Balance Shaft Delete Oppopinions

"i86hotdogs" (i86hotdogs) 04/02/2019 at 10:40 • Filed to: None

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Reading deep into threads about Duratec Mazda L engines. Sounds really exciting right? These are in Escapes, Fusions, Mazda 3's and 6's, and the Transit Connect. The aftermarket scene for these are scarce. But I am seeing multiple conversations about removing the balance shaft on this engine to free it up a little bit. The shaft itself is almost 20 pounds; so you’re reducing weight, and letting the engine spin more freely.

This is the underside of a 2.3 Ecoboost

There’s even a removal plug kit to block up the oil feed to the now absent shaft. The reviews are mixed. Some are saying the only downside is the risk of additional NVH (noise, vibration, harshness) at lower RPMs. Others claim you can do catastrophic damage if you don’t re-balance the crank after removing it. Has anyone here done work like this? Any thoughts from the gallery?

M.T. Blake > i86hotdogs 04/02/2019 at 10:50

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Might end up shaking like a can of paint. More annoying than worth it. 

kanadanmajava1 > i86hotdogs 04/02/2019 at 10:53

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The balance shafts only affects to the vibrations coming out from the engine. The engine itself isn’t disturbed by this kind of vibrations but it would cause some vibration sensitive parts to deteriorate a bit earlier (some intake hoses, plastic lines and sensor mountings might start to resonate). But the engine’s internal parts should be fine without the balance shafts.

I don’t know how the system works but the driving gear on the crankshaft could be balanced together with the crankshaft. So removing it might not be a good idea.

CalzoneGolem > i86hotdogs 04/02/2019 at 10:55

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This seems like a bad idea. 

Highlander-Datsuns are Forever > i86hotdogs 04/02/2019 at 11:04

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I have the 2.0 Mazda/ford engine and I wish it had a balance shaft. The 2.0 is very buzzy. But it revs like a scalded monkey.

I would not mess with something like that it could put unnecessary stress on the crank shaft and block assembly.

MM54 > i86hotdogs 04/02/2019 at 11:08

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Should be a good way to, at best, have an engine that performs the same but shakes a but more, and at worst shakes itself to death, especially at lower speeds like you see, you know, actually driving it normally.

jimz > i86hotdogs 04/02/2019 at 11:09

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I wouldn’t. given the weights of the vehicles this engine powers, you’re not really going to get anything out of the reduction in rotating mass. if you were sticking it in something like a tube-frame open-wheel track car, then maybe, but in a 3500 lb Mustang or a 3400 lb FoRS, the vehicle mass is going to dictate how “fast” the engine can rev.

and don’t underestimate the increase in vibration. engines under ~1.6 liters can sometimes get away without them, but driving a big 4-banger w/o counterbalancers will make you question all of the choices you’ve made in life. The reason they’re ubiquitous is not to protect the crankshaft (that’s what harmonic dampers are for) but because of the way the reciprocating assembly works:

in all engines, the pistons move non-sinusoidally which generates harmonic energy. In something like a V6 or V8, the pistons move in different planes and the harmonic energy can be lessened by partial cancellation. But if you look at the 4-cylinder, all of the pistons move in a single plane and in lock-step, reaching TDC/BDC at the same time and reversing direction at the same time. That means the harmonic energy produced by all cylinders sums together  causing an intense 2nd-order vibration (vibration frequency at 2x the crankshaft RPM.)  It’s incredibly irritating and is why 4-cylinders were hated for a long time. 

nermal > i86hotdogs 04/02/2019 at 11:20

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The reduced rotating mass should make the engine rev faster. However, n one of those cars listed would benefit bigly from any small increases in revving speed.

It’s only worth while if you’re doing it because you can, and you DGAF about the engine or the car the engine is installed in. For a legitimate vehicle that you plan to drive regularly, it seems like a bad idea.

HammerheadFistpunch > i86hotdogs 04/02/2019 at 11:24

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Seems like the downsides outweigh the upsides.  The amount of work it would take to tear into the engine to remove the balance shaft could be put to better use elsewhere.  To saying nothing of all that JimZ has said.

Spamfeller Loves Nazi Clicks > i86hotdogs 04/02/2019 at 11:28

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Balance shaft removal requires rebalance of rotating assembly. Anybody saying otherwise is wrong. It affects ALL rotational forces, period , and is also the harmonic balancer. You MUST completely rebalance. Anyone saying otherwise is completely and utterly wrong.

The whole damn point of balance shafts is to offset total vibration in engines which are not inherently balanced and do not have an external damper. That is why it is always crank-driven. This is ESPECIALLY important in inherently unbalanced engines like I4/I6/I8 without an external balancer, because the rotational vibrations have no cancellation  without the balance shafts.

nerd_racing > i86hotdogs 04/02/2019 at 11:42

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Torsional Vibration Damper Design Engineer here!

What balance shafts do: They are an unbalanced shaft that spins at 2x engine speed to create two unbalance vibration pulses per 1 crankshaft rotation. The pulses are opposite in magnitude of the engine’s torsional vibration pulses from the firing order and the slider crank dynamics of the 4 stroke, 4 cylinder engine.

Basically, the inline 4 cylinder is a perfect storm when it comes to stack up of 2nd order harmonics (or 2 events or pulses per revolution). You get slider crank dynamics, on top of firing pulses. The balance shafts allow for much smaller/lighter vibration control devices to be used. So you come in with an undersized vibration dynamic absorber on the free end of the crankshaft, and either a single mass flywheel or a smaller/different rate dual mass flywheel on the opposite end of the crankshaft.

If you delete the balance shafts you will have a higher 2nd order vibration. The tricky part of 2nd order vibrations is that they are low frequency compared to higher order (or higher cylinder count) engine vibrations. This can lead to chassis resonance (lots of noise) or even component resonance and fatigue failures (maybe not a crankshaft, but possibly timing components or even thrown belts).

TL/DR: My opinion would be to consider adding a better quality damper to the free end of the crankshaft if you decide to delete the balance shafts.

Spanfeller is a twat > i86hotdogs 04/02/2019 at 11:44

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Never underestimate vibrations... 

StndIbnz, Drives a MSRT8 > i86hotdogs 04/02/2019 at 12:30

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What JimZ and nerd_racing said.  Having worked on them a bit and looked into building engines without them, if it was designed with it don’t remove it.  To get the same sort of vibration out of the system on a big 4cyl requires a lot of work on the rotating assembly.  Weight out of the rods and pistons and $$$$$.  Also, some BSM’s have the oil pump integrated into the assembly.  Overall, not worth it unless the engine was designed for it.

RPM esq. > i86hotdogs 04/02/2019 at 12:56

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This seems like a bad idea in that it has next to no upside and the downside risk of intolerable NVH and increased vibration-related wear on numerous components.

Longtime Lurker > i86hotdogs 04/02/2019 at 14:44

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I like to point out that the 2.3 duratec in the Rangers and Mazda B2300 come from the factory without balance shaft. 

i86hotdogs > Longtime Lurker 04/02/2019 at 15:06

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You are correct.

tellmewhoareyou > Spamfeller Loves Nazi Clicks 04/04/2019 at 16:09

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Damn. I always thought I6 motors were inherently balanced for some reason.