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PontiacFighter 05-01-2012 06:30 AM

Pontiac timing
 
Hi there, I'm trying to break in a motor that I just built. It's a 1975 Pontiac 400. I have fire at the spark plugs but the motor will not crank. I had the motor to breifly crank but it had an electronic advance distributor in it and it would not run long. I replaced it with a correct vacuum advance distributor and I do have fire but it's not cranking. The motor will only turn over. I believe it's either a lack of gas or the timing is off. When setting the dist. I got the #1 cylinder on TDC and put the rotor button in toward the steering wheel of the car ( about 1 O'clock), then I put the #1 wire to the left of the rotor and wired Counter-clockwise. While trying to crank it I turned the dist. but it didn't seem to respond to any adjustments. Can anyone tell me what might be wrong?

Mr. P-Body 05-01-2012 07:48 AM

"TDC" occurs twice in the cycle. One is on "compression", the other, "overlap". If you didn't "blow" #1 (hold a finger on the spark plug hole while cranking until it "blows" your finger off the hole), you're not certain which TDC you're "at". You must be on "compression" for timing purposes.

You must also verify you HAVE fuel in the carb. Usually, operating the throttle will tell you, by watching for the accellerator pump "squirt".

Once #1 is established and you KNOW you have fuel and spark, use a socket to turn the crank (15/16" deep works well) set the timing mark on "12" (on the cover). Turn the key "on" and rotate the distributor back and forth, with #1 wire removed and held NEAR "ground". It will arc a spark when it hits the trigger. THAT is where you want to "start your search for the "happy spot". Often, "rocking" the distributor back and forth will get it VERY close.

"By the book", #1 terminal is at ABOUT 7 o'clock when sitting in the driver's seat. I don't think it really matters, but for consistency, we try to follow that.

NOTE: The term "cranking" means the engine turns over, not necessarily "firing". If an engine "cranks", it means the starter circuit is working. For clarity.

Jim

cobalt327 05-01-2012 09:04 AM

Quote:

Originally Posted by PontiacFighter
Hi there, I'm trying to break in a motor that I just built. It's a 1975 Pontiac 400. I have fire at the spark plugs but the motor will not crank. I had the motor to breifly crank but it had an electronic advance distributor in it and it would not run long. I replaced it with a correct vacuum advance distributor and I do have fire but it's not cranking. The motor will only turn over. I believe it's either a lack of gas or the timing is off. When setting the dist. I got the #1 cylinder on TDC and put the rotor button in toward the steering wheel of the car ( about 1 O'clock), then I put the #1 wire to the left of the rotor and wired Counter-clockwise. While trying to crank it I turned the dist. but it didn't seem to respond to any adjustments. Can anyone tell me what might be wrong?

When you say you put the #1 wire to the left of the rotor (or positioned CCW from the rotor), to ME that means you have the timing retarded and actually have the timing set ATDC not BTDC- because the distributor on a Pontiac rotates CCW.

PontiacFighter 05-01-2012 01:45 PM

Yes the motor is at TDC compression stroke. But I was told to put the timing mark on the balancer at 0, not 12.

cobalt327 05-01-2012 02:13 PM

Quote:

Originally Posted by PontiacFighter
Yes the motor is at TDC compression stroke. But I was told to put the timing mark on the balancer at 0, not 12.

Correcting that will likely allow it to run if everything else is in order (like the valves being adjusted correctly and the carb primed- which after all the cranking, it should be).

If you have cranked this engine over repeatedly, the lube that should have been applied to the cam lobes is largely wiped off. That happens as soon as the engine fires anyway, but at the very least, be sure there's sufficient ZDDP in the motor oil to provide the high pressure lube the cam and lifters need at start up.

Good luck. :thumbup:

PontiacFighter 05-01-2012 03:32 PM

Ok so the timing mark must be at 12? Or can I start the motor with the mark 0?

cobalt327 05-01-2012 03:48 PM

Quote:

Originally Posted by PontiacFighter
Ok so the timing mark must be at 12? Or can I start the motor with the mark 0?

What matters is that the ignition is advanced about 12-14 degrees. Most guys find it easier to estimate the timing by using the timing marks/damper line to indicate 12-14 degrees and aligning the rotor directly w/#1 terminal than they do guessing at how much distributor rotation it takes to give you about 12-14 degrees BTDC with the damper line indicating zero (TDC).

