Cutting the balance shaft?

[_97tsiawd_]

Ok so I was getting ready to get a stub sahft to install, then I read on DSM.org to just tap the the shaft for a 25mm bolt to seal the oil holes and CUT the rear shaft off. Is this something I should do? Is it going to hurt anything?



Edit: Its a 6bolt block.

 

[dsm-onster]

Canceling engine vibrations is always a good thing, even today.



Gear size has no effect on second order harmonic imbalance.



But yes the horizontal forces from one eccentric shaft do cancel the horizontal forces of the other. When the off-center weight on one shaft is pointing left, the other is pointing right. When the forces from the two shafts are horizontal, the two forces are equal and opposite, canceling each other.

One rotating bs does not cancel the individual vibrations seen by the other BS bearings. Neither does it negate a vibration in a crank. The bs assemblies cancel the sum of vibrations that would otherwize be felt from the block. Relibility is not compromised by removing any bs.

The premise is: since we have one vibrating assembly (crank), lets add another (bs assemblies) so that the block stays still. All of the individual assemblies still vibrate and do as much damage to the bearings as they would individually, but the waves are cancelled by the time they reach the block surfaces.

The properties of the rubber belt play no part in balancing the engine, it just drives one shaft.



Yes one is as "wobbly" as the other. But the effect of the system consisting of the engine and both balance shafts is affected by phasing. As designed, both shafts have upward forces that are additive when the engine's second order harmonic forces are downward. Both shafts have downward forces that are additive when the engine's second order harmonic forces are upward. Because the shafts rotate in opposite directions their left and right forces cancel each others.

If the shafts are both 180 degrees out of phase they would add to the engines natural vibrations. If they both rotated the same direction their horizontal forces would be additive.

With only one shaft, it will add horizontal vibrations to the engine whether in phase or not. This is the point that was intended to answer the OPs post.



No, the purpose of the balance shafts is to cancel the second order harmonics that are inherent with four cylinder in-line engines. In-line fours like the 4G63 engine have two pairs of pistons 180 degrees apart on the crankshaft. One pair goes up while the other pair goes down. If the speeds and acceleration rates of the two pairs of pistons were the same, the engine would be perfectly balanced. However, because the rod angle changes, the velocity of the piston changes throughout the stroke. With any reasonable rod length the piston velocity is higher near TDC than at BDC.

Please see Balance shaft - Wikipedia, the free encyclopedia for the Wikipedia article on balance shafts.



Actually that link was to my post in the FAQ that discussed the effect of balance shafts out of phase or missing.


I know I'm an annoying old man but not old enough to discuss my arse in a public forum.

In my stroker Talon most of the vibrations seem to go the steering wheel.



We agree that the balance shafts are eccentric, maybe that's why I like them.




Good point. This is the essence of the 1977 Mitsubishi patent on balance shafts. (
Engine balancer - United States Patent 4,028,963) That Mitsubishi patent called for a bearing on each side of the eccentric weight instead of being cantilevered in order to decrease the wear on the balance shaft bearings. Those bearings are heavily loaded due to the imbalance of the shafts. The main bearings on my Talon were "like new" after 183,000 miles bathed in Mobile One while the balance shaft bearings were in bad condition.



The crankshaft can/should be balanced by adjusting the counter-weights for static balance. Static being the key word. An in-line four cannot be statically balanced to eliminate second order harmonics.



This bit of lore has been promoted to myth. When I started the calculations for the StrokeOrNot document I expected to find that the vibration forces from mismatched piston weights would be much more than the forces from second order harmonics. Boy was I wrong. The imbalance forces exerted on the crankshaft from second order harmonics is about ten times the force on the crankshaft from pistons that are mismatched by 20 grams.

I still hold my olde cherished belief that piston weights in a performance engine should be matched. Closely matched. But now that I know that second order harmonics are applied to the crank in the same manner as static imbalance, and are ten times as great, I have to re-think just ignoring the harmonic imbalance.



[sarc on]I know something about being unbalanced but have never been very good about keeping still. Oh, you mean the balance shafts? [/sarc off] The concept of balance shafts in four cylinder engines is over 100 years old. It's a real consideration is basic engine technology.

If static balance is important to keep from vibrating the valve train then I just can't ignore the effect of second order harmonic vibrations on the valve train. The balance shaft loads are coupled to the block. The vibrations from the second order harmonics are coupled to the block. With the balance shafts in place the block will vibrate less.

That was a lot of words for a single post. Please see http://www.kidzuku.com/StrokeOrNot.pdf for even more words and pretty charts on this topic.

