Harmonic Balancer Identification

[firebane]

So the continuing saga of my truck and its oddities about the thing. Today I saw down and started taking a look at the harmonic balancer that came off my truck in hopes of trying to track down what it came off of.

The first thing I did was measure across the balancer which came out to 6.75" and then I measured the thickness which came out to 1.25".

I visited Rock Auto and called a couple of parts stores and it seems that a 8" harmonic balancer is what should have came stock on my truck. The thing that now really has me scratching my head is on the back of the balancer I found the numbers 8653 stamped on it.

When I googled "harmonic balancer 8653" I got this result:
http://www.ebay.co.uk/itm/Marine-In...8653-6-3-4-1-1-4-M-4-Date-On-it-/150982860433

According to the number on this thing its a harmonic balancer for a marine v8? Is anyone familiar with this or perhaps give some insight into what the hell was on my truck LOL.

 

[bucket]

What location is your timing mark? A 6.75 balancer with a hollowed-out backside is typical of an 80's 305 for a car application.

 

[firebane]

What location is your timing mark? A 6.75 balancer with a hollowed-out backside is typical of an 80's 305 for a car application.

Timing tab is at 12 oclock. Engine is a pre 80s as the dipstick is on the left side.

I've read and checked many sites to try and find an answer on this but really can't get any definitive answer.

I'm going to be replacing the harmonic balancer regardless but I just wanted to ensure I am getting the proper one.

 

[bucket]

Timing mark at 12 and hollow on the back is almost certainly a carbed 305 balancer. If you have a factory timing cover with factory timing tab, I'd just get a balancer to match it.

 

[chengny]

Timing tab is at 12 o'clock. Engine is a pre 80s as the dipstick is on the left side.

That's the first "problem". A timing cover with the tab in the 12 o'clock position was only used from 1986 and up. So, if your engine is old enough to have a LH side dipstick, the currently installed timing cover is not original. See the image below:

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On an original timing cover for a pre-1986, the tab was located at about the 2 o'clock position. But, no worries - the tab position on the cover is not critical - because the proper damper can be installed to allow the use of a timing light.

Assuming you want to leave the current timing cover in place (and be able to use a timing light to set ignition timing), you will need a damper with a timing mark that is indexed 30 degrees CCW from the hub's keyway.

That way, when the crankshaft angle/piston stroke is at TDC, the damper's timing mark will be right in line with the 0 degree indent on the tab. This setup will allow you to accurately use a timing light with the engine running.

As far as the thickness and OD of the damper; those factors are not critical with an internally balanced engine. And we can safely assume that your motor is internally balanced just by the LH side location of the dipstick hole. For definite proof you would have to look at the crankshaft/rear main seal/flexplate configuration. A post 1986 engine is not internally balanced and as no counter weight on the end of the crank, has a one piece rear main seal and the flex plate does have that additional balance weight. I don't have any images of a pre-86 but here is a post 86 - which your engine should not look like.

A one piece seal (no external counter weight on the end of the crank):

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And an externally balanced flex plate:

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IOW: an internally balanced engine - like yours - does not require an 8" damper (it probably originally came with a 6 3/4" one), but it can use an 8".

On the other hand, an externally balanced engine (i.e. post 1986) really should have an 8" damper to counter act the additional weight on the flex plate.

 

[firebane]

Timing mark at 12 and hollow on the back is almost certainly a carbed 305 balancer. If you have a factory timing cover with factory timing tab, I'd just get a balancer to match it.

I'm curious what you mean by hollow on the back? Even what the Dorman replacement would be isn't a solid balancer and is hollow? Unless I'm not understanding your terminology for "hollow"

@chengny

Yeah I gathered it was the wrong balancer and timing cover on this motor.. Makes me wonder how it even ran or was timed properly.

I have included the offending image which I have marked the 12 position for the crank and the 0 mark on the balancer which according to your image would make it the proper balancer for the timing cover. But the balancer and timing cover are not what should be on the truck.

 

[chengny]

But the balancer and timing cover are not what should be on the truck.

I am not sure what that means. What "should be on the truck" (for most people anyway) is a damper/cover setup that allows the engine to be dynamically timed.

Other than that, since your engine is internally balanced, you could press virtually any damper onto the crank snout and it would run fine.

You would have to set the ignition timing by ear. But that is how I dial in the final ignition timing on a SBC anyway - correct timing mark/tab or not.

The factory spec timing numbers for these trucks were published years ago. Jeez, in your case, it was 1974. It was a whole different world back then. Just for example, gasoline had lead in it (and it didn't have ethanol). Your truck was a factory setup - just it came off the assembly line. The published original timing spec is basically useless after 40 years.

Just set an initial static timing of around 8 degrees BTDC and then dial it in by ear. It takes a few dives under the hood. But eventually, you'll find that sweet spot - the ignition timing where you get optimal performance and no pre-ignition ping or kickback on hot starts.

