Quoting GSTwithPSI:
My GST has the stock motor with around 160k on it. It is my daily driver and it is lightly modded
click . I have never had any issues with the balance shafts themselves, only with the balance shaft belt. To me, the balance shaft belt is the weakest link in regards to balance shafts. Much of the time when the balance shaft belt goes, it can take the timing belt with it.
They absolutely do make a difference with how smooth the motor feels though. It is probably up to each individual how much of a difference this is and how it is perceived, but it would be wrong to say the don't make the engine operation smoother and reduce vibrations some. It could be argued that the difference balance shafts make are negligible, especially depending on how your car is modded, but there's a difference none the less. I would say the reasons to eliminate them far outweigh the reasons to keep them, but I like the smoothness they provide on my current setup, and have opted not to eliminate them.
I will end with a story. I was driving my GST a few years ago when the engine all of a sudden started feeling like it was running rough. It wasn't all the time, but while accelerating through the gears I could definitely feel a vibration which randomly got better and worse through the RPM range. I started to troubleshoot for all sorts of problems. At idle the car hardly seemed different, but as soon as you would rev the engine there was no doubt something was broken and it was running rougher than before. The worst thing was the car ran great still, it just vibrated and felt like sh*t. It felt like a misfire almost, but the car ran too good for that to be the case. After tons of work and troubleshooting, I finally figured out the vibration was caused by a bad balance shaft belt. The timing gears had cleaned all the teeth off the belt, and it was just chillin under the timing cover not doing anything. Luckily it didn't break off and destroy my timing belt. I replaced both belts and called it a day. I tell you this story only to point out, that I could instantly feel the difference in the car without the balance shafts in action. It felt foreign, and without the shafts doing what I was used to them doing, the car felt like crap. I would have never thought they would have made such a difference had this not happened to me. Since that happened, I've always like the idea of keeping them because of the smooth operation they provide. Just my 2 cents.
This is actually misinformation. The reason your car vibrated harshly and felt like sh*t, as you described it, is because you had ONE balance shaft still rotating with the weight spinning.
"Balance shafts are commonly found in inline four cylinder engines such as the Mitsubishi 4G63 which, due to the asymmetry of their design, have an inherent second order vibration (vibrating at twice the engine RPM) which, contrary to popular belief, cannot be eliminated no matter how well the internal components are balanced. This vibration is generated because the movement of the connecting rods in an inline engine is not symmetrical throughout the crankshaft rotation; thus during a given period of crankshaft rotation, the descending and ascending pistons are not always completely opposed in their acceleration, giving rise to a net vertical inertial force twice in each revolution whose intensity increases quadratically with RPM, no matter how closely the components are matched for weight."
This is a quote from someone much smarter than me. Having built several engines though, I understand it and the very small side effect of removing the balance compared to the risk you take of leaving them in. The balance shafts rotate at twice the speed of the engine and yet rely on bearings smaller than either the rod or main bearings. In theory, with good oil pressure, this wouldn't be a problem. But the belt being smaller is a weak link and the tendency for oil pressure to "momentarily" be a little on the low side effects these more than the rods and mains.
I won't build an engine without removing them. The absolutely minimal noticeable vibration is far outweighed by the piece of mind gained from there absence.
Josh
