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Discussion Starter · #1 ·
I have 3 questions:

I've read through many posts about setting the timing on my 350 but none of them mention what RPM the engine should be at to check the timing. I've got the dwell/tach combo unit showing the engine at 800 RPM and the timing is set at what must be about 40 degrees btdc because the mark on the pully is about 3 inches before the 15 btdc mark on the plate with the vacuum line plugged! I'm also wondering if I'm looking at the correct mark on the pulley. On the crank pulley there is a sort of crease that runs the width of the pulley. There doesn't seem to be any other mark on it. I just can't believe with that much of an advanced timing it's not pinging like mad. Seems very odd.

1. Am I looking at the corrcet mark on the pulley?
2. What RPM should I be at to check the timing?
3. How many degrees btdc should I set the engine to? The prior owner put an Edelbrock model 1405 600cfm carb on it with a Weiand intake manifold. It has a "mild" cam in it but since I bought the car from his widow I can't get anything further. The car has no emission system and no cat either. Where I am in GA it's not an issue as we don't even have an emission test requirement. It's an 85 SS and he was the original owner and took great care of it. I want to continue that. I don't know what year the block is from as it's a 350 and the 85 SS from what I can tell only had a 305 from the factory. I tried both local parts stores for a Chilton or Haynes manual but enither had one for the El Camino.

Happy Halloween!

Thanks for any assistance,

Ron
 

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Take the distributor cap off and make a mark at the number one firing position. Turn the damper so the rotor is pointing at number one position. The TDC mark on the damper should be at the timing pointer or just before. I would start with about 8º BTDC for timing. Or advance the timing until you experience pinging under load and then back off the timing until there is no longer pinging.

Doug
 

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Timing 101, & then some.

Did you Read this ↓

Part 1 > http://elcaminocentral.com/showthread.php?t=27545

Part 2 > http://elcaminocentral.com/showthread.php?t=27544

Part 3 > http://elcaminocentral.com/showthread.php?t=27543

They are found in the "Articles in Category : Performance"

THEY will give you a better insight on Timing your Motor for Performance, or,
as MORE AND MORE are opting in doing, for Economy.

Also as Doug pointed out,(he's a pretty smart cookie he is, that Guy) Getting familiar with your Timing Mark is a MUST. :beer:
 

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Timing and vacuum advance 101

And to Provide you with a Better Understanding as to HOW YOUR VACUUM Advance plays a Part in all this, A little more Reading for you.
:dontknow:

TIMING AND VACUUM ADVANCE 101

The most important concept to understand is that lean mixtures, such as at idle and steady highway cruise, take longer to burn than rich mixtures; idle in particular, as idle mixture is affected by exhaust gas dilution. This requires that lean mixtures have "the fire lit" earlier in the compression cycle (spark timing advanced), allowing more burn time so that peak cylinder pressure is reached just after TDC for peak efficiency and reduced exhaust gas temperature (wasted combustion energy). Rich mixtures, on the other hand, burn faster than lean mixtures, so they need to have "the fire lit" later in the compression cycle (spark timing retarded slightly) so maximum cylinder pressure is still achieved at the same point after TDC as with the lean mixture, for maximum efficiency.

The centrifugal advance system in a distributor advances spark timing purely as a function of engine rpm (irrespective of engine load or operating conditions), with the amount of advance and the rate at which it comes in determined by the weights and springs on top of the autocam mechanism. The amount of advance added by the distributor, combined with initial static timing, is "total timing" (i.e., the 34-36 degrees at high rpm that most SBC's like). Vacuum advance has absolutely nothing to do with total timing or performance, as when the throttle is opened, manifold vacuum drops essentially to zero, and the vacuum advance drops out entirely; it has no part in the "total timing" equation.

At idle, the engine needs additional spark advance in order to fire that lean, diluted mixture earlier in order to develop maximum cylinder pressure at the proper point, so the vacuum advance can (connected to manifold vacuum, not "ported" vacuum - more on that aberration later) is activated by the high manifold vacuum, and adds about 15 degrees of spark advance, on top of the initial static timing setting (i.e., if your static timing is at 10 degrees, at idle it's actually around 25 degrees with the vacuum advance connected). The same thing occurs at steady-state highway cruise; the mixture is lean, takes longer to burn, the load on the engine is low, the manifold vacuum is high, so the vacuum advance is again deployed, and if you had a timing light set up so you could see the balancer as you were going down the highway, you'd see about 50 degrees advance (10 degrees initial, 20-25 degrees from the centrifugal advance, and 15 degrees from the vacuum advance) at steady-state cruise (it only takes about 40 horsepower to cruise at 50mph).