PontiacFighter 05-01-2012 04:06 PM

So if I put the damper line at the 12 degree line on the timing cover the motor will start?

cobalt327 05-01-2012 04:35 PM

Quote:

Originally Posted by PontiacFighter
So if I put the damper line at the 12 degree line on the timing cover the motor will start?

With the damper line set to 12 degrees BTDC on the cover, if the rotor is aligned to point directly at the #1 terminal of the cap with the engine on compression for #1 cylinder, it will start- providing all else is in order as I already mentioned.

To align the rotor:

Mark the distributor body to show where #1 terminal is on the cap
Loosen the distributor clamp
Turn the distributor until the rotor is pointing at the mark on the distributor body
Replace the cap and snug the clamp, but not so tight that you can't adjust the distributor

Everyone has their own way of doing things; one way of doing this is once the engine fires, set the timing to give you about 34 degrees BTDC at 2000 rpm. This will be enough timing to let the engine break in w/o overheating from retarded ignition timing. It may still get hot- but it won't be caused by the timing. You can position fans in front of the grill to help cool it. If it starts to overheat, stop the engine and cool it down before doing the rest of the break in.

If you don't have a dial back timing light, MAKE A TIMING TAPE to see what the total timing is, w/o needing a dial back light. You can also buy a timing tape, get one that matches the diameter of your damper.

The image shows the correct orientation of the timing tape:
http://ecx.images-amazon.com/images/...500_AA300_.jpg

PontiacFighter 05-01-2012 05:13 PM

Ok thank you. I'm not discounting your advice, I greatly appreciate it but I have someone who has been working on Pontiacs for a long time and he told me to set the mark at 0 on the balancer. Why would he tell me to do that if it was wrong? And if I crank it with the 12 degree setting will I have to change it to keep it running?

cobalt327 05-01-2012 05:21 PM

Quote:

Originally Posted by PontiacFighter
Ok thank you. I'm not discounting your advice, I greatly appreciate it but I have someone who has been working on Pontiacs for a long time and he told me to set the mark at 0 on the balancer. Why would he tell me to do that if it was wrong? And if I crank it with the 12 degree setting will I have to change it to keep it running?

If you were able to get it to start when set at zero degrees, then fine- but if I understood the posts you've made, the engine did not want to run at zero timing.

Do this- ask your guy how much timing to start the engine with, and how much timing to run it at while it breaks in. I think there may be a disconnect between his instructions to you and your understanding of those instructions.

cobalt327 05-01-2012 05:27 PM

Also, if the engine wasn't trying to run at all with the 'new' distributor, I'd want you to take another look at EVERYTHING, especially that #1 is on compression and that the lifter preload is correct.

PontiacFighter 05-01-2012 06:39 PM

The only time the motor has started was when it had an electronic advance dist. in it. The motor cranked for about 2 seconds then it died and smoke came out of the carb. I was told to replace it with a vacuum advance because the electronic wouldn't allow to rev correctly. But this vaccum has fire but still no combustion. And I do have gas.

GMCBEAST 05-02-2012 02:23 PM

Is it possible when reinstalling, the plug wires were not installed right? As mentioned before Pontiac's timing is counter clockwise. Firing order is the same as Chevy I believe which is 18436572, with #1 being (while facing motor) on front right with 3,5,7 behind it and #2 on left with 4,6,8 behind it. Distributor sits on opposite side of cam gear than Chevy so it spins counter clockwise. Just something you can check out, hope it helps.

GMCBEAST 05-02-2012 04:31 PM

Quote:

Originally Posted by GMCBEAST
Is it possible when reinstalling, the plug wires were not installed right? As mentioned before Pontiac's timing is counter clockwise. Firing order is the same as Chevy I believe which is 18436572, with #1 being (while facing motor) on front right with 3,5,7 behind it and #2 on left with 4,6,8 behind it. Distributor sits on opposite side of cam gear than Chevy so it spins counter clockwise. Just something you can check out, hope it helps.

Sorry, forgot to mention plug wires go back on distributor counter clockwise, for some reason it wouldn't let me edit my post.


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