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  #1  
Old Jun 12th, 05, 8:24 AM
drielly drielly is offline
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Default Harmonic Balancer - how can you tell if it's working?

How do you “test” or determine if your balancer is still working properly? I am attempting to determine the source of a vibration, and the balancer I would suspect could be the culprit…among a myriad of other rotating assembly choices on the engine. It’s a SB 350, warmed over, nothing radical…6.75 balancer. I am 99.999% positive it is an engine and not a drive train, wheel balance, body bushing, etc… vibration.



Totally RPM related….not MPH or gear related. It’s not an outrageous knock you off the seat vibration…but annoying as heck and I know it shouldn’t be there. It occurs repeatedly right at 2000 RPM …no matter my speed or what gear I am in…clutch in, clutch out, in gear, out of gear. As you accelerate past 2000 you can feel it…and as you decelerate and “pass through” 2000 RPM it is most pronounced…below 2000 it’s fine.



I have replaced the belts, and my alternator…belts were OK, alternator needed a refresh anyways. I definitely can see a bit of belt “wobble” on the accell and decell from the alternator down to the balancer. Nothing outrageous, but I can see it. I have tightened up the belt, but afraid to overcrank it and wear out the alt and water pump bearings. All of the pulleys seemed to be lined up OK



When the car is idling, the balance/crank looks out of “round” as it rotates, but then when you rev it, it “smooths” right out as I would suspect it is due to the operation of the balancer. How do I check if that is correct…without pulling the balancer? You read the other posts about the war stories pulling and putting on the balancer, I’d like to avoid it if I could.



I am definitely going to get rid of the clutch driven fan and go with a Derale flex fan for the performance issues over a stock clutch fan and it possibly could be the problem…though it “looks” ok as it spins up and down with the motor.
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  #2  
Old Jun 12th, 05, 11:16 AM
pukes66 pukes66 is offline
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Default Re: Harmonic Balancer - how can you tell if it's working?

For the money, I would replace the balancer with a new one. I have had two instances recently in which I reused the stock balancer the outer ring has slipped on the rubber. On one of the engines, the outer ring moved back and contacted the timing cover and made some awful noise. The second time, the ring slipped and moved the timing mark, which made it impossible to time the engine. A new stock type balancer will cost $50-$80 at any parts house. I have seen them in Northern Automotive for $80 for their hi-perf model. As for removal, it can be done in-car and should take an afternoon. Just my 2 cents.
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  #3  
Old Jun 12th, 05, 4:06 PM
drielly drielly is offline
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Default Re: Harmonic Balancer - how can you tell if it's working?

But again...ttt....why replace it if it's working OK? If there's a test of some sort, I'd like to try it before I replace it...or the myriad of other parts that might be the source. I read so many threads and TC'rs wind up replacing part after part with no results. I am attempting to take a methodical approach to this one without making NAPA auto rich.


anyone???
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  #4  
Old Jun 12th, 05, 7:54 PM
BillK BillK is offline
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Default Re: Harmonic Balancer - how can you tell if it's working?

d,
There is no test that I know of to see if a damper is working correctly. If the rubber is not all cracked up, and the timing mark is still in the proper location, its probably ok. Only way to tell is to replace it.
To be honest with you though, I would doubt that the damper was the problem if the "vibration" occurs at 2000 rpms. Are you sure it is not a "rough running" condition, as compared to a "vibration" ? Sometimes it hard to tell the 2 apart. Is this something that started happening recently, or has this engine always done it ?
One thing you might want to do is remove all the belts and start the engine and try it. You should be able to run it long enough without hurting anything. At least that way you will eliminate the clutch fan, alternator etc.
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  #5  
Old Jun 13th, 05, 8:00 AM
drielly drielly is offline
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Default Re: Harmonic Balancer - how can you tell if it's working?