When you accelerate, the mixture is instantly enriched (by the accelerator pump, power valve, etc.), burns faster, doesn't need the additional spark advance, and when the throttle plates open, manifold vacuum drops, and the vacuum advance can returns to zero, retarding the spark timing back to what is provided by the initial static timing plus the centrifugal advance provided by the distributor at that engine rpm; the vacuum advance doesn't come back into play until you back off the gas and manifold vacuum increases again as you return to steady-state cruise, when the mixture again becomes lean.

The key difference is that centrifugal advance (in the distributor autocam via weights and springs) is purely rpm-sensitive; nothing changes it except changes in rpm. Vacuum advance, on the other hand, responds to engine load and rapidly-changing operating conditions, providing the correct degree of spark advance at any point in time based on engine load, to deal with both lean and rich mixture conditions. By today's terms, this was a relatively crude mechanical system, but it did a good job of optimizing engine efficiency, throttle response, fuel economy, and idle cooling, with absolutely ZERO effect on wide-open throttle performance, as vacuum advance is inoperative under wide-open throttle conditions. In modern cars with computerized engine controllers, all those sensors and the controller change both mixture and spark timing 50 to 100 times per second, and we don't even HAVE a distributor any more - it's all electronic.

Now, to the widely-misunderstood manifold-vs.-ported vacuum aberration. After 30-40 years of controlling vacuum advance with full manifold vacuum, along came emissions requirements, years before catalytic converter technology had been developed, and all manner of crude band-aid systems were developed to try and reduce hydrocarbons and oxides of nitrogen in the exhaust stream. One of these band-aids was "ported spark", which moved the vacuum pickup orifice in the carburetor venturi from below the throttle plate (where it was exposed to full manifold vacuum at idle) to above the throttle plate, where it saw no manifold vacuum at all at idle. This meant the vacuum advance was inoperative at idle (retarding spark timing from its optimum value), and these applications also had VERY low initial static timing (usually 4 degrees or less, and some actually were set at 2 degrees AFTER TDC). This was done in order to increase exhaust gas temperature (due to "lighting the fire late") to improve the effectiveness of the "afterburning" of hydrocarbons by the air injected into the exhaust manifolds by the A.I.R. system; as a result, these engines ran like crap, and an enormous amount of wasted heat energy was transferred through the exhaust port walls into the coolant, causing them to run hot at idle - cylinder pressure fell off, engine temperatures went up, combustion efficiency went down the drain, and fuel economy went down with it.

If you look at the centrifugal advance calibrations for these "ported spark, late-timed" engines, you'll see that instead of having 20 degrees of advance, they had up to 34 degrees of advance in the distributor, in order to get back to the 34-36 degrees "total timing" at high rpm wide-open throttle to get some of the performance back. The vacuum advance still worked at steady-state highway cruise (lean mixture = low emissions), but it was inoperative at idle, which caused all manner of problems - "ported vacuum" was strictly an early, pre-converter crude emissions strategy, and nothing more.

What about the Harry high-school non-vacuum advance polished billet "whizbang" distributors you see in the Summit and Jeg's catalogs? They're JUNK on a street-driven car, but some people keep buying them because they're "race car" parts, so they must be "good for my car" - they're NOT. "Race cars" run at wide-open throttle, rich mixture, full load, and high rpm all the time, so they don't need a system (vacuum advance) to deal with the full range of driving conditions encountered in street operation. Anyone driving a street-driven car without manifold-connected vacuum advance is sacrificing idle cooling, throttle response, engine efficiency, and fuel economy, probably because they don't understand what vacuum advance is, how it works, and what it's for - there are lots of long-time experienced "mechanics" who don't understand the principles and operation of vacuum advance either, so they're not alone.

