Topic: got my balancer off now............

[1onehotTA]

Hey guys, I got my balancer off, but now have another question.  Are everyones timing marks, like a precast into the timing chain cover?  I just want to be sure my car doesnt have any olds parts that the previous owner my have put on, as it is a Pontiac W72.  And obviously with the wrong marks my timing would be off.
           I got it off and on pretty easily also, my old one was off around 1/4 inch counterclockwise, but it may have been moving at times too, at least with just eyeing it up to the new one it was 1/4

[Tin Indians Rule]

Your timing marks should not be cast into the t/c cover. They should be on a plastic indicator that is mounted to the t/c cover via a dowel pin and bolt that will be behind the harmonic balancer.

[whwright]

If someone in the past has changed the timing cover, they might be cast into it.  My '78 model has the "removable" timing indicator, while my son's engine (which came out of a '76 Bonneville) has the "cast" timing indicator.

[1onehotTA]

So actually then if I have marks cast into the cover they would be the same as having the plastic indicator type.  In other words, what im getting at is there is no chance that like a TC cover from an Olds engine or not compatable GM engine's cover would fit my Pontiac 400 and the marks would then be off because this TC cover happens to fit a 400 W72 engine but the timing marks are not correct.  I am really curious because the marks go up to 16 degrees on it, but they are not numbered, I would think if 16 was its correct timing that it would say the number 16 on it, instead it has numerals upto I believe 12 then it goes to lines, and the last line is 16.  Maybe im just reading too much into it, also the the number 16 would make too much sense LOL.  But if I would of designed these marks, I would of put 16 in the middle then had like 18 and 14 before so you know like how far off you would be exactly from 16, Does that make sense LOL.

[ta78w72]

They could be off if the harmonic balancer on the olds was a difference size.  Aren't you measuring degrees from TDC.  There would be 360 degrees on the balancer.  If the balancers were different circumferences, then each degree would be a different distance and the timing marks would laid out differently.  You can check this mathmatically by measuring the circumference of the balancer.  Then measure the distance for a set amount of degrees.  Figure out what the distance per degree is and multiply by 360.....you should get the circumference of the balancer if the timing marks are correct.

[whwright]

Actually, regardless of the size of the balancer it will go around once per revolution.  And the distance from the indicator to the center of rotation wouldn't change so the marks would still be correct.  But, if you for some reason have an Olds balancer there will be an extra quarter-inch of space between the balancer and the indicator, making it hard to read with a timing light.  On my Pontiac motor there is only an eighth inch or so between the balancer and the indicator.

By checking eBay items, it appears that the Pontiac balancer is 6.9" diameter, while the Olds balancer is 6.5" diameter.  That equates to a circumference of 21.7" for the Pontiac and 20.4" for the Olds.  If you're still worried that yours might be wrong, measure it and see what you find out.  The easy way to do that is to put a string around it, mark the circumference, and measure the string with a tape measure.

It's also possible the outer ring of the balancer has slipped around the inner ring, putting the mark in the wrong position.  If you think that might have happened, you can find the correct position (or verify that your mark is already correct) -- but it takes a little bit of careful work.

Wayne.

[ta78w72]

whwright, that's right, the revolutions are the same regardless of size, and the number of degrees are the same.  But the distance between degrees has to be greater on a larger circumference balance.  So, if the balancers were different sizes, the timing marks must be laid out differently to accommodate this difference.

For example, if you had a balancer that was 360 inches in circumference, each degree would be one inch.  If you had a balancer that was 180 inches, each degree would be one half inch.  In the first case, timing at 16 degrees BTDC would be sixteen inches.  In the second case it would be eight.  I realize my example is exaggerated, but I did that to emphsize the point.

It seems logical to me.  Am I mssing something?

[whwright]

Well... maybe I'm not understanding you correctly.

On every car I've ever had, the "degrees" are shown on the indicator, with a single mark on the balancer.  Regardless of the size of the balancer, the indicator stays put.  The distance between marks on the indicator is a function of its distance from the crank centerline.

I thought of something else overnight.  If I recall correctly, a Pontiac engine is internally balanced, so the thing we all tend to call a "balancer" is actually a "harmonic dampener."  An Olds engine is externally balanced, so the "balancer" really does have an assymetric center of gravity (i.e. it really is a "balancer.")  If you put an Olds balancer on a Pontiac (or vice-versa) I'm not sure the engine will be properly "damped."

Wayne.

[ta78w72]

You're correct about the harmonic dampener cause I too believe the engine is internally balanced.