HAHA! Ok. . . the op is wondering if cutting off the bs will damage any engine component. The answer is no. The bs cancels vibrations that the block has (vibrations which transfer to the unibody). The link you posted vouches for that. It does not cancel out vibrations in the crank shaft itself. Only as the vibrations leave the shaft and enter the block does the bs system cancel it out at that point. Removing one shaft and leaving the other in rotation or running them out of phase does not increase the likelyhood of damage to the BS bearings, main bearings, rod bearings, oil pump. Or any other block component. I suppose that is what you are saying .

Yes, vibrations are coupled to the block. But nothing can prevent damage but a balanced crank. Nothing can damage due to vibration but an unbalanced crank or broken dampener. A dampener is affixed to the crank to save it from itself. Balance shafts do not assist in this proccess.

 

[_97tsiawd_]

Alright guys, thanks. I cut and put everything back to gether so its too late to change now

 

[TerribleTSi]

just to ask, is there a real performance increase from the BSE. i've heard it revs quicker and in the ballpark of a 9 horse power gain......is this so. i'm taking them both out this week and was wondering ifi'm gonna come back with a lower ET

 

[TunaTalon]

One rotating bs does not cancel the individual vibrations seen by the other BS bearings. Neither does it negate a vibration in a crank.

Those carefully chosen words are correct. The loads on the bearings of one BS are unaffected by the other BS. However it is still true that the horizontal vibrations of the block caused by one BS are canceled by the other BS.

The bs assemblies cancel the sum of vibrations that would otherwize be felt from the block.

If “the “sum of vibrations” can be read as “forces due to second order harmonic imbalance” then this is correct. There are of course many other sources of vibration that are unaffected by the BS assembly.

The premise is: since we have one vibrating assembly (crank), lets add another (bs assemblies) so that the block stays still. All of the individual assemblies still vibrate and do as much damage to the bearings as they would individually, but the waves are cancelled by the time they reach the block surfaces.

The premise of canceling second order harmonic vibrations with balance shafts per Mitsubishi Patent number 4,028,963 is familiar to me and well documented in the literature. My personal favorite explanation of the premise is by Ford at 2.3 DOHC Overview

HAHA! Ok. . . the op is wondering if cutting off the bs will damage any engine component. The answer is no. The bs cancels vibrations that the block has (vibrations which transfer to the unibody). The link you posted vouches for that. It does not cancel out vibrations in the crank shaft itself. Only as the vibrations leave the shaft and enter the block does the bs system cancel it out at that point. Removing one shaft and leaving the other in rotation or running them out of phase does not increase the likelyhood of damage to the BS bearings, main bearings, rod bearings, oil pump. Or any other block component. I suppose that is what you are saying .

Again those carefully chosen words limiting potential damage to the bearings of the crank and the BS assembly are correct. If we ignore the potential damage that engine vibrations can cause to other components then the BS assembly is pretty worthless. [sarc on] Of course if we ignore the potential damage of overheating the engine then the radiator is pretty worthless too. [/sarc off]

Yes, vibrations are coupled to the block. But nothing can prevent damage but a balanced crank. Nothing can damage due to vibration but an unbalanced crank or broken dampener. A dampener is affixed to the crank to save it from itself. Balance shafts do not assist in this proccess.

It is agreed that the BS assemblies do not protect the main bearings. However, I do not agree that the BS assemblies do not protect other parts attached to the engine.

Outside of the DSM world, the performance community considers engine vibration to be an unmitigated evil. Vibration in a performance engine is usually described as something that will shake the engine to pieces. Some proponents of balancing such as overbore (Engine Balance - Resource - Overbore) describe how vibration can damage such components as oil pumps, harmonic dampeners, and motor mounts. I found no mention of hard numbers in the literature such as G forces or peak to peak excursions. Vibration in engines seems to still be handled like the mantra from my first hot rod:
Beer good, vibration bad.

What’s missing from the literature is the magnitude of the second order harmonic vibrations. After reading forums and articles like the Ford Scorpio site I had the impression that vibrations from second order harmonic imbalance are much less than from an imbalance due to mismatched piston weights. While drafting the StrokeOrNot document I had a bad case of scope creep and made the calculations myself. To my surprise the magnitude of the second order harmonic vibrations are 32 times the magnitude of a 10g mismatch between pistons. See Figures 19 and 20 of StrokeOrNot.pdf (http://www.kidzuku.com/StrokeOrNot.pdf) for forces in pounds at 8000 RPM.

Relibility is not compromised by removing any bs.

So then, if some young impressionable DSM owner says he scored some super strong main bearings made from unobtainium at a swap meet along with a pair of Mahle pistons at 250g each and wants to keep a pair of his stock pistons at 405g each, he isn’t worried about the new mains but wants to know if the vibrations from the mismatched piston weights will harm his oil pump, harmonic damper, and motor mounts. Would you feel comfortable with telling him to put the Mahle pistons in cylinders two and three and leave the stockers in one and four? That would only result in one half of the vibrations from removing the balance shafts.

