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balance shaft removal

paul j

Well-known member
Joined
Apr 27, 2004
Messages
282
Location
Lone Tree, CO
Biglady112 is helping me put 1551 engine back together. I had planned on keeping balance shafts, Steven suggests removing balance shafts. This is not a racer but an almost stock daily driver. Pros and cons anybody?
 

GSTwithPSI

Well-known member
Joined
Jan 1, 2012
Messages
3,460
Location
SoCal
In short, no, you don't need them.

Quoting slugsgomoo:


it's the one place that I will categorically say that Jack's is wrong, and I think they're great otherwise.

Fact: Mitsubishi built dozens of 4gxx motors that came from the factory without balance shafts. If the motor can't live without them, wouldn't Mitsubishi's engineers be able to figure that out? Let's assume that some of them have a Masters in Mechanical Engineering (or better) and have an idea how torsional & harmonic damping work

Fact: The documentation from Mitsubishi says that the shafts are there to increase occupant comfort by reducing felt vibration from ~3-5k RPM. Felt vibration means your ass is happy, it has nothing to do with the mechanicals.

Fact: Even if replaced regularly, the balance shaft belt is very small, and spins a very heavy weight.

Fact: If you start pushing past factory 7,500rpm limit with balance shafts, you're retarded

Fact: for every revolution the crankshaft makes, the balance shaft makes two. This means that at the pedestrian limiter of 7,500, your balance shaft is spinning 15,000 RPM. If you push out to 8500, it goes to 17,000. I'm spinning to 9,500 RPM, or 19,000 RPM on a balance shaft, on a belt about the size of a power steering belt. This teeny belt has the ability to catastrophically self destruct, taking out very expensive engine parts.

I didn't have clutch drag with an ACT2600 in 2005 with a stock motor, or with a built 9:1 motor with no balance shafts (Same clutch, same shitty transmission). I don't have clutch drag now with a twin disk, aluminum rod motor, and no balance shafts.

I'm not a Buschur fan, but LOL @ click

Also has some decent insight here click posts 6 & 7 seem relevant, but the whole thread, and jack's replies are worth reading.

I should add as a further case in point, the 4G61 does not have balance shafts from the factory. In fact, the proper parts to use for a BS delete come from Mitsubishi's parts catalog as OEM parts for the 4G61...

Realistically, this was ancient news when I got into DSM's in 2002...

vfaq - balance shafts


 
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