I'm curious what decel in gear does to the bearings? Is this something that should be avoided?

 

The concern is doing it at the end of a quarter mile (or 1/2 mile) pass where the pan is already partially drained from just having spent the back half of the track in 4th gear (5th gear in the case of doing 1/2 mile) at high rpm, then you slam on the brakes and all the oil goes forward and away from the pick up, starving the motor. Popping it out of gear lets the engine idle, greatly reducing the chance of damage from low oil pressure.

 

Thanks for comments guys. I'm stuck on jury duty until end of month. I will update whole write up to only focus on balance shafts so this thread can have some value for future searches. Feel free to keep commenting until I can clean this up.

 

The only value is - You should delete your balance shafts...lol. With supporting evidence...

 

@JohnBradley can you confirm this? I didn't know you where a mech. engineer, I don't see you registered in the state of WA. Always happy to meet engineers on here.

 

That's not my style. I give people the logic and background info for readers to decide for themselves. I'd rather explain the logic so people can understand the risks (if any) behind their decision.

 

The only evidence I've seen in this thread is engine builders stating they haven't had problems deleting them. I don't think that's enough to completely discredit why Mitsubishi and many other OEMs put them in. I would really love to see some actual engineers knowledge on how they work rather than assumptions and anecdotal experience.

 

100's upon 100's of engines isn't anecdotal. None of us are assuming how they work, plenty of info on the web on that, and it's a pretty simple concept- you have frequency A that you wanted cancel out, so you make some parts to creat frequency B, which is the same as A but 180* out of phase and they cancel each other out. Its simple physics. You want to hear why mitsu installed them, but don't seem to care that many other I4's never came with them. And if it's an I4 with a flat crank (which they all are), they all make these second order vibrations that mitsu aimed to cancel out by installing balance shafts. The 4g3 isn't special with some special vibration that wiped out motors and mitsu deemed it needed bshafts.

You haven't presented a case for keeping balance shafts. Only theories which have largely been shown to not be correct.

 

Mitsubishi put them in to reduce NVH.

 

100's upon 100's of engines with no actual study done as to whether any wear they experienced was accelerated due to BS removal. If you're not looking, you won't find anything. There actually really isn't much info on the web aside from what you just posted, no studies on BS and internal component life, etc. That's what we're trying to gain from this thread. Some actual data, not just I've built 1000 engines without a BS and we haven't noticed an issue. You keep saying that many OEMs did not use them in their i4s, and yet a ton of OEs did use balance shafts in their engines. Honda alone ran them in the K20, K24, F22, and H22 engines. Tons of these engines where built, think about how much money they would have saved if they didn't bother with it. Is it that unreasonable to think an OE wouldn't save that money if they could? Especially with the corporate bean counters on their backs. That is what's driving this question, why do so many OEMs use a seemingly(as you claim) useless component in their factory builds?

 

I haven't seen any actual data to suggest that this is the only reason they exist. Do you have any info that backs up that claim? I've been hearing it a lot, but I can't find any concrete evidence, and balance shafts for the sake of NVH seems like an unusually complex solution to a simple problem(NVH).

 

i think the obvious reason that mitsubishi and others installed balance shafts is because they assume people wont buy cars with the levels of NVH that higher displacement I4 engines produce.

 

I am not going to write a white paper on why to delete them. If I wanted to do that I would also write a story about how Kraft Cheese paid to send astronauts to the moon for mining research.

I am also not registered as an Engineer in the state of WA, I graduated and never used my degree in the field. I use what I learned at work which isnt the same thing but I digress.

I think its really simple, some people feel they are going to rediscover some lost knowledge. Next it will be reinstalling EGRs on to intake manifolds. After that I foresee catalytic converters making a trendy comeback. If you want a belt driven shaft turning twice engine speed (so in some cases 16000rpm or more) be my guest. When it seizes and wads the belt into the timing belt hopefully it doesnt kill anything other than a crank sensor.

 

Well said & my thoughts exactly. Im not a degreed Eng but i work w/them daily & involved in the mechanical industry

 

Because bshafts are the only complete solution to this particular NVH issue. There is no other way to resolve these second order vibrations. It's really not complex to make them if you know the math and have the equipment.

Why do OEMs spend all the money to develop rubber mounts when they could just solid mount the motor and other drivetrain components to save a bunch of money?

Honda B and D series don't use them, plenty of those running around with a billion miles. Nissan KA and SR don't use them and again plenty of these running around also. Not like there was a yuge wide spread issues with these engines eating bearings or breaking **** in an abnormally short time.