Reasons to remove balance shafts for race/rally

[vrfour_nz]

I had recently been donated a customers old 1g motor that had come with his rallycar,it had been sitting in the corner of his workshop for a few years after he had seized it on the touring stage of a rally.I stripped it down for a look and this is what I found..one of the balance shaft bearings had seperated and then jammed itself between the crank shaft and main cap.The other had spun the bearing in the block and actually unwound down the front balance shaft..There was nothing supporting either balance shafts.Apparently it had got a vibration then lost power like the cam timing was out,before seizing. /ubbthreads/images/graemlins/devil.gif

 

[Andy_S]

Less rotating mass for quicker revs. The biggest thing for me though is the reliability. You don't have to worry about the balance shaft belts breaking and timing belt jobs are much easier when they are out of there.

 

[ktmrider]

Probably the most common mod to the internal engine on the 4g63 around ( BS delete ).
That bearing wedge is kinda new to me but after sooooo many tossed BS belts, knarled t-belts, and subsequent munched valvetrain removing them seems to be a good idea.
I would think a decently balanced rotating assembly plus quality harmonic balancer would be more fairly vibration free.....

 

[gtluke]

I really need to take mine out. I've been meaning to do that for 8 years now

 

[jepherz]

I bought a car that had sat for over 5 years recently. On the road to revival, I did the water pump and timing belt. Just to get it running, I didn't mess with balance shafts at all so I installed both belts. With the belts off, the front balance shaft spun fine by hand, but after I put the motor all together and started it, all of the teeth instantly ripped off the balance shaft belt. I re-assembled it with just that belt removed for now, but I will probably do the full delete this winter.

 

[atc250r]

Both BS bearing failures I've seen have been the "spit the bearing out the bore" type.

John

 

[H05TYL]

I keep hearing that they are "un-neccesary if you have a fully balanced built engine"

Which whilst technically correct, is misleading. They are actually "un-neccessary" in a stock application, in that, they are not fitted because mitsi didn't bother to balance the rotating assembly of the engine.

Mitsi used balance shafts to cancel out much of the vibration that comes with an inline 4cylinder setup, to increase smoothness of the engine, comfort for the passengers and reduce nvh.

 

[atc250r]

Absolutely. When I went to Mitsu factory training as a tech the instructors basically said "the balance shafts are there for your butt, not the engine". Balancing the engine does little if anything to prevent the harmonics that are unavoidable in a n I-4 engine.

John

 

[ktmrider]

^^ Makes sense fellas, I always heard the 6 cylinder combo is inherently ideal due to naturally cancelling harmonics.