Balance shafts, should they stay or should they go?

[Snail Tuning]

ok my 1990 TSI AWD is up for a timingbelt change. (theres a crack in the belt) so ive stopped driving it, and im going to be changing the belt, waterpump, and possibly the balance shaft belt aswell. my question is. Should i buy the removal kit and get rid of them, or can i just use the oem timingbelt kit from prostreetonline, and just do the standard belt change. car has 147k on it, and is running strong.

 

[mitdrx]

Whether or not you should remove them depends on how much you care about a few more horsepower. They do smooth out the motor. But at the same time rob you of a few horses. Quite a few cars are running them removed.

 

[TurboChrged93]

Actually, proper... PROPER removal of the balance shafts ... you should have everything rebalanced. Your taking out something that is vital and is in there for a purpose. I have seen guys remove the balance shafts smoothly, no problems, and they love it. But I have also seen it cause the engines to shake alot more than with them untouched. I've had/have 3 dsms and always left them in. Never had a problem. And worry about bigger, better mods. Also removing the balance shaft while the engine is still in the car is another task. It's not fun, and is it rewarding?

My final answer and opinion. Leave it be.

 

[rgurleyjr81]

I may get flamed for this but in my opinion, I would just remove the BS belt and leave them in. I did a BS removal with the engine in the car and it was a mess!!! I couldn't get one of the BS bearings out to install the BS blockoff bearing so I had a loss of oil pressure. Rather than you go through that OR have to worry about a bs belt snapping causing a failed head, just take the belt out.

 

[Defiant]

Actually, proper... PROPER removal of the balance shafts ... you should have everything rebalanced.

Um... no. The Silent Shafts have nothing to do with the balance of the bottom end. They're only to counter a 4-cylinder's inherent second-order imbalance, which is the weight of the bottom end as it tries to throw the motor side-to-side (back-and-forth as mounted in a DSM) as the big ends are around the halfway point of the piston stroke. It's a completely different phenomenon from the balancing of the reciprocating and rotating assemblies.

I like balance shafts, and doubt their loading on the engine is significant. Of course, anything that moves can go wrong, so pulling them obviates that.... much in the way that removing your testes will eliminate the threat of testicular cancer.

 

[JCMDSM]

^^ haha funny comparison. Most people who remove them remove them to avoid the possiblilty of the BS belt breaking and then gettin cought in the timing belt and breaking it. I am removing mine because the engine is out for a rebuild anyway. So long as you maintain the parts of the BS (mainly the belt) system it should do ok left in. If you are anal about your engine like me you'll pull them out. Either way should do fine.

 

[94awdcoupe]

http://en.wikipedia.org/wiki/Balance_shaft

Balance shafts are most common in inline four cylinder (straight-4) engines 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 pistons 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 exponentially with RPM, no matter how closely the components are matched for weight. See the 0 degree cylinder angle, 180 degree crankshaft angle animated example here for a very clear depiction of this sometimes hard to visualize vibration (as well as the mathematical equation which describes it).

The problem increases with larger engine displacement, since the only ways to achieve larger displacement are with a longer piston stroke, increasing the difference in acceleration, or by a larger bore, increasing the mass of the pistons; either way, the magnitude of the inertial vibration increases. For many years, two litres was viewed as the 'unofficial' displacement limit for a production inline four cylinder engine with acceptable NVH characteristics. The development of the General Motors 2.3 litre Quad 4 engine in 1987, described as "rough as a cob" by one automotive reviewer, and its subsequent development into the much more positively received 2.4 litre version with balance shafts confirms the wisdom of this assessment.

The basic concept behind balance shafts has existed for nearly a century and is no longer patentable. Two balance shafts rotate in opposite directions at twice engine speed. Equally sized eccentric weights on these shafts are sized and phased so that the inertial reaction to their counter-rotation cancels out in the horizontal plane, but adds in the vertical plane, giving a net force equal to but 180 degrees out of phase with the undesired second-order vibration of the basic engine, thereby canceling it. (Some motorcycle enthusiasts believe that Honda's original application of this technology to their V-twin motorcycle engine overly damped out the vibration, giving an excessively 'dead' feel, so that they later reduced the size of the balance shafts in order to furnish the rider with some feedback as to engine speed).

