gmanuel

I have seen a number of posts for this question in one form or another. Has changin ghe balancer corrected you problem? Please list your problems and what changes did the replacement balancer have?

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83Z28, 350,5speed,TTops,Heddman Shorties, mild cam, K&N air filter.

Vader

GM,

On the simpler side, a failed harmonic balancer can be one that has had the outer ring slip out of position, making the task of adjusting base ignition timing very difficult. Since there are no crankshaft position sensors on our cars (at least not stock) there are no other really negative effects unless the outer ring is loose or cracked.

On the more complex side, if the elastomer ring has hardened, distended, split, or disintegrated, the balancer may no longer be able to perform its main function effectively. That is to say that the harmonics created in the crankshaft may no longer be effectively cancelled by the floating rubber and iron ring.

I'll admit that I'm not that strong in mechanical physics, but what little I do know I have tried to apply to the engine design to try to determine the resonant frequency of the typical SBC cast crankshaft. Since I don't have the equipment necessary to measure the harmonics of the crank assembly in a running engine, I've only been able to theorize. There are so many variable in the equation that determining an exact resonance point is almost impossible. Combustion points and rates, compression, mass of rods and pistons, load, bearing clearances, and even internal friction all skew what would otherwise be a pretty straightforward calculation. Use a steel or billet crank with trimmed counterweights, and the numbers all go out the window due to different molecular elasticity and rotating centers of mass.

In a nutshell, the harmonic points of the typical 350 SBC cast assembly in stock form seems to be at multiples of 1,700 RPM. Again, this is by my rough calculation and is by no means intended to be taken as accurate - just a number that I arrived at. If that were true, the engine would tend to suffer the worst harmonics at 1,700 RPM, 3,400 RPM, 5,100 RPM, 6,800 RPM, etc. An improper harmonic balancer may allow these harmonics to increase in amplitude until the crank breaks from stress and overloading.

The guys at Chevrolet Engine in 1953 and 1954 were ANIMALS! "Them boys was some real studs", since they obviously had their she-ot together and did a lot of homework to design the bottom end, jacket layout, and cam placement of this engine. You'd be hard-pressed to find a group of engineers that could pull off such a feat today - and I include myself in that analysis (so don't take it personally). The design is a testament to the theory that extra iron, and lots of it, is a good foundation for solid engineering design. Overbuild, and the design can live almost forever.

THAT, boys and girls, is why I am unimpressed with the Far Eastern "technology" used in building engines (and probably many other things as well). Show me a Japanese engine design that still works well after fifty years, and I'll reconsider my position. Understand that the Vortec engine is still an iteration of the basic 1954 design, and you may grasp what I'm saying. The SBC lives on and is probably the envy of automotive engineers all over the world, regardless of whether or not they'll admit it. We're damn lucky that the engine design is so established, too, or we'd be paying a fortune for the engineering costs being absorbed in sales today - just like the Lexus and Acura customers have to pay a lot more for a lesser engine design. The Buick 231 is probably in the same category, which would explain why an engine first released in 1965 is still the desired engine among new car buyers 36 years later. In it's latest trim, it outperforms most offshore V-8s, gets better economy that most other V-6s regardless of displacement, and can be built to produce more power than a Nissan engineer's wettest dream.

Ford came very close with their Windsor engine design, but (unfortunately for them) they all but abandoned that case in the mid-90's for the Romeo engine project.

Any other questions?

P.S. - I'll try to stay off my stump now...

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Later,
Vader
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"Get UP - Drop the bombshell!"
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[This message has been edited by Vader (edited August 25, 2001).]

JETHROIROC

Vader, I'll have to second the 1,700RPM theory. My engine is it's roughest in the area of 1700-1900RPM, so I guess it's just the nature of the beast. Perhaps a Fluidampr would help smooth things out in this frequency range?

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1990 IROC 350
Mods: Too busy trying to make it run right to mod it.
Airfoil, Dynomax cat-back, MSD coil, 180 t-stat, Bald Eagle tires,
Hypertech fan switch, Accel 23# injectors, Holley AFPR, ported plenum,
Ported Daytona Yellow stock base, Moroso valve covers, other stuff,
Ruger P95DC, hot wife, new oil filter, thick rubber floormats, no cats.
18.0 @ 85MPH since I'm one big-a$$ MF
"It's better to have and not need than to need and not have."

Vader

Jethro,

The Fluid Damper theory seems sound, but I've never had experience with one in an automotive application. Large hydroviscous drive dampers seem to do a very nice job on large, low frequency machinery, though.

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Later,
Vader
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"Get UP - Drop the bombshell!"
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SSC

Jethoro, Ive heard only good things about fluid dampers. Stay away from TCI rattlers!
I just changed my crank at 10k because the rattler fryed.
SSC

Guest

The fluidamper is definitely an improvement over stock from my experience with one.

As for what a failed balancer can do, I did notice the difference in the smoothness of the engine, but I was not sure what it was. It seemed to be really bad at about 1400rpm and was present up to around 2000rpm. I couldnt feel it all that much at the higher rpms, it was there but not so noticeable. After checking the car, I noticed a nice shiny band across the front of the balancer and I knew it had slipped. Im not sure how many people would actually notice the difference if the balancer had slipped like mine, but I noticed it.

