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I'm trying to figure out what the markings mean on the harmonic balancer on my '72 455 Supreme, and I'm hoping someone can help me out so I know what I'm looking at when checking my timing.
As far as I know, it was installed in the mid 90s when a PO did the engine work, so it's probably been superceded by a newer version. This would also explain why I haven't been able to find any info on the inner web.
I've included some pics of various markings, and I know there's a graduated scale from (IIRC) 0-36. I will post a pic of that when I get a chance, but for now, here's what I have.
This pic shows (what I believe) to be 90 deg...
...and this pic (taken on the opposite side) shows two lines...one shows (I think) BDC which would (I'm guessing) "before dead center," Th other line is just down from that and has a "nub" right in the center.
...any ideas?
Most engines like 34-36 degrees btdc to make the best power. Connect a timing light, rev and hold the engine to 3500 rpm, and line up the zero mark on the timing tab on the 36 degree mark on the balancer. Bingo, you have 36 degrees of timing.
The other marks are for lashing valves. An easy way to do it is to think about the firing order of the engine, split it in half like this. .
1843
6572
Cylinders 1and 6, 8 and 5, 4 and 7, 3 and 2 are companion cylinders, meaning they are both at TDC at the same time, just on different cycles of the combustion process. If you set the engine with #1 TDC on the compression stroke, you can set the valve lash on cylinders 1 and 6. Rotate the engine in the normal direction until the next timing mark lines up with zero on the timing tab, lash the valves on 8 and 5. Rotate another 90*, so cylinders 4 and 7, rotate another 90* and do 3 and 2. You have now set the valves and only rotated the engine once.
The above is not accurate. You can only set lash / preload on the cylinder that is on the compression stroke. The opposite will be on the exhaust stroke. When on the exhaust stroke at TDC you will be at overlap. Both valves can be open at that time.
Most engines like 34-36 degrees btdc to make the best power. Connect a timing light, rev and hold the engine to 3500 rpm, and line up the zero mark on the timing tab on the 36 degree mark on the balancer. Bingo, you have 36 degrees of timing.
And after doing the above, decrease the engine speed to 1100 RPM and make note of the number on the balancer that is adjacent to the “0” mark on the timing tab. That will be the initial timing setting for 36* total timing.
And after doing the above, decrease the engine speed to 1100 RPM and make note of the number on the balancer that is adjacent to the “0” mark on the timing tab. That will be the initial timing setting for 36* total timing.
Sounds good...do I need the hose unplugged from the dizzy when I drop it to 1100, and engine needs to be up to temp, correct?
Most engines like 34-36 degrees btdc to make the best power. Connect a timing light, rev and hold the engine to 3500 rpm, and line up the zero mark on the timing tab on the 36 degree mark on the balancer. Bingo, you have 36 degrees of timing.
The other marks are for lashing valves. An easy way to do it is to think about the firing order of the engine, split it in half like this. .
1843
6572
Cylinders 1and 6, 8 and 5, 4 and 7, 3 and 2 are companion cylinders, meaning they are both at TDC at the same time, just on different cycles of the combustion process. If you set the engine with #1 TDC on the compression stroke, you can set the valve lash on cylinders 1 and 6. Rotate the engine in the normal direction until the next timing mark lines up with zero on the timing tab, lash the valves on 8 and 5. Rotate another 90*, so cylinders 4 and 7, rotate another 90* and do 3 and 2. You have now set the valves and only rotated the engine once.
3500 seems like a lot...why so high? Also, I should remind you that the engine is .030 over with a W30 cam (specs unknown), Edelbrock Performer intake, Holley 770 Street Avenger and headers. Would the timing specs be the same as what you listed above?
The above is not accurate. You can only set lash / preload on the cylinder that is on the compression stroke. The opposite will be on the exhaust stroke. When on the exhaust stroke at TDC you will be at overlap. Both valves can be open at that time.
well, crap. I found a couple racing and engine building articles that describe basically the same method I described, but for whatever reason I can’t copy and paste the links.