The actual implementation of the concept, however, is concrete enough to be patented. The basic problem presented by the concept is adequately supporting and lubricating a part rotating at twice engine speed, at the higher RPMs where the second order vibration becomes unacceptable. Mitsubishi Motors pioneered the design in the modern era with its "Silent Shaft" Astron engines in 1975, with balance shafts located low on the side of the engine block, driven by chains from the oil pump, and subsequently licensed the patent to Porsche, then to other manufacturers. Since then, other manufacturers have adapted the same basic layout to their needs.

Saab has further refined the balance shaft principle to overcome second harmonic sideways vibrations (due to the same basic asymmetry in engine design, but much smaller in magnitude) by locating the balance shafts with lateral symmetry but at different heights above the crankshaft, thereby introducing a torque which counteracts the sideways vibrations at double engine RPM, resulting in an exceptionally smooth four cylinder engine.

There is some debate as to how much power the twin balance shafts cost the engine. The basic figure given is usually around 15 horsepower (11 kW), but this seems excessive for pure friction losses. It is likely that this is a miscalculation derived from the common use of an inertial dynamometer, which calculates power from angular acceleration rather than actual measurement of steady state torque. The 15 horsepower (11 kW), then, includes both the actual frictional loss as well as the increase in angular inertia of the rapidly rotating shafts, which would not be a factor at steady speed. Nevertheless, many owners modify their engines by removing the balance shafts, both to reclaim some of this power, but also to reduce complexity and potential areas of breakage for high performance and racing use. As mentioned above, it is commonly believed that the smoothness provided by the balance shafts can be attained after their removal by careful balancing of the reciprocating components of the engine, but that stems from a basic misunderstanding of their operation.

here you go. read up!

 

[Snail Tuning]

thanks for the quick reply's i was hoping i could leave them in and just change the belt with no problems. but as i was reading through some parts sites they listed some problems with leaving the shafts in, and i wanted to make sure they weren;t ganna break or something. im going to leave them in because its ganna be alot less work, and if everything looks good when i pull the belts off, ill just put the new belts on change the waterpump and t/belt tenioner, and call it a day.

thanks for the help

 

[Defiant]

Well, crap. Didn't take me all that space to say the same thing.

 

[HighPsi92GST]

I say get rid of them. I have seen/had to many engines wiped out by the balance belt breaking and falling into the timing belt.

 

[Quasimondo]

I may get flamed for this but in my opinion, I would just remove the BS belt and leave them in. I did a BS removal with the engine in the car and it was a mess!!! I couldn't get one of the BS bearings out to install the BS blockoff bearing so I had a loss of oil pressure. Rather than you go through that OR have to worry about a bs belt snapping causing a failed head, just take the belt out.

You can't just pull the belt. That's fine for the front shaft, but the rear shaft is driven by the oil pump and must be removed. Otherwise, you'll have engine vibrations at 3-4K that's worse than if you had no balance shafts at all.

I'd keep them in. Not because it's not worth pulling, but because it's a bi*** to get that rear shaft out unless you have something to cut the shaft in half with or you're pulling the engine out. If you're rebuilding your engine, remove them by all means, but if you're just doing timing belt maintenance, it's not that much more effort to get to the balance shaft belt.

 

[2-0turbo]

I lost my first engine from a failed BS bearing. It is not always just the failed belt that contributes to a loss. If you look a the very detailed write-ups included above, you see that the BSs rotate at 2X engine speed. If you rev to 7500 RPM, that is 15,000 RPM for a journal type bearing. That is very fast and if you look at the surface feet per minute, you will find it is marginally acceptable for long life.

I chose to get rid of mine during my rebuild. I have no regrets. Idle is a little rougher, but you don't notice it at all during cruise. And I like the fact that I've gotten rid of 6 lbs rotating mass from my engine and made timing belt jobs SSOOOOO much easier.

 

[Turbo Talon DL]

Take them out. BUT, only if you can do it correctly. I like the throttle response of my fully balanced/blueprinted motor without the BS. Only thing, my oil pressure is so high now

 

[tonygst]

Well, crap. Didn't take me all that space to say the same thing.

!
i was going to say the exact same thing

 

[gamiller31]

Trubo Talon,
Is much higher oil pressure a result of removeing the balance shafts?