I have double checked the math and intuitively compared the shape and weight of the balance shafts to $7.00 worth of dimes and can’t find any errors in analysis or judgment. If someone can find an error in the math I will re-consider my position on vibrations. Just don’t challenge my belief that beer is good.

 

[dsm-onster]

Regardless of how you view vibrations , I still rev to 8500 rpms, and over 9K on occasion. With one BS rotating and the other stationary. There is no wild vibrations. When others with BS removed destroy enginebay components from vibrations, I'm sure they will report back. The BS mod article has been in the vfaqs since 1998, there should be a flood of failures pending .

So then, if some young impressionable DSM owner says he scored some super strong main bearings made from unobtainium at a swap meet along with a pair of Mahle pistons at 250g each and wants to keep a pair of his stock pistons at 405g each, he isn't worried about the new mains but wants to know if the vibrations from the mismatched piston weights will harm his oil pump, harmonic damper, and motor mounts. Would you feel comfortable with telling him to put the Mahle pistons in cylinders two and three and leave the stockers in one and four? That would only result in one half of the vibrations from removing the balance shafts.

Mismatching weights affixed to the crank will damage the crank.

Cutting the bs belt and or removing the bs assembly has demonstrated no affect on durability in the hstory of the DSM. No one installes parts so loosely that the vibrations from a non-bs engine can damage.

Have another beer.

 

[TunaTalon]

Regardless of how you view vibrations , I still rev to 8500 rpms, and over 9K on occasion. With one BS rotating and the other stationary. There is no wild vibrations. When others with BS removed destroy enginebay components from vibrations, I'm sure they will report back. The BS mod article has been in the vfaqs since 1998, there should be a flood of failures pending .

Maybe the failures are no longer pending. In my short time on DSMtuners I have noticed many threads about failures of motor mounts and harmonic dampeners.

Cutting the bs belt and or removing the bs assembly has demonstrated no affect on durability in the hstory of the DSM. No one installes parts so loosely that the vibrations from a non-bs engine can damage.

So we leave this thread with the conventional wisdom in the DSM community in conflict with conventional wisdom in the rest of the performance world; and the anecdotal evidence in conflict with mathematical analysis.

Have another beer.

Ah, now that's a better way to end this thread. Yes sir and you keep a close watch on your crank pulley.

 

[dsm-onster]

You must be logged in to view this image or video.

Been doing it for years.

 

[TunaTalon]

Oh, and in case you have an automatic keep a close eye on the A/T pump. That's one of the components at risk from vibration according to Overbore. (Engine Balance - Resource - Overbore)

Cough, cough, http://www.dsmtuners.com/forums/automatic-tranny/278626-how-remove-t-pump.html#post151364984 cough.

 

[dsm-onster]

Oh, and in case you have an automatic keep a close eye on the A/T pump. That's one of the components at risk from vibration according to Overbore. (Engine Balance - Resource - Overbore)

Cough, cough, http://www.dsmtuners.com/forums/automatic-tranny/278626-how-remove-t-pump.html#post151364984 cough.

Wow, we bought that car w/ no balance belt installed. And the pump/tranny was shifting excellently . I broke the gear in the pump when I was drawing the tranny to the block with the bellhousing bolts. . . a big no-no.

Overbore mentions nothing about rotating assemblies not connected to the crank like balance shafts. Overbore does discuss balancing pistons, cranks, rods, dampers flywheels, and pressureplates. There is no discussion that adding other wobbling mechanisms affect reliability.

The discussion of the oil pump is a "can happen" discussion. Where oil pumps are affixed to an unbalanced crank itself, like a subaru 2.5L. The tranny pump is connected to the crank itself via the liquid coupling of the torque converter.

BTW, our oil pumps are affixed to a permanantly wobbling shaft, the rear balance shaft. The crank rotating assembly and the other bs cancel the vibrations seen in the block, but not the vibrations in that rear balance/oil-pump shaft.

 

[BUCK]

I plan on leaving the front shaft in with no belt. Either way, kit or no kit. I've got the motor pulled now and doing a slight rebuild.

I left Front in as I was doing BSE IN CAR - Just used new Seal up Front & Stubby Shaft at Rear, NO problems - With Motor OUT like you have I'd go the "full monty".

 

[PieEyedPiper]

Bringin' her back..

I'm going to be doing a full timing job coming up, and I intend to at least test it out with just a cut balance shaft belt before I really dig in. I planned on replacing the balance shaft belt, and I probably still will do that, but I have to taste this debate for myself.

Has anyone had any recent experiences with this? Regardless, I'll post up my anecdotal experiences after a test drive.