I am hoping someone can explain the reason the 4G63 has not one but TWO balance shafts.

Balance shafts have been said to add smoothness, as larger-displacement 4-bangers do tend to have quite a large amount of vibration, but in a car as raw as an Evolution, is smoothness really a desirable quality? It is not a luxury car, not by a long shot. Also, I've seen it written that the inclusion of a balance shaft in an engine can be used to cover up imperfections or design flaws by compensating for some imbalance in the engine's rotating mass. In an engine as venerable and as unchanged as the 4G63, I find this 'cover up' argument difficult to swallow as well. What the heck are the balance shafts there for?

The only thing I can think of, looking at the Evo's 4G63 specs, is that the stroke is quite long, larger than the bore. Perhaps this travel causes a level of vibration that is not only undesirable, but unhealthy to the engine if not balanced??? Perhaps Claudius has noticed more vibration since adding the JUN stroker kit if this were true.

Anyone know anything about this? I'm really curious about what the heck these things are for on a car such as the evo.

 

Smoothness is desirable in an engine design because shaking forces can get very large at high rpms. Reducing the vibration will help the moving engine components and their bearings meet expected lifecycles. Less shaking force also means less vibration is transmitted to the passenger cabin, where comfort and perception of quality is usually a high priority.

I don't know why the 4G63 has 2 balance shafts. It could be that 2 are necessary to counteract all the forces and harmonics that the designers felt needed addressing, or that there is 1 balance shaft for each pair of cylinders.

 

The mitsubishi balanced shaft has been around since the 1970's and yes it has two to counteract the rotating parts on both sides of the engine internals. Smooth engines are usually balanced by its design such as V6's and V8 but in line 4's produce a lot of vibrations unlike the V6, V8 and even in line 6's. In fact, Porsche borrowed this balanced shaft design and applied it to their engines. Yes, Mitsu was the original design for the balance shaft.

 

There is a procedure for DSM's to remove the balance shafts (or atleast the rear balance shaft). you can find it on vfaq.com i believe.

To quote them, the balance shaft is for your butt, not neccisarly your engine... it even goes on to say that the 4g63 is well balanced from the factory, but following the procedure if you feel it is neccisary you can balance the engine. the removal of the balance shafts may actually help the engine function smoother...etc... its like removing a dead limb

 

removing the balance shafts also give u more HP to the wheels and add better oil pressure...check RRE site for more info (www.roadraceengineering.com)

 

http://www.vfaq.com/index-main.html They've got the process documented if you're interested (i love this site)

 

beat ya too it... by many days

RRE does sale the "kit" now IDB

 

There is another benefit to removing the balance shafts besides removing the extra rotating mass and getting some HP from it. I've seen plenty of DSM's destroy their motors because the balance shafts wore out the bearings or the balance shaft belt broke taking out the timing belt and destroying the head.

Of course this is more frequent in older cars with higher mileage. If you ever have the motor out of the car pull them!!!

 

Also makes timing belt changes more expensive and 80% of the time shops that aren't familiar with the design screw up the timing, which makes the car run like crap. I've seen them have the balance shaft off by 180 degrees, and the hole car shakes and sounds like it's about to explode.

 

Tell you what..You pull them out and shake your car to pieces. I'll replace the belts at my intervals and run synthetic and stay nice and smooth. If you want to go faster then lose weight. You guys are soo quick to peel something apart that was engineered for a reason.

 

I'd be surprised if you could tell 2 cars apart from vibration, 1 with shafts and 1 without.

And I guess you've never seen motors going because of them, I'm not even talking about the balance shaft belt breaking.

 

i have my balance shafts removed i dont notice a diffrence only thing i know is i dont have to worrie about them locking up in the future i had a 2nd gen and my balance shaft started to make noise and ended up with alot of metal shavings in my oil ..... just like doing head studs or even rod bolts for that extra security and i take my rpms to 8000 and dont notice any vibrations... there point less

 

Why balance shafts? - to sell cars. Mitsubishi used this engine in many other vehicles and you gotta have that smooth test ride in order to sell a car.

So, the question becomes, why'd they not delete them in the Evo engine. Dunno, they should have.

 

The 4G63 is an old engine. The 4B11 doesn't have them. It was to also help balance a non square motor. But I am not an engine designer lol

 

what about in a stroker? would you feel more vibatrions because of "larger mass"?