Vacuum advance calibrations are different between stock engines and modified engines, especially if you have a lot of cam and have relatively low manifold vacuum at idle. Most stock vacuum advance cans aren’t fully-deployed until they see about 15” Hg. Manifold vacuum, so those cans don’t work very well on a modified engine; with less than 15” Hg. at a rough idle, the stock can will “dither” in and out in response to the rapidly-changing manifold vacuum, constantly varying the amount of vacuum advance, which creates an unstable idle. Modified engines with more cam that generate less than 15” Hg. of vacuum at idle need a vacuum advance can that’s fully-deployed at least 1”, preferably 2” of vacuum less than idle vacuum level so idle advance is solid and stable; the Echlin #VC-1810 advance can (about $10 at NAPA) provides the same amount of advance as the stock can (15 degrees), but is fully-deployed at only 8” of vacuum, so there is no variation in idle timing even with a stout cam.

For peak engine performance, driveability, idle cooling and efficiency in a street-driven car, you need vacuum advance, connected to full manifold vacuum. Absolutely. Positively. Don't ask Summit or Jeg's about it – they don’t understand it, they're on commission, and they want to sell "race car" parts.
 

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Discussion Starter · #5 ·
I can't wait to get some sleep now and get to work on her in the AM. First thing is to check the rotor to see when it's at the #1 piston, just where the pulley mark I'm using is. I wish I'd have done this before I changed the plugs because it would be SO much easier to turn the engine by hand with no compression rather than tapping the starter.

OK..I've read the info...so to make sure I understand...if I plug the vacuum advance then to set the timing correctly it really doesn't matter if I have the car idleing at 800 or 900. There's no "special" idle RPM to start with.

I just can't believe that my timing is currently so advanced and there's no pinging. As I said in my original post, my engine's final mark is 15 btdc and the timing light shows the mark on the pulley to be about 3 INCHES more advanced than that, ie, the mark on the pulley is farther to the left by 3 inches from the 15 deg mark on the plate.

Thanks all for you help. I'll post an update after I get through...or yell for help if I seem to be having problems along the way.

Ron
 

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Aside from all the great advice given above,, I'd start by verifying your timing mark and TDC #1 are correct. The sbc had two configurations. All early small blocks had the timing mark at roughly 30° clockwise from straight up (or roughly 2:30 o'clock position looking at the front of the motor) Later small blocks from the late 80's and 90's moved the timing mark to nearly straight up (actually about 8-10° CCW from straight up or about 11:eek:'clock). The timing 'tube' marked "0" degrees and was a small tube attached to the timing cover behind the waterpump. (mostly for computer controlled motors and wanted no advance at all, all advance was computer controlled)

SO see anything here adding up to roughly 40°... If your using a harmonic damper for a late motor, with a timing tab for a early motor,, it will show roughly 40° advanced when your really at TDC.

There is also the fact that after 40some years many of the elastomer type dampers have slipped. The outer ring no longer matches the key-way and the timing mark is fuber. Take a look at the rubber insulator between the ring and the center hub of your damper. If it's cracked and chunks missing. I'd bet a dollar to a donut the outer ring has slipped.


Best way to verify your timing mark is to remove #1 spark plug, remove the #1 rocker arms, insert a threaded piston stop into #1 plug hole and GENTLY rotate the motor BY HAND both clockwise and counterclockwise until you lightly contact the piston stop. The stop should contact equal distances both sides of TDC mark. THAT is where true TDC is.
BTW, I say remove the rocker arms from #1 because with a higher lift cam, and some heads the valves will contact your piston stop as the motor is rolled over. Removing the rockers will eliminate all valve action for that cylinder and save your sanity. If you have never had the fun of trying to get a bent piston stop out of a sparkplug hole,,, havent experienced FRUSTRATION yet. So proceed cautiously.
 

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And this is where the Rotor should be pointing, if your Distributor is in correctly ↓


..............crab type dist. cap→..............




If everything is correct as explained & shown above, and your still not getting your Timing mark to line up correctly, you either have the wrong Balancer, or your Balancer has slipped on it's rubber sleeve - if equipped.

Other than that, it would only leave that your timing Chain has slipped a tooth or two, (worn / bad chain) and will need to be replaced before causing any major damage to your Motor.
 

