Timing Light Question

[retselgerg]

just curious on how to use a timing light and a vacuum gauge, if possible break it down to retard language lol. id like to dail in the ole pick em up
-G.Lester

[cdowns]

you buy them and read the instruction book that is in the box//thats about as basic as it gets

[HoupPhotography]

Originally Posted by cdowns

you buy them and read the instruction book that is in the box//thats about as basic as it gets

If you need that much direction, it may be better to take it to a shop.

[retselgerg]

well i have the tools, i can tune one by ear i would just like to learn how to properly use the guage and light.... and i always like things broke down as simply as possbile becoz it cuts down on repeat questions...

[HoupPhotography]

Originally Posted by retselgerg

well i have the tools, i can tune one by ear i would just like to learn how to properly use the guage and light.... and i always like things broke down as simply as possbile becoz it cuts down on repeat questions...

If you can actually "tune" a motor by ear, you don't need to use either of the tools you asked about. There are a ton of motor builders out there that can't tune a motor by ear, they can get close.... however close & luck doesn't actually "tune a motor.

No disrespect, but tuning by ear because you were lucky once and the motor ran ok doesn't count. If you can tune a motor by ear you have probably built a few motors or have been around folks that have, if you can build a motor then connecting a timing light and pointing it at the harmonic balancer should be common sense or fairly easy to figure out.

There really isn't anything to "break down" on using a timing ight.

[oldspowered67C10]

If you have a regular(non-dial back) timing light all you can really do is check idle timing and unless the engine is totally stock the factory spec isnt likely the best setting. You can use it to check total timing (what you really want to set)if you put degree tape on the balancer but youre really better off with a dial back type light.

Use of the timing light is pretty straight forward, hook up the power leads to the battery, clamp the inductive pick-up on the #1 cylinder spark plug wire and point the gun at the timing tab on the timing cover. When the light fires look for the mark on the balancer and see where it is in relation to the timing tab, that will show you how far advanced/retarded the spark timing is under the current conditions.

As far as the vacuum gauge goes, all youre really going to want to do is use it to set idle mixture. Basically you set youre idle speed then mess with the idle mixture screws until you get the highest possible vacuum reading then readjust idle speed and repeat the process until you have the highest possible vacuum reading. That will give you close to lean-best idle and will provide easy start up and nice idle/off-idle driveability.

[piecesparts]

Originally Posted by oldspowered67C10

If you have a regular(non-dial back) timing light all you can really do is check idle timing and unless the engine is totally stock the factory spec isnt likely the best setting. You can use it to check total timing (what you really want to set)if you put degree tape on the balancer but youre really better off with a dial back type light.

Use of the timing light is pretty straight forward, hook up the power leads to the battery, clamp the inductive pick-up on the #1 cylinder spark plug wire and point the gun at the timing tab on the timing cover. When the light fires look for the mark on the balancer and see where it is in relation to the timing tab, that will show you how far advanced/retarded the spark timing is under the current conditions.

As far as the vacuum gauge goes, all youre really going to want to do is use it to set idle mixture. Basically you set youre idle speed then mess with the idle mixture screws until you get the highest possible vacuum reading then readjust idle speed and repeat the process until you have the highest possible vacuum reading. That will give you close to lean-best idle and will provide easy start up and nice idle/off-idle driveability.

Good info but look at what type of engine you may be working on---there are some (not in the GM world), that time off of a different plug other than good old #1. International comes to mind.

[straitnate14]

well you hook your vacum light up to your number one plug wire, with the engine running you point it down at the balancer and look for your timming marks if you can see them great if not sucks to be you , I think I'm set at around 12 advanced with no vacum advances since I'm running a blower, call summit and ask them what they think you should start with, and vacum, your looking to get as much at idel as you can I think I got around 20 at idel and it stays solid as a rock grab someone who has done it before and have them teach you how about 2 months ago I would be asking how to do it but you learn it qick after 2 or 3 times. turn the base of the distributor until you go the way you want and lock it down when your done

[LONGHAIR]

well you hook your vacum light up to your number one plug wire, with the engine running you point it down at the balancer and look for your timming marks if you can see them great if not sucks to be you

You are kidding right?
Please try to be helpful, sarcasm is not helping anyone.

[Billla]

I think folks are making this too hard Retselgerg, I give you major props for wanting to learn this. It's not hard at all, and it's a great skill to have. "Tuning by ear" will almost always give too much initial advance.

Maybe we can tweak this as a group and make a FAQ.

To set base timing - timing without mechanical or vacuum advance - follow the steps below. Note that I agree that you should get the service manual for your truck - you'll need it. And this is only for our 67-72 trucks, as noted there are differences for other years. Finally, if you're looking to set performance timing by adjusting the mechanical and vacuum advance - that's a different topic.