JETHROIROC

Mine sounds like it resonates in those ranges as well, madmax. I may be slapping in a Fluidampr in the next couple weeks...if I can sneak it by the wife! I'm just too damn **** to tolerate any imperfection.

gmanuel

Thanks for the replys. Please if there is anything more please add to the list. It seems that all the people that have asked the question there was never any postive feedback that the balancer was causing the vibreration at and around 2K rpm. If ever one gives their feedback then there will be a complete list for others to check and not have to ask the question agian. Since I am experiencing this problem I did not to spend the $ to buy and find it was not the problem. I could see no visible damage to the rubber and I did not know about the keyway and the timing mark should almost line up when I reassemble my engine. It appears that I will need to buy a balancer. Once I have installed I will give back my results.

GM

Guest

Actually yea, I just remembered something...

I had apparently set the timing after it had slipped but the balancer looked ok, because it didnt run as well as it should have and when I put the new balancer on the timing was like 20 degrees off. It just took a while for it to show me for sure there was something wrong when it slid back and left me a nice shiny spot to look at.

89bonestockiroc

I can tell you what my symptoms were when my harmonic balancer slipped. It was in a 79 z28 with a really nice 350 engine. I was driving down the freeway at about 3k rpm and then the balancer slipped and it decided to separate itself into about 1000 pieces. I dont know if that is a normal thing or not, but it sure did my engine in. I would not hesitate to replace it if you think its bad.
Mike

gmanuel

So to day I repalced the balancer. It had slipped. Now I know why I always had trouble starting the car when it was hot. The timing was to far advanced. I originally replaced the balancer because of vibration around 2k. Now it seems that there is a vibration at all speeds but they are deinitly not as hard as what I did have before. I guess I will need to keep looking for the vibration

Beast5spdGTA

I know this is old, but it's my exact question. I've been trying to hunt down a vibration(high freq)(like a vibrating chair)at about 75+mph. It increases on decelleration, but is very annoying on cruise control and WOT at anything above 80 mph. I know it's not the wheels b/c they're from my GTA(runs smooth to 130+). I tried an AL driveshaft(no effect). Also when shifting above 3000rpm it feels funny like the clutch grabbing a little, but it shifts great(no grinds power shifting).

I noticed in neutral the car shakes at idle ~600 rpm and ~1700 rpm (like you can see the seats move). Shakes a lot more than car in sig at idle.

Externally the damper looks alright, a small piece is starting to come out(at a seem?). I don't want to spend the money/time for a new balancer since I'll only be driving for 2 more weeks, but I have a 1200 mile trip to make and no vibrations would be worth $60.

This problem came after 2 yrs sitting and after a new clutch.
Can the flywheel be bolted up in different positions? causing an out of balanced engine? Also put in a poly tran mount.

gruveb

What do you mean slipped? How does it slip?

TBI305Camaro

A buddy of mine has a 85 custom deluxe with a 350 and when we went to pull his balancer off there was only 1 bolt!!!!! other two were completely striped...we had to screw huge bolts in to be able to pull it. His center crank bolt was a long *** bolt with 336378 washers on it...that motor was put together by 4 year olds i swear it was.

SpeedCat86

gruveb: "What do you mean slipped? How does it slip?

The stock harmonic balancer consists of of two steel pieces, an inner hub and outer ring, joined only by a thin layer of rubber elastomer. Older dampers, or ones subject to hight degrees of acelleration are prone to having the outer ring 'slip' in relation to the inner hub.
On my car, the outer ring slipped towards the engine, and started rubbing on the timing chain cover. It took me a while to realise this, and by the time I pulled the old one, the tc cover was nearly worn through.

gruveb

Thanks.

Guest

Just FYI, I've never seen one on a car move towards the front. Has something to do with the direction of rotation, torque, that kinda thing. Right hand rule. Living proof.

99Hawk120

Rotationally, a balancer should slip in exactly the opposite direction as it normally turns (because the outer ring can't "keep up" with the inner). As far as front to rear slippage, I would imagine that's simply because the car is driven forward most of the time. If you drag raced in reverse it might slip forward.

Damon

Yeah, I'll second the observation that the outter ring always slips backwards. In more ways than one, actually.

My grandmother's 78 Malibu had the balancer go south on it. The outter ring was slipping. Nobody really noticed it until one day there was an awful "shush, shush, shush" sound coming from the motor while running. Turned out the outer ring of the balancer slipped REARWARD and was starting to contact the timing chain cover!! Yikes!

I've had 'em go "boom" before and also had them fall off the front of the crank (taking the front crank pulley and all the belts with it) if the center bolt wasn't installed or the crank was old enough that it didn't have one.

Matt87GTA

Just another story about this....

The balancer on my 85 TA slipped and had me chasing my tail for a bit. I never caught it when trying to figure out why it was running like poop but the thing started making scraping noises from front of the engine after a few weeks. So I went under the car to take a look at what the noise was and the back of the outer ring was indeed in contact with the timing cover and resembled a brake rotor in its newly "machined" surface.