Bad harmonic balancer symptoms?

[84 W40]

A quick way to check if your ring on the balancer has moved, take the spark plug out on the number one cylinder and disconnect the positive wire red to the distributor. Put your thumb on the sparkplug hole and have someone bump the starter until you start feeling compression to the point it wants to move your thumb. Piston is at TDC or very close to it, look at the line on the balancer it should be lining up with your 0 on the timing tab. If the line on the balancer pointing at lets say 20 degrees or more the ring on the balancer is moving.

 

[fleming442]

I thought rough idle was a standard feature

 

[Clone TIE Pilot]

I will go ahead and order a new balancer. Even if the outer ring hasn't slipped, the fact the rubber is rotting means the damper can no long absorb the harmonics which can cause a rough unsteady idle according to articles I have read online. I will also try replacing the PCV valve too.

When I smoked the engine I did notice a little smoke from the stem on the EGR valve. Not the diaphragm, at the base that bolts to the intake manifold, not sure if that is normal? Its a GM valve with low miles.

 

[bracketchev1221]

I will go ahead and order a new balancer. Even if the outer ring hasn't slipped, the fact the rubber is rotting means the damper can no long absorb the harmonics which can cause a rough unsteady idle according to articles I have read online. I will also try replacing the PCV valve too.

When I smoked the engine I did notice a little smoke from the stem on the EGR valve. Not the diaphragm, at the base that bolts to the intake manifold, not sure if that is normal? Its a GM valve with low miles.

If your harmonics are that bad you have other issues.

 

[lilbowtie]

Wasn't trying to be funny on the Google comment - lots of info there!

 

[Clone TIE Pilot]

The tt

If your harmonics are that bad you have other issues.

The GM factory manual for Monte Carlos states that if the outer damper ring slips, the entire damper loses its harmonic tuning and no longer controls the harmonics, regardless of internal or external balancing. Harmonic dampers are tuned for their engine application. Different engines, even different SBC models have unique harmonic frequencies which the damper must be tuned to match. Sometimes hotrodding an engine can shift the harmonics out of the stock damper's range to control.

Googling symptoms of bad harmonic dampers, some of the results I get are excessive vibrations similar to an unbalanced wheel, uneven RPMs, squealing, and rough idle. On Thirdgen, one guy had a damper that slipped and the harmonics snapped his crank and camshaft. Other guys there reported having rough uneven running cured by replacing bad harmonic dampers. Further searching shows that when a bad damper no longer absorbs harmonics, the harmonics can mimic knocking and make a otherwise healthy gas engine sound like an old 80's diesel about to shake itself apart. That is engines produce tons or harmonics that must be controlled by the damper for smooth operation and avoid fatigue failures. Moreover, harmonic damper issues are often overlooked. The rubber in dampers can dry rot over time and crack from just the passage of time, so its an item that should be replaced in old engines.

I ran a compression test and all cylinders are good and close to each other, smoked the engine and no vacuum leaks. The cap, rotor, coil, spark plugs, and upgraded heated O2 sensor are all new. The choke is working correctly.

 

[bracketchev1221]

What does the engine do at higher rpm?

 

[Clone TIE Pilot]

It smooths out at higher RPMs which I know often indicates a vacuum leak but the smoke test showed there are no leaks. In my online searching some sources say the vibrations should get worse with RPMs with a bad damper while other sources say that is not always the case, that bad dampers only affect certain RPMs such as idle. If the damper did slip, then the timing mark could be off which in turn could mean the ignition timing is off and affecting idle.

Just in case I have just replaced the PCV valve, the old one does not appear to be stuck but the pintle inside sounds looser than the new one. Both are A/C Delco PCV valves. A bad or incorrect PCV valve can mimic a vacuum leak and lean out the fuel mixture.

Only other vacuum leak source I can think of is the tiny smoke seepage I witness from the EGR stem going into the base. Can't find anything online about EGR stem sealing. Only can find about diaphragm and coking issues which my EGR valve doesn't have, its also a A/C Delco valve.

 

[565bbchevy]

If the damper did slip, then the timing mark could be off which in turn could mean the ignition timing is off and affecting idle.

I will agree that the damper can't do it's job correctly if the outer ring slips but even though the timing marks will have moved this aspect has no affect on your actual timing unless you tried to reset it to where the mark is now.

 

[fleming442]

How old is the fuel?