Timing help

[bucata206]

I'm going to try to check the timing on my 350 tomorrow in my 79 K10. I have never done this before and see lots of posts online about setting the initial timing, but not much on checking the timing with an older motor.

The motor sounds like it has a misfire from time to time and has what sounds like a top end rattle at high RPMs. Was wanting to start with checking the timing (and changing the plugs) to see if this takes care of the issue. That being said, I do have an old timing light that used to belong to my dad. Is someone able to give me a crash course on how to do the timing? Not even sure where the timing light connects or what I'm looking for.

If it is too much to explain I can try to take it to someone to have it done, but I'm really wanting to try to do things with the truck myself.

Thank you in advance!

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[rich weyand]

Timing is trivial. It's basically just a strobe light triggered by the engine spark signal.

The timing light is going to have two clips, sort of like jumper cable clips but smaller, one red and one black. Those clip on the battery. The other wire will either have an inductive pickup, which is a plastic clip that clips around the number 1 spark plug lead (driver's side front), or a spring doodad that connects between the #1 spark plug and the spark plug wire. Warm up the engine first, then hook all this up with the engine off. Make sure the timing light is secure somewhere and the wires are dressed out of the way of the fan and belts. Disconnect the vacuum advance hose between the carb and the distributor -- everyone will tell you to plug it, but no need. Now start the engine. The timing light will be flashing. You may have to hold an "on" button. Shine the light down at the wheel on the front of the crankshaft (without getting anything caught in the fan or belts! Careful there!). You should see a saw-tooth-edged plate fixed to the engine, and a set of marks on the timing wheel on the crank. One saw-tooth gap will be highlighted, or marked '0', or have a mechanic's mark with a highlighter or something to set it apart. See where that hits the marks on the wheel. Probably around 6 or so before the matching zero on the timing wheel, which is a pretty stock set-up. To set the timing, (first you turn off the engine! then) you release the clamp that holds down the flange on the bottom of the distributor, then rotate the distributor very little either way, CW from the top for retard (less timing, smaller number) and CCW from the top for advance (more timing, bigger number). Tighten the clamp a little to keep it from moving, start the engine, and see what you have. Repeat. When it is where you want it, clamp the distributor down hard.

OK, so what should the timing be? Timing sets the spark so the expanding flame front/pressure wave of the burning fuel hits the piston at the right moment to get the maximum push on the piston. If it gets there a bit late, no harm done except less power and mileage. If it gets there too early, it will try to push the piston down while it is still coming up and will detonate; you get a banging or pinging sound, called knocking. Not good, and very hard on rings, rod bearings, etc. So the factory setting is conservative because you might get some bad gas that burns faster (octane slows the burn rate), and they don't want to have to give you a new engine under warranty.

That said, the more advance you set without knocking, the more horsepower and torque you get, and the better gas mileage you get, because you are at the optimum point to use the energy in the charge. Small blocks like 36* of TOTAL timing, which is base timing (what you set with the timing light) plus the mechanical advance, which is about 20* on the stock distributor. So 16 is a good number to set with the timing light. The (now geezer) hot rod boys will tell you to advance the timing a bit at a time until, when you try to accelerate from a stop on a steep hill, you start to get knocking, then back the timing off two degrees from whatever that is. You shouldn't get knocking on most stock engines with decent regular gas until about 20* BTDC.

So I just set mine at 17* BTDC, and tried it there. No knocking. Good enough.

 

[rich weyand]

Here's what the stock setup will look like:

You must be registered for see images attach

I added a timing wheel behind my crankshaft pulley so it would have more marks and be easier to read:

You must be registered for see images attach

 

[CBidzinski2010]

I know you aren't really looking to be directed elsewhere, but I too was curious about timing. If you get on YouTube and look up adjusting timing for small block Chevy, a guy does a video on a corvette with a 350 that was very useful, there is also one on there by MSD ignition that explains it in a little more detail, however, that detail is really only useful for changing the curve of the ignition advance which most vac advance dists do not do.

 

[rich weyand]

The stock distributor curves work just fine for most engines. And an adjustable one can be a PITA to get even decently right if you don't have setup equipment to see what is really going on. A lot of people, based on what I see on the forums, end up worse off than if they just got a stock distributor and ran with it.

 

[bucata206]

Thank you for the replies! Sounds fairly straight forward! I'm hoping to try it later today when I get home for work, or tomorrow.

 

[bucata206]

I know you aren't really looking to be directed elsewhere, but I too was curious about timing. If you get on YouTube and look up adjusting timing for small block Chevy, a guy does a video on a corvette with a 350 that was very useful, there is also one on there by MSD ignition that explains it in a little more detail, however, that detail is really only useful for changing the curve of the ignition advance which most vac advance dists do not do.

I will definitely look that up on youtube later!

