Balance shaft delete (better MPG observed)
 

I just removed the balance shafts from our 2006 rav4 2.5L and I wish I had done it sooner. The difference is amazing. More power, better response, less throttle needed, and quieter.

It used to down shift on the hills around here and the rpm's would go way up. Now it just rolls right up the hills like they're not even there. Night and day difference.

I hope we don't get a speeding ticket, because it takes barely any throttle to maintain speed. It's going to take some getting used to for sure.

The engine is much quieter now. There was some "clattering" that we attributed to engine wear, but it's gone now. It had to be the shafts making noise. We can now whisper with the engine running, both inside and outside the car. All you hear is the injectors clicking and the exhaust.

The mileage should go up some too.

Do you know the design intent of the balance shaft? Was it for idle vibration?

Yes, it was just for comfort, but you'd have a hard time even knowing it was there.

Such is the case for a lot of modern four cylinder engines... they’re fairly smooth even with the shafts deleted...

Did you physically remove yours or were they powered by their own chain which you could cut/remove?

I took them out. They were gear driven by the crank. They have plastic gears.:eek:

Plastic gears? WtF, Toyota?

I’ll have to buy a kit for my car, my balance shafts are ran on a chain that also runs the water pump...

I know, I was shocked as well.

The engine was making clattering noise and I figured it was just showing age.
It was the shafts! It's sooo quiet now.

Hmm... (looks over ZZP performance catalog)

I'm almost done putting a Honda 2.4L in my Insight. One of my first mods to the engine was to delete the balance shafts. These weight around 11lbs, are part of the oil pump assembly, and spin at twice engine RPM because their purpose is to minimize second order harmonics which would be transferred through the engine mounts. They don't do anything for engine longevity and add both friction and a lot of inertia to the engine.

I'll post a video of it when I'm done, looking like Thursday.

:turtle:

Counter argument:

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

Since balance shafts spin at higher than crank speeds, it makes sense that they can wear out their bearings before the crank bearings, leading to noise etc. So removing worn balance shafts can 'improve' an engine.

Counter argument seems legitimate.

But it states that the problems arise at higher rpms which exomodders never use.

Do most engines have a balance shaft?

A lot of the “modern” designs do... most straight sixes are inherently balanced though, so they may not need balance shafts...

Honda started putting them in their inline 4's which were 2L and greater. I don't think the 1.5L L series have balance shafts but that may not be true for the newer turbo motors.

Again, these shafts do not balance the rotating assembly and are strictly for NVH.

Does the G1 Insight have balance shafts?

Nope!

So how did you deal with the lube system on the balance shaft? Just yanking the shafts ought to leave holes in the bearings and lower oil pressure

Correct. The official unofficial way to do it is to put a bolt or plug in the hole out of the oil pump.

In my engine there's also an extra ~2 quarts of oil capacity afterward, giving you an idea of just how large and heavy these twice-engine-RPM steel shafts are.

I tapped the oil hole for a 1/4x28 grub screw and bottomed it on the cut threads with locktite. It's not coming out without a fight. I am able to use another 1.5-2 qts of oil, which is nice when these engines can burn 1 qt in 1,000 miles. This also helps reduce oil temps.

I will pull the shafts out of my spare motor too, when I go through it.

I need to redo the pistons on the current motor because of oil usage. And the spare will be a drop in replacement to keep the car running.

Results

We have been keeping an eye on mileage since removing the balance shafts and installing the trans cooler to see if there is any change.

Before was ~21-22 mpg After is ~26 mpg over 3 tanks, and one of those tanks was used to haul a 16 ft fishing/ski boat!

That's a big jump!

The balance shafts are gone and that will increase mileage a little, yes, but it's bigger than that. With the shafts gone, the engine has more power available through the entire rpm range. We have noticed that the increased power is keeping the rpm's lower and allowing earlier shifts. This is why there is such a large increase in mileage. It's a cause and effect series. The shafts alone might account for 1-2 mpg, but when the whole system works better, the effects are multiplied.