Google valve lash adjustment shortcuts, one of the articles I found was on racing jalopy, another was a article by Pat Musi.
Sounds good...do I need the hose unplugged from the dizzy when I drop it to 1100, and engine needs to be up to temp, correct?
Definitely disconnect the vacuum advance. For this procedure your only interested in initial and centrifugal advance.
You want to rev the engine high enough to ensure the advance weights have fully extended. Chances are all the advance will be in at a lower speed, but 3500 should be plenty high enough.
Last edited by matt69olds; Aug 29, 2021 at 09:09 PM.
Definitely disconnect the vacuum advance. For this procedure your only interested in initial and centrifugal advance.
You want to rev the engine high enough to ensure the advance weights have fully extended. Chances are all the advance will be in at a lower speed, but 3500 should be plenty high enough.
I forgot to mention that I have HEI...does that make a difference?
Ok..here's my findings..
Idling at about 800 with vacuum advance connected: 34-36
Disconnect vacuum advance at 800 rpm: 10-12
Vacuum advance connected and increase rpm to 2800: Around 40-42...
At this point you have verified your initial advance is at 12 degrees and the vacuum canister gives 24 degrees.
You have no idea how much mechanical advance the distributor has, and you don’t know what the total mechanical advance is set to.
If you have a GM HEI, then the initial advance is likely way too low and therefore the total is low as well. This will limit performance, economy, and driveability.
At this point you have verified your initial advance is at 12 degrees and the vacuum canister gives 24 degrees.
You have no idea how much mechanical advance the distributor has, and you don’t know what the total mechanical advance is set to.
If you have a GM HEI, then the initial advance is likely way too low and therefore the total is low as well. This will limit performance, economy, and driveability.
ok but that link leads to 3 possible options race no vac advance, race vac advance, and street strip. It would seem you have a vac advance so its down to two options
the description says sun distrubutor machine set timing curve, but no specs.
The essence of what these guys are asking is how much mechanical advance does your distributor have and when is it all in by?
for reference my HEI still showed mech advance up to about 4k rpm. I dont recall the amount off the top of my head but maybe 24*, ill have to check my records
Definitely disconnect the vacuum advance. For this procedure your only interested in initial and centrifugal advance.
Fun71-
You want to rev the engine high enough to ensure the advance weights have fully extended. Chances are all the advance will be in at a lower speed, but 3500 should be plenty high enough.
You didn’t do that as Matt posted. At this point you have verified your initial advance is at 12 degrees and the vacuum canister gives 24 degrees. You have no idea how much mechanical advance the distributor has, and you don’t know what the total mechanical advance is set to. If you have a GM HEI, then the initial advance is likely way too low and therefore the total is low as well. This will limit performance, economy, and driveability.
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What they said. You did some right stuff but not the arguably most important - total mechanical timing.
Gotta get the mech wights to the end of their travel (~3500-4000 rpm, could be considerably lower), vac advance disconnected, set it to 36*. Recheck your base timing and you know your numbers.
Want some fun? Get an assistance to hold engine speed while you watch timing, yell to assistant the timing # so they can write down the rpm and advance, then have have them hold engine at next step, again recording rpm and advance, starting at idle, at 200 rpm intervals until timing no longer advances, which could be anywhere between 2000-4000 rpm which will give you numbers to plot your advance curve. Once you get those numbers, check back in for input.
You didn’t do that as Matt posted. At this point you have verified your initial advance is at 12 degrees and the vacuum canister gives 24 degrees. You have no idea how much mechanical advance the distributor has, and you don’t know what the total mechanical advance is set to. If you have a GM HEI, then the initial advance is likely way too low and therefore the total is low as well. This will limit performance, economy, and driveability.
————-
What they said. You did some right stuff but not the arguably most important - total mechanical timing.
Gotta get the mech wights to the end of their travel (~3500-4000 rpm, could be considerably lower), vac advance disconnected, set it to 36*. Recheck your base timing and you know your numbers.
