change your mind later, it will be hard to reinstall.

2006EvoIXer

iTrader: (1)

By the way, I'm not here to argue since there is no way we can prove this on either side. I just want you guys to be 100% certain you want this before doing it. As a daily driver, the car vibrates enough already. I can't imagine driving it with more vibrations.

captiveis1

iTrader: (1)

Good discussion everyone! I too would be curious to speak to a mitsu engineer on the reasons for the BS vs no BS debate. I know it’s purpose is to balance vibrations and harmonics, but will its absence increase wear and tear?? It seems most everyone going built motor removes the BS (possibly to lower the risk of grenading a $5k investment). For my purposes I have no reason to argue with the manufacturers decision for a BS, so simply replacing the belt is what I chose to do. And honestly, who knows how long that belt was on there. I bought the car with 64k and it now has 80k. Regardless, I now know to change both the timing and BS belts sooner rather than later. I am just very fortunate I didn’t have to learn the REALLY hard way... lol

captiveis1

iTrader: (1)

Also, I was not aware of how much faster that belt has to spin to do its job... My car is currently making 400whp and sees redline often, I can only imagine the forces acting on it.

2006EvoIXer

iTrader: (1)

The belts don't spin faster than crankshaft. Timing belt is plenty long to probably spin 1/8 the speed. It probably takes 8 full crankshaft turns to get back to same spot on belt. BS belt spins between 1/2 and 1/3 the speed of crankshaft (BS belt rotates about 2 revolutions when crankshaft rotates 3 revolutions). I counted the teeth as best I can but I'll need a printout for better accuracy.





Looking at the gears, the rear balance shaft is probably spins double the speed as the crankshaft (I counted 19 teeth on rear balance shaft sprocket and reached 19 half way through crankshaft sprocket). This makes sense since each BS rotation could be to counter-balance a power stroke. Then looking at the front balance shaft(/oil pump?), I estimate 12 to 13 for front teeth and about 12 to 13 for half way of crankshaft sprocket. How interesting!!!