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Discussion Starter · #8 ·
Maybe the disk did slip. I'm placing two photos in this reply so I hope it's clearer for someone to possibly help me. I have turned the engine over until the rotor is at the cap contact for pistion #1. Then I looked again at the pulley to find the timing mark. I have cleaned the heck out of it and can't find any mark. What I did find was that the prior thing I THOUGHT was the mark is not. So the car is not 40 deg or so btdc. One photo is of the timing marks on the chrome cover. the 3rd point from the bottom is marked "0". The second photo shows the mark going across the width of the pully that I thought was the timing mark but there are several of these on the pulley. So, my problem seems to be that i can't find the mark on the pulley. I've done Google searches for photos of the pulley to see the marks but the ones I find have two mark like mine running across the width (one is marked "0" and there are numbers in between the two marks.
 

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Discussion Starter · #10 ·
I may have figured out the mark...maybe. I was plugging the wrong vacuum line and boy do I feel stupid! Anyway, now that I've plugged the correct vacuum line, once the engine is warmed, the mark i thought was the correct mark on the pulley is at 15-16 btdc according to the timing marks on the chrome plate. I'm just still not 100% certain that is the mark on the pulley. if someone looks at the photo of the pulley, it's the slightly rusted line running the thickness of the pulley. teh one in the photo is the one to the "right" on the pulley looking at it from the front of the car. There are two marks and the second one is the one that is to the left of the one in the photo and is at 15-16 deg btdc when warmed.

Anyone know if this is the correct mark on the pulley? it matches one's I've seen on the internet except I don't have any numbers between them, just the two marks.

Thanks,

Ron
 

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lol coyote you artist you. at least you did a pretty and straight line rather then just scribbling all over it like some people from vegas :)

I didn't have to worry about it being straight, it's the Machined Grove in the Balancer, (can't see no way any way) I just "Highlighted it with White-Out, ya know, that Correction Fluid stuff that us poor spellers use all the time.
But it DO make the mark really stand out when using
the timing light.:poke:
 

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Discussion Starter · #15 ·
Just an update and big thank you to you guys for helping me out! My pulley actually has THREE of those marks on it. SO much for my thought that one of the TWO was the timing mark. The car was not pinging so I used one of the marks to advance the timing about 4 degrees. It runs well and starts fine and doesn't ping. It could be too retarded but since I can't find a mark to use on the pulley, getting the #1 cylinder to tdc doesn't help me because I don't know what to use as a timing mark.

Anyway, I adjusted the edelbrock carb per the instructions and all seems great. I wish I could set the timing properly but I can't figure out how to find the timing mark on the pulley.

Thank for all your help as I learned a lot. I'm sure there will be more questions later. I have to find a lug nut cover for one of the factory 14" wheels and get the front end aligned. Then it's on to getting the interior door skins off and checking on why the key lock rod isn't connected to the locking mechanism. Keys turn fine in the lock but neither door lock engages. I want to make sure I have the door skin locking tabs in hand before I try to get the door off and have some break off.

Ron B.
 

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OK start here. Pull #1 spark plug and GENTLY roll the motor over with a breaker bar and 5/8" socket on the front damper bolt. (DO NOT USE THE STARTER) . Use a small flat screw driver and feel in the spark plug hole every few degrees for the piston to come to the top. Move GENTLY and EASILY so you feel when the #1 piston is as close to TDC as you can get. There is a long dwell as the crank swings over the arc of TDC but you'll feel the piston stop and start to move down again. When it does,,,,, Whichever mark on your balancer is close to TDC, That's the one you want to 'white-out' and use for setting your timing.

Option #2,, remove #1 plug, stuff about 2feet of an old spark plug cable in the cylinder (make sure and leave PLENTY hanging out so you can retrieve it. With the breaker bar and 5/8" socket gently roll the motor over CLOCKWISE till it wedges against the soft silicone plug cable. This will put the #1 cylinder somewhere around 10-20 degrees before TDC. That should give you a good hint of which mark on the damper is the correct one.

If you don't get the timing 'CORRECT' you'll never get the motor running at it's best. There is a lot of real experienced guys around this site, and I'll guarantee you NONE of them use a guess to set their timing,,,, they use a timing light and KNOW where their timing is set. Inaudible detonation is just as disastrous to your motor as loud pinging and obvious detonation. Your first 'hint' that something is wrong is holes melted in the soft cast pistons, or broken compression rings, destroyed valve guides... Do it right the first time and you'll be much happier with the results.
 
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