Want some fun? Get an assistance to hold engine speed while you watch timing, yell to assistant the timing # so they can write down the rpm and advance, then have have them hold engine at next step, again recording rpm and advance, starting at idle, at 200 rpm intervals until timing no longer advances, which could be anywhere between 2000-4000 rpm which will give you numbers to plot your advance curve. Once you get those numbers, check back in for input.
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From what I can tell, I have the street/strip version and it has vacuum advance.
Im going to call the company tomorrow and ask for the specs on the unit. In the meantime from what I gather based on the replies, it makes no difference what type of HEI I have, I need to wind it out to 3500-4000 with the vacuum disconnected to get an accurate number on total advance, correct?
You didn’t do that as Matt posted. At this point you have verified your initial advance is at 12 degrees and the vacuum canister gives 24 degrees. You have no idea how much mechanical advance the distributor has, and you don’t know what the total mechanical advance is set to. If you have a GM HEI, then the initial advance is likely way too low and therefore the total is low as well. This will limit performance, economy, and driveability.
————-
What they said. You did some right stuff but not the arguably most important - total mechanical timing.
Gotta get the mech wights to the end of their travel (~3500-4000 rpm, could be considerably lower), vac advance disconnected, set it to 36*. Recheck your base timing and you know your numbers.
Want some fun? Get an assistance to hold engine speed while you watch timing, yell to assistant the timing # so they can write down the rpm and advance, then have have them hold engine at next step, again recording rpm and advance, starting at idle, at 200 rpm intervals until timing no longer advances, which could be anywhere between 2000-4000 rpm which will give you numbers to plot your advance curve. Once you get those numbers, check back in for input.
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What do you mean by "setting it to 36*? Am I moving the distributor to get to 36 or dialing up the timing light?
With car running, timing light set up, distributor turnable but not loose, have someone in the driver seat (herein known as “Driver”) as a throttle attendant and if you (herein known as ‘timer”) want to plot curve, attendant should have pen & paper.
Advance can be read by degree marks on balancer if there is a scale into the 36* range with a “fixed” light or “dial back” light (zeroed) OR off the “dial” after aligning TDC on balancer with “0” on timing tab. If using dial back light, you would align TDC on balancer with “0” on timing tab by turning the dial (or pushing buttons on digital) and read advance from the dial. To read total, adjust dial to align TDC on balancer with “0” on tab with engine steady at 3200-3400 rpm (assuming 3k stated by mfg), read dial to see the amount of advance.
Adjusting-
1. Disconnect vac advance & plug vac line.
2. At idle, check timing. Make mental note but it will likely change.
3. Driver brings rpm up to point where timer sees no more advance, which should be around 3000 rpm, timer yells, driver goes 200 rpm higher (for good measure) and holds engine speed steady.
4. Timer turns distributor to set timing at 36* and tightens distributor. You have now set total initial and mechanical advance. Engine can return to idle.
5. Idle can be reset if necessary, repeat #3 to confirm 36* with no further advance. Initial timing will be what it is, total will be 36*.
6. Can recheck vac advance total by putting hose on, it appears to be 24* iirc.
You would now have Base/Initial timing of xx*, Total Mechanical of 36* and Total w/ Vac Adv of 60*.
“Mech Total”(36) minus ”Initial”(12(xx)) equals “Mech Adv.”(24) (ex 36*-12*=24*)
IF you want to plot curve, disconnect vac advance & plug line.
1. At idle, timer yells advance # to driver who writes down rpm & timing
2. Driver raises engine speed 200 rpm & holds steady, writes down rpm, timer yells timing and driver writes that down next to rpm.
3. Driver again raises engine speed 200 rpm & holds steady, records rpm, timer shouts the timing and driver again records it.
4. Repeat every 200 rpm until no more advance occurs, which will be around 3000 rpm (according to mfg) but go 1-2 rpm steps past to be sure.
You now have an advance curve so you know the rate and plot of the curve, you can make a quick graph that provides a good visual.
At this point you know all your numbers pertinent to your ignition timing. Adjustments can be made if necessary. Post info up for people to scrutinize.
Although a wordy process it is actually a 5 minute process.