Bill:

It's something that I noticed recently this year. Always had a vibration of sorts, nothing horrible, but I think this 2k vibration was masked by other suspension driveline issues. Over the winter I replaced the entire suspension front to rear, along with the driveshaft (Denny's'), u-joints, springs, control arms bushings, front tie rods, shocks, you name it....complete refresh...handles great.

Because of that I was convinced it was a driveline vibration, most notably a pinion angle. I had moved the angle up and down a million different positions and it didn't go away. But only last week by chance I did the old drive down the road, put it in and out of gear, clutch in and out a number of times at differenet speeds and finally realized it wasn't a driveline or speed related issue at all, but definitely from the rotating engine....it's always at 2000 rpm.

It's most noticeable as a "shutter/shake" type feeling as it passes through the 2k mark on a deceleration. It's repeatable every single time. It's a lot easier to notice when I am actually in gear and using the engine to slow me down. By just driving along, pushing in the clutch or taking it out of gear and revving the engine it's a bit tougher to feel because the driveline connects everything to magnify the vibration. Even sitting at a standstill and revving it, or coasting out of gear it is tough to notice for you pass through the 2k mark in a second. But if I take the time and hover up and down the 2k mark I can feel it, not as pronounced as when in gear driving, but definitely appears to be the "source".

I am going remove all the belts some time this week to see what happens. I did remove the alt belt and drive it down the street, but scared as all heck that I'd melt the engine with no water pump or fan...engine was already warm. I'll try it again, but with the engine cold to give me a bit more time to isolate it if at all possible.

Any other thoughts?

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  #6  
Old Jun 13th, 05, 9:24 AM
abob abob is offline
 
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Default Re: Harmonic Balancer - how can you tell if it's working?

.
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  #7  
Old Nov 4th, 06, 6:41 AM
hrd hrd is offline
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Default Re: Harmonic Balancer - how can you tell if it's working?

if it looks like it wobbles at idle...replace it, it maybe that you just cant see it happening at a higher rpm, at least take the belts and pulleys off and see if everything looks good, my guess is the elastomer fillling is departing the scene, be careful if you rev it like that though, it may come apart....and, if performance is what youre after, i read a test by a radiator company (i think it was) recently that said a properly operating stock clutch fan is one of the least hp robbing setups of any besides electric, and some of the differences were quite surprising, like 15 to 20 hp and more surprising
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  #8  
Old Nov 4th, 06, 1:08 PM
Tom Mobley Tom Mobley is offline
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Default Re: Harmonic Balancer - how can you tell if it's working?

what hrd said. going to a flex fan is a step backward, not forward, especially if you're concerned about vibration issues.

try the "no belts at all" thing. As Bill said, it's very unlikely that the balancer is the source of the vibration. Minor issues with the rim slightly out of alignment with the hub are not a big issue unless it's actually loose. If it is it will walk off the front or the back.
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Last edited by Tom Mobley; Nov 4th, 06 at 3:00 PM.
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Old Nov 4th, 06, 1:37 PM
LevonH LevonH is offline
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Default Re: Harmonic Balancer - how can you tell if it's working?

This may sound odd, but check the dist weights. A faulty or mis-functioning dist can set up a condition where the engine shakes as the timing flutters. Saw that on a higher compression big block and it shook JUST before it detonated on the way up the RPM scale.
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  #10  
Old Jun 18th, 14, 5:06 PM
Neon John Neon John is offline
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Default Re: Harmonic Balancer - how can you tell if it's working?

The 2K RPM vibration on my 86 El Camino may be the harmonic balancer? I replace it with anew one from Summit. The engine numbers shop the block is a 1975 350 4 bolt. Does that motor require a 1975 balancer? any body got a part number for that???
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  #11  
Old Jun 18th, 14, 8:14 PM
zombie1969 zombie1969 is offline
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Default Re: Harmonic Balancer - how can you tell if it's working?

Whenever I got a vibration that I was sure was from the engine I'd replace the cap rotor and wires. Fixed it every time. They don't seem to last very long with a high output ignition and header heat so close. Got to the point I had a new set in the trunk just in case.
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