Setting Idle Mixture

1. Bring the engine to operating temperature with a short drive.
2. Set the idle speed to the correct setting per the service manual
3. Turn the idle screws GENTLY all the way in, counting the turns, then turn them back to their initial setting. If they're not the same, then use the richest (furthest out) setting for both.
4. Connect your vacuum gauge to a "ported" or "timed" vacuum source on the carb - this is a vacuum connection that is ABOVE the throttle butterflies
5. Turn one screw in 1/4 turn and note the change - if the vacuum rises, then turn the other idle screw in 1/4 turn and again check the gauge. As long as the vacuum continues to rise, turn the scews in, alternating them. If the engine stumbles, turn both screws out 1/4 and call it good. The idle screws should be set to the number of turns.
6. Readjust idle to correct speed.

Setting Base Ignition Timing

1. If this is a points distributor, point gap/dwell must be set before timing.
2. Find the timing tab and the Top Dead Center (TDC) marking on your front cover and harmonic balancer. It helps sometimes to use a china marker or chalk on the TDC marking to make it easier to see.
3. Look at the timing tab and be sure you understand the marks. Yourr service manual will give the correct timing, generally 8-10 degrees Before Top Dead Center (BTDC). Find the corect mark on the timing tab and mark that with your china marker or chalk.
4. Disconnect the vacuum advance at the distributor and plug it - a golf tee works very well for this This is to prevent vacuum advance at idle.
5. Loosen the distributor hold-down such that the distributor can turn - not loose, but loose enough
6. Connect the timing light pickup to the #1 spark plug (first on the right side) as close to the plug as possible. Connect the pos/neg leads of the timing light to the battery, careful to avoid the fan.
7. Start the engine and carefully - always aware of the fan - point the timing light at the timing tab. What we're looking for is to turn the distributor until the marks on the harmonic balancer and the timing tab line up - it's that simple.
8. Once that's complete, tighten the distributor hold down being careful not to disturb the setting, reconnect the vacuum advance and disconnect the timing light.

[c10crazy]

The first 2 responses were so darn informative!

[chevy72blu]

Thanks to the guys that responded with info - especially Billla! I have never owned a light or vac gauge (I have always just done it by ear, also, but, I plan on buying a light to tune my BBC when I finally get home to fire it. Thanks!

[Billla]

Originally Posted by chevy72blu

I plan on buying a light to tune my BBC when I finally get home to fire it.

Spend a little extra money and buy one with advance capability; it'll be worth it for tuning the advance curve!

[BarryB]

But I have a question now. What if your motor isn't stock? running a different cam? How do you get the timing setting then? I have always done it by ear, when this was the case. But I would definately be inclined to listen to everybodies tricks.

[68GMCCustom]

Spend a little extra money and buy one with advance capability; it'll be worth it for tuning the advance curve!

[Billla]

Originally Posted by BarryB

But I have a question now. What if your motor isn't stock? running a different cam? How do you get the timing setting then? I have always done it by ear, when this was the case. But I would definately be inclined to listen to everybodies tricks.

I put my timing FAQ back up. Everything you need to know is there.

Not to beat a dead horse, but you CANNOT time an engine by ear, period. It will always end up too far advanced - it may run OK, but it's not returning it's best driveability, fuel economy or power.

[retselgerg]

lots of good info, for the record the engine is a stock 260hp crate engine with less then 300 miles on it, and although this may be a pretty straight forward thing for most folks im different. I dont like to do stuff at a mediocore level, i like to master them i figure that if they can make a science out of bottling water then i can make a science out of most anything i attempt. Thanks for the info i now believe i can handle the tuning task.
thanks
G.Lester

[Billla]

Originally Posted by retselgerg

tuning by ear will you get close but not dead on

I'll place $20 on the hood for anyone that can get "close" by ear. I've never tuned one that's been tuned "by ear" that didn't have 16+ degrees of timing at idle, because that's where it sounded "right".

Not trying to be a d*ck (really ), it's just something that's a science - not an art.

[oldspowered67C10]

But I have a question now. What if your motor isn't stock? running a different cam? How do you get the timing setting then? I have always done it by ear, when this was the case. But I would definately be inclined to listen to everybodies tricks.

Typically what I do is set total timing(vacuum disconnected/engine reved up until distributor will no longer advance)at about 36-38 advanced. If I have a adjustable advance distributor I then try to get idle at about 10-12 advanced, if its not adjustable I leave it where it is since Im more worried about total timing than idle timing. I then drive it and make any needed adjustments.