If, on the other hand, you may be looking to return your engine to factory condition. In that case, you will need to locate, purchase and install the appropriate timing cover. It will have the timing tab located at the position shown below (the image shows an aftermarket cover with an adjustable tab). Also, the timing mark on the OD of the damper will need to be indexed only 10 degrees off from the keyway (as indicated by the yellow arrow and black line). This image shows a mis-matched damper/cover. The damper is from a 1986 350 and the cover is for a pre-86. When installed, I timed it by ear and it ran great.

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Here is a pre 86 damper:

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[MadOgre]

Timing tab is at 12 o'clock. Engine is a pre 80s as the dipstick is on the left side.

That's the first "problem". A timing cover with the tab in the 12 o'clock position was only used from 1986 and up. So, if your engine is old enough to have a LH side dipstick, the currently installed timing cover is not original. See the image below:

You must be registered for see images attach

On an original timing cover for a pre-1986, the tab was located at about the 2 o'clock position. But, no worries - the tab position on the cover is not critical - because the proper damper can be installed to allow the use of a timing light.

Assuming you want to leave the current timing cover in place (and be able to use a timing light to set ignition timing), you will need a damper with a timing mark that is indexed 30 degrees CCW from the hub's keyway.

That way, when the crankshaft angle/piston stroke is at TDC, the damper's timing mark will be right in line with the 0 degree indent on the tab. This setup will allow you to accurately use a timing light with the engine running.

As far as the thickness and OD of the damper; those factors are not critical with an internally balanced engine. And we can safely assume that your motor is internally balanced just by the LH side location of the dipstick hole. For definite proof you would have to look at the crankshaft/rear main seal/flexplate configuration. A post 1986 engine is not internally balanced and as no counter weight on the end of the crank, has a one piece rear main seal and the flex plate does have that additional balance weight. I don't have any images of a pre-86 but here is a post 86 - which your engine should not look like.

A one piece seal (no external counter weight on the end of the crank):

You must be registered for see images attach

And an externally balanced flex plate:

You must be registered for see images attach

IOW: an internally balanced engine - like yours - does not require an 8" damper (it probably originally came with a 6 3/4" one), but it can use an 8".

On the other hand, an externally balanced engine (i.e. post 1986) really should have an 8" damper to counter act the additional weight on the flex plate.

A 1986 can be carbureted with a one piece seal. In fact they are well sought after for the benefit of the one piece seal as well as the ability to run pre 86 heads.

I had a 1986 305 4bbl drivers side dip stick with a one piece rear seal and a hollow damper as in the picture firebane posted. I do not remember where the timing tab was but if it has the one piece rear seal it will have the hollow damper and timing cover to match as it is internally balanced which is not the same as 85 and earlier.

If I remember correctly the timing was 4 degrees at 550 rpm stock

This is a 1986 only block. The 4.3s came with a one piece rear seal in late 85

 

[bucket]

I'm curious what you mean by hollow on the back? Even what the Dorman replacement would be isn't a solid balancer and is hollow? Unless I'm not understanding your terminology for "hollow"

The rear face of the ring is not flat like the front face. Basically, there is less material on the backside of the outer ring.

 

[firebane]

A 1986 can be carbureted with a one piece seal. In fact they are well sought after for the benefit of the one piece seal as well as the ability to run pre 86 heads.

I had a 1986 305 4bbl drivers side dip stick with a one piece rear seal and a hollow damper as in the picture firebane posted. I do not remember where the timing tab was but if it has the one piece rear seal it will have the hollow damper and timing cover to match as it is internally balanced which is not the same as 85 and earlier.

If I remember correctly the timing was 4 degrees at 550 rpm stock

This is a 1986 only block. The 4.3s came with a one piece rear seal in late 85

Interesting but I already know that this block is an older block by the 3970010 or whatever the number is.

 

[firebane]

The rear face of the ring is not flat like the front face. Basically, there is less material on the backside of the outer ring.

Looking at all the replacements I can buy are technically hollow.

 

[bucket]

Looking at all the replacements I can buy are technically hollow.

What replacement applications are you looking at? GM used a lot of variations over the years, and honestly, I wouldn't say one is better than the other. Just get one that lines up with the pointer on your timing cover.

 

[firebane]

What replacement applications are you looking at? GM used a lot of variations over the years, and honestly, I wouldn't say one is better than the other. Just get one that lines up with the pointer on your timing cover.

Anything by Dorman

I'll be stopping by the junkyard tomorrow to see if I can find a proper timing cover otherwise I'll just use a bolt on timing tab.

 

[bucket]

IMHO, there's nothing wrong with the style you have. Just make sure the new balancer matches it. Replacing the timing cover means dropping the oil pan.

And if you do get a new pointer, spend money on a good one from Jeg's or Summit. The cheap chrome ones are flimsy, inaccurate and hard to read.

 

[firebane]

IMHO, there's nothing wrong with the style you have. Just make sure the new balancer matches it. Replacing the timing cover means dropping the oil pan.

And if you do get a new pointer, spend money on a good one from Jeg's or Summit. The cheap chrome ones are flimsy, inaccurate and hard to read.

Pan is already dropped and getting a new gasket lol.