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Old 10/08/10, 12:24 PM   #1
Bundy
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Setting the timing on my 302

As I try to set my timing for the first time on my carbuerated 94' 5.0, I am trying to know was much as I can before I go and pick up a gun and attempt to set the timing. I just installed the explorer serpentine conversion and had a complete top end rebuild- I have a mallory unilite comp 9000 breakless dizzy.

I found this MSD video of a small block chevy on youtube which brought up some questions as they apply to my engine.
http://www.youtube.com/watch?v=UYGU7mTwsZc

In the video they talk about 3 important parameters or a range that the timing should be set, and I have no idea the range.

The parameters mentioned in the video are all advanced before TDC:

1. Initial timing setting (for idle) for small block chevy is 12 degrees

2. Total timing (highest advance for higher RPM)

3. Ignition Timing Mechanical Advance (curve; rate of timing advance)


So my questions are:

1. To find the initial, I need to find TDC. When I had the valve covers off I had it marked slightly after 0 degrees TDC (retarded). Did I screw that up? What is a common TDC to start?

2. How do I figure out where the total timing or the highest degree of advance should be?

3. On my mechanical advance dizzy that was already in the motor, does it automatically set the curve itself?


Please bare with me on my ignorance, but this is how I learn.
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Old 10/08/10, 12:52 PM   #2
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Yes, the curve is built into a mechanical distributor, so you don't have to worry about 2 & 3. Initial (or "base") timing is set with the engine idling low enough NOT to trigger the mechanical advance, and with the vacuum advance blocked off. To make that setting on a hodgepodge or worn engine, use a vacuum gauge instead of a timing light. It compensates for all engine conditions.

http://www.users.bigpond.com/ergoff/vac1.htm
http://www.secondchancegarage.com/public/186.cfm

Once you have it set, check it with a timing light before reconnecting vacuum just to see where it is. It should be 6-12BTDC.
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I'll bear with you, but if you're gonna get bare, you can do it alone!

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Old 10/08/10, 01:16 PM   #3
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1. its not unsual for TDC to be off a little wear in the timng chain or just mass produced parts can be slightly off. Not sure what you mean by common TDC to start but a common intial timing setting is as was said 6-12 degrees BTDC.
2. Total timing is figure by taking the intial timing, mechanical timing and vacuum advance and adding it all together. I usually dont use vacuum advance numbers as they tend to just fill the gap until your mechanical advances catches up but thats just my take on it it works for my engines..
Your dist should have numbers marked on the weights or advance stops inside it. Common number would be like 12. So you take that number and multiply it by 2 as it doubles at the crank so you have 24 degrees of mechanical advance at the crank add it to your intial timing say 12 degrees and you get 36 degrees total timing. SBF engines usually like 34-38 degrees total timing.
Basically you want all your timing in by 3000 RPM to do this you may need lighter advance springs to get it to advance faster. Also you may need to change the advance stop setup most dizzy have at least 2 different advance postions to get more or less total timing depending on your needs.
keep in mind you dont want the engine to ping if it pings you need to take some of the advance out.

3, mechanical advances dont adjust themselfs they can only produce the curve that they are setup for so either advance springs or weights need to be changed to affect the curve.

73 Ranger 2 1/2 lift 302 TFS heads NP435,PS,PDB, tierod over, 33x10.50x15 BFG M/T
71 Sport 63,000 miles all orginal except for cut fenders 302 3sp 4.11's D44/BBTrac lok rear
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Old 10/08/10, 01:52 PM   #4
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I don't have a vacuum advance on my dizzy, so only mechanical I guess.

I am a little confused- I was thinking I was having trouble getting it started because I had the rotor pointed to #1 with the crank at 0 degrees when the crank needed to be at 6-12 BTDC- but if I am reading what you guys said correctly, it should be right at 0 degrees before startup and it would advance to 6-12 at idle?

As far as the advance springs, the dizzy was setup for the current motor and the only thing that has changed is the serpentine setup so I should be okay with what I have?
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Old 10/08/10, 05:12 PM   #5
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Once the timing is set ie intial timing it doesnt change thats where your vehicle starts and idles at. If its to far advanced it will be harder to start. Same can be true if its to retarded. If your timing changes at idle speed then either your advance springs are to light or idle speed is to high. Usually when you go past 12 degrees initial timing the engine cranks slower and is hard to start. Every engine is a little different so 12 is just kind of a general number in my experiance.

Just looking at where the rotor is compared to TDC doesnt mean much unless your using a timing light and its showing that you have your timing set to TDC.

For the most part the advance springs you have should be fine most aftermarket dizzy's come with a good curve if you were really into tuning then you can change the curve to possibly get some more power. At this point I wouldnt worry about it. Until you get the basic tuning down pat.

73 Ranger 2 1/2 lift 302 TFS heads NP435,PS,PDB, tierod over, 33x10.50x15 BFG M/T
71 Sport 63,000 miles all orginal except for cut fenders 302 3sp 4.11's D44/BBTrac lok rear
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Old 10/08/10, 06:44 PM   #6
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I finally got it started, I had all my plug wire sequence running clockwise (dumbass) and once i fixed that sure as shit she started right up. I hit it with the timing light and I am currenty retarded (ATC?) a few degrees.

I am trying to set the intial timing now, starting at 12 BTDC. It still won't idle very well. Do you just retard and advance until you get a consistant idle? I can't keep the truck running at anything less than 1000-1200 rpm, is this an okay RPM to set the initial timing?

Last edited by Bundy; 10/08/10 at 07:10 PM..
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Old 10/08/10, 11:42 PM   #7
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Usually most mechanical advances start advancing right around 1000 RPM. You can get it running then adjust your carb so it runs better and lower the idle speed. Then adjust timing again.. You may have to adjust the carb again when you reset the timing as changes in timing setting can affect fuel mixture requirements.
If you find that you cant get it to idle any lower then I would suspect you have a vacuum leak.

73 Ranger 2 1/2 lift 302 TFS heads NP435,PS,PDB, tierod over, 33x10.50x15 BFG M/T
71 Sport 63,000 miles all orginal except for cut fenders 302 3sp 4.11's D44/BBTrac lok rear
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Old 10/09/10, 09:25 AM   #8
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1000RPM is too high. Work on lowering the idle. You need it well below 900; preferably around 750. Don't worry about where the timing is - use the vacuum gauge to set it. Once it's set, then use the timing light to find out where you put it.

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