[piecesparts]

Originally Posted by oldspowered67C10

Typically what I do is set total timing(vacuum disconnected/engine reved up until distributor will no longer advance)at about 36-38 advanced. If I have a adjustable advance distributor I then try to get idle at about 10-12 advanced, if its not adjustable I leave it where it is since Im more worried about total timing than idle timing. I then drive it and make any needed adjustments.

That is how my stroker motor is set up and it is easy to start and drive. Any tuner will tell you that the advance is what works for your efficiency and economy on a motor. The motor temps are affected by timing, also. An engine will run hotter if it is lagging on it's timing. Setting an engine by ear is a shot in the dark, until you have the equipment to fine tune it.

[Billla]

Originally Posted by oldspowered67C10

Typically what I do is set total timing(vacuum disconnected/engine reved up until distributor will no longer advance)at about 36-38 advanced. If I have a adjustable advance distributor I then try to get idle at about 10-12 advanced, if its not adjustable I leave it where it is since Im more worried about total timing than idle timing. I then drive it and make any needed adjustments.

I honestly don't understand this approach - can you provide more detail?

[67_C-30]

Originally Posted by Billla

I honestly don't understand this approach - can you provide more detail?

NOTE: This kind of tuning is not neccessary for stock engines, and is not required. This is more suitable to engines that see frequent high RPM use!
Setting base timimg works well for stock engines, but total timing yields the best performance results, and is really a must for high performance engines. It works just like base timing except focusing on getting the 6 - 10 degrees at idle, you tune it by setting the timing when the distributor is at full advance usually 3000 - 3500 RPM. The TDC marks on a lot of stock (especially high mileage) balancers are dead wrong. The foolproof way to insure your mark is correct is to pull the INT and EXH rockers off #1 and screw a piston stop into the #1 hole and go all the way clockwise until it bumps the stop and lightly scribe a line at TDC on the balancer. Do the same counterclockwise and lightly scribe another line. The distance between the these 2 lines will depend on how far the piston stop extends into the cylinder. Its doesn't what the distance is, but you have to measure it with a dail calipers and split the difference, and scribe a line between them. For example, if the lines are .800" apart, set the calipers to .400" and scribe a line between them. This is the TRUE TDC mark. If its in the same location as the stock mark, you're lucky because all too often its not.


After you've determined TDC, you can use a timing light that has advance capability, so you can go old school, and put timing tape on the balancer. Again, that old-tech tape is foolproof. An after market racing balancers such as welded hub balancer or a Fluidampr already have these marks. With the advance disconnected and plugged (same as setting initial) pull the engine up in RPM increments of 1000 and you can watch and graph the full advance curve. Pull it up until it is no longer advancing which is usually between 3000-3500 sometimes even 4000. On lower compression engine you can run as much as 40* but most fall in the 36-38* range. Higher compression engines usually range in 32*-34* range. The object is to run as much timing as you can without detonation.


You can then adjust the timing curve by changing springs and weights. If the advance curve is coming in too slowly, you add lighter springs and springs if needed until you achieve the desired curve. If total is coming too quickly, just go vise versa and add heavier springs. The weight and spring kits usually come with a couple of graphs showing typical advance curves and a general guideline of what weights and springs to use, but it is what is, just a guideline. You have to check with the light because the pink or red spring doesn't always do what that graph says its gonna do!

[haysonj]

What 67 C-30 says is more for racing as total timing is only while under load. when you get to cruise speed the vacuum advance comes back in and you should now be around 50 degrees total advance. Unless you are racing you want all your advance in by 2500 RPM.Check out this post by Alaskan in FAQ http://67-72chevytrucks.com/vboard/s...d.php?t=274806

[piecesparts]

Originally Posted by haysonj

What 67 C-30 says is more for racing as total timing is only while under load. when you get to cruise speed the vacuum advance comes back in and you should now be around 50 degrees total advance. Unless you are racing you want all your advance in by 2500 RPM.Check out this post by Alaskan in FAQ http://67-72chevytrucks.com/vboard/s...d.php?t=274806

You are right and if you have changed your distributor to time in early, this works well on ths street. As I stated above, I have my stroker motor set up this way and my son's 350 in his 86 is timed to total advance numbers. It really does make the process different from setting static timing and living with it. I use this method most of the time now and have had no issues on daily driving.

[Billla]

Originally Posted by 67_C-30

NOTE: This kind of tuning is not neccessary for stock engines, and is not required. This is more suitable to engines that see frequent high RPM use!

No; I understand this - very well See my timing FAQ

I don't understand the comments about adjustable/non-adjustable and how he's approaching the curve - seems backwards. Might just be semantics...