 

[87scotty]

Good post rich

 

[bucata206]

Timing is trivial. It's basically just a strobe light triggered by the engine spark signal.

The timing light is going to have two clips, sort of like jumper cable clips but smaller, one red and one black. Those clip on the battery. The other wire will either have an inductive pickup, which is a plastic clip that clips around the number 1 spark plug lead (driver's side front), or a spring doodad that connects between the #1 spark plug and the spark plug wire. Warm up the engine first, then hook all this up with the engine off. Make sure the timing light is secure somewhere and the wires are dressed out of the way of the fan and belts. Disconnect the vacuum advance hose between the carb and the distributor -- everyone will tell you to plug it, but no need. Now start the engine. The timing light will be flashing. You may have to hold an "on" button. Shine the light down at the wheel on the front of the crankshaft (without getting anything caught in the fan or belts! Careful there!). You should see a saw-tooth-edged plate fixed to the engine, and a set of marks on the timing wheel on the crank. One saw-tooth gap will be highlighted, or marked '0', or have a mechanic's mark with a highlighter or something to set it apart. See where that hits the marks on the wheel. Probably around 6 or so before the matching zero on the timing wheel, which is a pretty stock set-up. To set the timing, (first you turn off the engine! then) you release the clamp that holds down the flange on the bottom of the distributor, then rotate the distributor very little either way, CW from the top for retard (less timing, smaller number) and CCW from the top for advance (more timing, bigger number). Tighten the clamp a little to keep it from moving, start the engine, and see what you have. Repeat. When it is where you want it, clamp the distributor down hard.

OK, so what should the timing be? Timing sets the spark so the expanding flame front/pressure wave of the burning fuel hits the piston at the right moment to get the maximum push on the piston. If it gets there a bit late, no harm done except less power and mileage. If it gets there too early, it will try to push the piston down while it is still coming up and will detonate; you get a banging or pinging sound, called knocking. Not good, and very hard on rings, rod bearings, etc. So the factory setting is conservative because you might get some bad gas that burns faster (octane slows the burn rate), and they don't want to have to give you a new engine under warranty.

That said, the more advance you set without knocking, the more horsepower and torque you get, and the better gas mileage you get, because you are at the optimum point to use the energy in the charge. Small blocks like 36* of TOTAL timing, which is base timing (what you set with the timing light) plus the mechanical advance, which is about 20* on the stock distributor. So 16 is a good number to set with the timing light. The (now geezer) hot rod boys will tell you to advance the timing a bit at a time until, when you try to accelerate from a stop on a steep hill, you start to get knocking, then back the timing off two degrees from whatever that is. You shouldn't get knocking on most stock engines with decent regular gas until about 20* BTDC.

So I just set mine at 17* BTDC, and tried it there. No knocking. Good enough.

So just to clarify. When setting my ignition timing with the timing light and motor at idle, should I set it at 16* BTDC to be safe?

 

[rich weyand]

So just to clarify. When setting my ignition timing with the timing light and motor at idle, should I set it at 16* BTDC to be safe?

To be safe, set it at 12. But your best performance and mileage will be at 16 or 17, as long as you don't get knocking. A more or less stock engine with decent regular gas shouldn't knock below 20.

 

[rich weyand]

Good post rich

Thanks.

 

[rich weyand]

So just to clarify. When setting my ignition timing with the timing light and motor at idle, should I set it at 16* BTDC to be safe?

And don't forget to disconnect the vacuum advance hose....

 

[bucata206]

Great thank you!

 

[bucata206]

So I went to do the timing today. I started out with the hash mark at TDC. When I started the truck and used the timing light, I initially could not see the hashmark anywhere near the timing plate. As I moved the distributor, I got it down to 16* BTDC and it ran rough and idled super low. I go it to 12* BTDC and the truck was barely able to run. I tried to keep it at 12* BTDC but when I would give the truck any gas, it would die. I moved it back to roughly 18* BTDC and it still did not run well, low rough idle, but I was able to get it moved back into the garage for the night.

Any idea why it was running better when the hash mark was no where near the timing scale and wouldn't keep running at 12* BTDC? I'm at a loss as I was expecting it to idle lower but run and sound better. I was also expecting the hashmark to be closer to the timing marks to begin with.

 

[firebane]

Time to confirm TDC. This can be done a few ways but the easiest way I found was pull plug #1 and then stuck a piece of wire around 12-14g in the hole.

Rotate the crank using the crank pulley bolt and when you feel the wire compress you should relatively be neat TDC; you do not need to use a lot of pressure here. At this point the groove in your balancer should be on or near the zero mark on the timing tab.

If there is a huge discrepancy then your harmonic balancer could have slipped or the wrong timing tab was used.

Once you verify TDC you can also confirm proper distributor alignment.