Dampener (Torsional Vibration Dampener/Harmonic Balancer)

[DoubleDingo]

Last weekend I noticed the dampener isn't rotating true anymore. I want to replace it with a new one before it comes apart. I was going to place the order on Summit just now, thinking it would be an easy purchase. I then see there are various options. 8", 6.75", with degree marks, without degree marks. Was hoping to see AC Delco as an option, but no. Dorman, the mark is clearly not lined up with the keyway. The summit brand ones, they appear to have the zero lined up with the keyway, and have degree marks. I don't care one way or the other about degree marks, but to keep it simple, the one mark is sufficient.

I can measure the diameter so I get the same size. But what is deal with the mark? Are they supposed to be lined up with the keyway? Is the keyway TDC at zero on the tab? Any info is much appreciated. Thanks.

 

[legopnuematic]

GM changed the location of the timing pointer a couple of times over the years. My 76 has the “normal” 2 o clock position for the timing tab, whereas my 79 has it at 12 o clock, and must shoot the timing gun behind the water pump.

Any can be used as long as it has the appropriate timing cover or pointer bolted on

 

[DoubleDingo]

GM changed the location of the timing pointer a couple of times over the years. My 76 has the “normal” 2 o clock position for the timing tab, whereas my 79 has it at 12 o clock, and must shoot the timing gun behind the water pump.

Any can be used as long as it has the appropriate timing cover or pointer bolted on

As you explained that, I realized I have some photos of the timing cover, dampener, and timing gears & keyway. This should help with information I need.

That last pic with the clean engine, if I recall correctly, and it does appear to be so by looking at it, but it appears be to at zero/TDC.

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[DoubleDingo]

I can't find the specifics on the dorman 594-006, but that is the only one that comes up for my application.

 

[legopnuematic]

That should be correct for the 12:00 position pointer. I think I put a dorman on my 79’s 350. Think my 76 has an ATP Graywerks balance. Both seem ok.

 

[DoubleDingo]

Ordered it from my local parts store. Can pick it up later today

 

[Snoots]

Yank those POS steel water jacket plugs out and install BRASS plugs. You're welcome.

 

[DoubleDingo]

Yank those POS steel water jacket plugs out and install BRASS plugs. You're welcome.

Never crossed my mind, thanks for the heads-up.

 

[Snoots]

I've had mine rust thru and leak before. The one on the back of the drivers side head. If the motor had been out it would have been an easier fix. Lesson learned for me the hard way. Just trying to save you the headache.

 

[DoubleDingo]

I've had mine rust thru and leak before. The one on the back of the drivers side head. If the motor had been out it would have been an easier fix. Lesson learned for me the hard way. Just trying to save you the headache.

Yeah, it was out maybe 9 years ago. Those freeze plugs are probably factory. They have definitely lived their useful life.

 

[ChuckN]

@DoubleDingo I got to thinking about this and turns out the harmonic balancer /timing tab varies a lot over the years. I did a quick google search and this is one of the more helpful posts over on NastyZ28.


They used the 1:30 position and the 12:00 position interchangably from the late 70s through until the Vortec motors came along (1996). Both locations were used with either the smaller 6-3/4" and larger 8" balancers.

Your IROC with the TPI engine uses a 1:30 position timing mark, but if you had an 87-up IROC with the 305 TBI motor it would use the 12:00 position timing mark.

It's not just year or model, it's engine by engine.

The ONLY thing you can depend on is the location of the timing keyway on the crank/inner hub of the balancer. It is ALWAYS is in line with the #1 crank journal (it points exactly 45* to the right of straight up when the #1 piston is at TDC). You can remove the crank pulley and judge TDC by the position of the keyway.

A balancer designed for a 12:00 position timing tab will have a 45* offset from the timing line to the crank keyway. A 1:30 position balancer will have a 13* offset between them. Pretty obvious difference between the two. But you have to take the crank pulley off to see it.

 

[DoubleDingo]

@DoubleDingo I got to thinking about this and turns out the harmonic balancer /timing tab varies a lot over the years. I did a quick google search and this is one of the more helpful posts over on NastyZ28.


They used the 1:30 position and the 12:00 position interchangably from the late 70s through until the Vortec motors came along (1996). Both locations were used with either the smaller 6-3/4" and larger 8" balancers.

Your IROC with the TPI engine uses a 1:30 position timing mark, but if you had an 87-up IROC with the 305 TBI motor it would use the 12:00 position timing mark.

It's not just year or model, it's engine by engine.

The ONLY thing you can depend on is the location of the timing keyway on the crank/inner hub of the balancer. It is ALWAYS is in line with the #1 crank journal (it points exactly 45* to the right of straight up when the #1 piston is at TDC). You can remove the crank pulley and judge TDC by the position of the keyway.

A balancer designed for a 12:00 position timing tab will have a 45* offset from the timing line to the crank keyway. A 1:30 position balancer will have a 13* offset between them. Pretty obvious difference between the two. But you have to take the crank pulley off to see it.

Post #3 shows my engine. I am hoping the dampener I bought is correct, as it was the only one for my application. We shall see. Thank you for the detailed explanation, though, I can check that info against my other engine and this one when I swap in the new dampener, but I won't be taking off the gear, just a simple swap. The seal is good, it's not seen a lot of revolutions.

 

[ChuckN]

Post #3 shows my engine. I am hoping the dampener I bought is correct, as it was the only one for my application. We shall see. Thank you for the detailed explanation, though, I can check that info against my other engine and this one when I swap in the new dampener, but I won't be taking off the gear, just a simple swap. The seal is good, it's not seen a lot of revolutions.

Hey, happy to do some digging- I just copied and pasted what some other dude wrote (sorry, should’ve been more clear about that).

 

[DoubleDingo]

Hey, happy to do some digging- I just copied and pasted what some other dude wrote (sorry, should’ve been more clear about that).

Lol...it's all good. I checked the new one, and it appears to be correct judging by the pics of my engine and OEM balancer