And, you're correct that the degrees are shown on the indicator.  And you're right that the indicator stays put.  Where we're not communicating is that the indicator is "mated' to the harmonic dampener and you can't change the size of the dampener and expect the indicator to be correct.  The scale would be different for each size of dampener.  

So we're back to the original question from 1onehotTA " if I have marks cast into the cover they would be the same as having the plastic indicator type. In other words, what im getting at is there is no chance that like a TC cover from an Olds engine or not compatable GM engine's cover would fit my Pontiac 400 and the marks would then be off because this TC cover happens to fit a 400 W72 engine but the timing marks are not correct. "

To answer his question, the indicators would be true no matter if on the timing chain cover or the plastic type (I thought they were metal) as long as the harmonic dampeners were the same size.  If they are different sizes, then the markings on the indicators would not be true and the timing, if set according to the indicator, would be off slightly.

So, Eagle1.....what are your thoughts on this?  This is a technical forum and we're all getting hung up in a math problem! :?

[Eagle 1]

First of all, every Pontiac 400 that I have worked on from 69-79, the timing marks were cast into the timing cover and not adjustable.  If they make a timing cover that has adjustble timing marks, I have never seen one.
To my knowledge you cant interchange a Pontiac timing cover and an Oldmobile timing cover.  Pontiac timing covers are unique in design as to the rest of GM products.   The water pump on a Pontiac engine is integrated into the timing cover.
As Wayne pointed out, a Pontiac engine uses a hamonic damper where as an Oldmobile uses a harmonic balancer.   They are not interchangeable.  If you cranked an engine up with the wrong one on, you would know it immediately due to the excessive vibration.  Im not even sure that will an Olds will fit a Pontiac due to the crank size, but Im not an Olds man, so Im not sure on that.
I suspect the old harmonic dampner timing mark has slipped and is not in the original spot.  This is very common, even mine is that way.  As the rubber inside the dampner heats up and cools down, plus old age,  will cause it to slip.   You just have to compensate while setting your timing, or replace the dampner

As far as the degree difference,  sorry Im not going to get into that arguement. :lol:

[Eagle 1]

Here is a picture of my timing cover.  Notice I circled the timing degree numbers which are a part of the timing cover.
You can see my timing mark on the harmonic dampner at about 1'00 clock.
I hope this helps to clear things up.

[whwright]

Wow Eagle 1.  That engine just doesn't do that shaker justice.

Your cover looks exactly like my son's engine that came out of a '76 Bonneville.

Here's what the cover on my '78 T/A looks like.



You can see that it's plastic, and secured by two of the front cover bolts.  I think the marks are in exactly the same position.  I have no idea what the round-fitting-looking-thing was intended for.  Maybe the Pontiac engineers were looking ahead to some sort of crank position sensor.

Wayne.

[1onehotTA]

Well I think that definitely clears up my balancer/timing mark issue, the balancer is new and correct.  I am trying to solve my knocking issue, I put 94 octane and it halted SOME, but not all together, I bought a weight/spring kit last night and messed with it today, I have it on the firmest springs and it still knocks.  I think im gonna try an adjustable mechanical vacuum advance next.   Its seems as though my knocking starts right around when I start to get on it, 2000 rpm and ceases somewhere when the engine starts to rev higher I do have a question though, would it hurt if I drove my TA for a short distance with the mechanical vacuum advance disconnected to see if it knocks then?  Or will that harm the pistons or something internally?

[ta78w72]

Very interesting.  The standard 400 has a different timing indicator than the W72.  Another interesting thing is the W72 is timed at 18 degress BDTC and the standard 400 is 16.  And the indicator on the W72 has the last number of "12" and then three or four little dashes....with each dash being 2 degrees.  So you time the car to almost the last dash.  While the indicator on the standard engine goes up to 24 degrees.  My daughters indicator also has a few degrees ATDC.

Also, my daughter's 77 (where I got the data for the standard 400) seems to be made out of metal and not part of the timing cover but attached to it.  I haven't looked that closely....but from the quick look I did.....it's not part of the timing chain cover.

1onehotTA....you better solve than knocking problem.  You don't need to disconnect the vacuum advance to see if it will knock.....it will knock if you do that.  Sounds like you've got a timing or vacuum issue....when you begin to stress the engine it knocks.  Are you running a stock distributor?  And is the vacuum advance unit sound?

[Eagle 1]

That cover appears to be made differently than the ones I have seen.
I would like to see a whole picture of it.
These are the only ones I have ever seen.
I am thinking it looks more like a 350 cover rather than a 400 cover.