Less engine drag=better economy, more power available/earlier shifts, less downshifting on hills

All of those things contribute to better economy more than just the reduction of engine drag alone, so it is compounded as it changes how the entire system works.

The whole driving experience is different with the balance shaft delete and trans cooler. It's just a pleasure to drive. There is no need to wind the engine out to 4,5 or even 6k because it has the power down low to do the same thing. Even towing the boat, there was no need to wind it out, it just goes. You couldn't even tell the boat was there at 60 mph. Just amazing. I could definitely tell when I was towing before the mods. The engine worked very hard and would downshift all the time.

The cooler is amazing, and I think it is actually helping to cool the engine coolant with the atf. Temps are ~140 in the pan according to my temp gun.
It feels noticeably smoother with the cooler atf providing more cushion in the transmission and better lubrication. Gear changes are silky smooth, and firm. I like the rav even more after driving it like this. My wife and I have tiffs over who gets to drive it, even if we are both in it at the same time. We need another one, lol.

It feels like a totally different car, period.



Another update:
It was 90* today and we were running errands with the A/C on almost the whole time. The fuel mileage still seems to be doing well.

A lance shafts get removed in race cars too but be warned the extra vibration leads to extra bearing wear which will negate any gains in the long run. Better to just flush the motor by replacing the engine oil with some atf run it for 20 minutes at idle only. drain it replace filter and fill with regular oil. It cleans off any and all deposits that increase friction and decrease mileage. Especially in hydraulic lifter cars.

Bearing wear? The only bearings that were bad were on the balance shafts. That says something. How would a bit more vibration hurt my remaining bearings, especially with increased oil pressure? I'm calling BS on the "more wear from vibration" theory. Diesels vibrate like crazy. My inline truck motor vibrates enough to shake the mirrors at idle. I'm not worried about the tiny amount of vibration hurting the rav. I can barely feel it and nobody else can even tell it's there.

Wrong kind of vibration. I have a Cummins as well and any vibration you are getting there is due to bad mounts not internals. Those engines all run a harmonic dampener which does the same thing as a balance shaft. A balance shaft counters the harmonic vibration of the crank as 4 cylinder engines or aren’t able to equally apply force 360 degrees around the crank thus making them harmonically unbalanced by nature at higher rpms. The larger displacement of a cylinder the more effect that harmonic unbalance will have. Just about every 2.2l 4 cylinder or larger runs a balance shaft. Inline 6 cylinder and above typically don’t need one and only need a harmonic dampener. All that said since a balance shaft is just a counter rotating eccentric shaft or a weight and has little to no power drain so I have to call bs that you noticed any fuel economy difference. Now if you performed the removal in a controlled environment where nothing else on the engine was replaced tans even the same oil was reused then I would be more open minded. Also harmonic vibration engine damage is well documented thanks to years of research from racing.

It takes a certain amount of power to rotate a shaft in bearings. It takes exponentially more to rotate an unbalanced shaft, with the amount of power going up as the shaft imbalance and/or rpm increases.

If I am wrong about the effects on mpg, please tell me where the extra mpg are coming from. :turtle:

Off course it cost energy to drive a balance shaft, but I don't think it's much more than marginal in the end, if the bearings are ok. A balance shaft is in trouble from birth, simply because it's purpose is to cause imbalance to counter act the imbalance made by the pistons and rods. The piston-, rods-, and crankshaft assembly is on the other hand designed to be as smooth as possible, but doesn't make it all the way, hence the balance shaft in some engines. I don't find it strange that the balance shaft bearings may wear out quicker than the others.

The old German Ford V4 ("Cologne engine", used in Taunus and Saab 95/96 of the 1960's and 70's) is very prone to wear out in the balance shaft bearings. You can sometimes get an early warning if having an oil pressure gauge. When the bearings fail, it's not uncommon that the fiber plastic gear goes with them, and that will stop the water pump, the radiator fan and the alternator. That happened to me once, and after the failure the engine was running rough, but more silent, without the whining noise from the alternator. A 60 degree V4 without balance shaft is however way worse in balance than a straight-4.