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Old 08-03-2012, 08:57 PM
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Rebuilding found 68' GTO Timing Problems

Hello guys, My name is corey and this is my first post. Im a chevy guy at heart and this is my first Pontiac. Im 22 y/o and a senior in college for sculpture and design.

My father and I recently acquired a 1968 GTO. We think that the engine is a pontiac 400 because that is what the car is badged. We dont think we have the original block but know we have a pontiac v8. We got the car started by doing normal rebuilding methods. (changing spark plugs, rebuilding carb, etc) The engine initially ran rough, was backfiring, and didnt shut off when the key was turned off, it kept sputtering.

Rebuild

The first thing we did was replace the distibutor, coil, and spark plug wires. We bought an ACCEL distributor, wires and coil. We installed all of these and rewired one of the ignition power wires to the coil. The reason we rewired this was becasue the original coil required resisters, and a bunch of things bolted to the firewall. The original power wire we were told was a resistance wire that lowered the voltage as the current traveled through it. After all of these upgrades we were able to start the car but it still runs pretty rough. It starts up nicely but doesn't run right. When trying to time the car to fix the poor running, we would advance the time to 30 and the car runs better, but when turned off and turned back on, the engine just chugs and the distributor has to be retarded back in order to fire again. when at the recommended time of 10-12 the engine is miss firing which can be seen on the timing light and is back firing repetively.

So basically we dont know what the problem is, we think it may be the timing, or maybe the distributor is 180 out.

We got the engine to TDC by checking the height of the piston in the #1 cylinder, but we may have had it on the exhaust stroke, not the compression stroke. The rotor was pointing to #1 when the engine was timed, but we couldnt get the engine timed.

Any advice or questions about our build would be greatly appreciated.

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Old 08-04-2012, 04:01 AM
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To verify it's on the compression stroke..... pull the #1 plug, place your thumb over the hole, bump the starter or turn by hand (I bump the starter) you'll feel the compression stroke, aline the TDC marks, pop the dizzy cap and verify #1 rotor position.

When you removed all the old wires, did you leave the wire going from the pos post on the coil, down to the "I" terminal on the starter?

When the key is turned and the solenoid engages on the starter, The "I" terminal goes hot and provides 12v to the coil.... while in the start position, after it starts and the key goes to the run position, the "I" terminal goes dead and the coil gets 9ish volts from the resistance wire etc......

The new system doesn't need the resistance wire, but unless you ensured the new wire you put in was hot in start and run..... and if you didn't leave that "I" terminal wire you probably are'nt getting 12v while cranking etc....
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Old 08-04-2012, 03:05 PM
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Quote:
Originally Posted by BRNFND GTO View Post
Hello guys, My name is corey and this is my first post. Im a chevy guy at heart and this is my first Pontiac. Im 22 y/o and a senior in college for sculpture and design.

My father and I recently acquired a 1968 GTO. We think that the engine is a pontiac 400 because that is what the car is badged. We dont think we have the original block but know we have a pontiac v8.
Congratulations on acquiring your Pontiac! They're a different bird than a Chevy, but well worth the added learning curve to get to know them, IMHO.

You can take a look here for info on ID'ing the block and heads to determine if the engine you have is 'correct' for the vehicle. Here is a page w/info and sites specific to the Pontiac.

Quote:
We got the car started by doing normal rebuilding methods. (changing spark plugs, rebuilding carb, etc) The engine initially ran rough, was backfiring, and didnt shut off when the key was turned off, it kept sputtering.

Rebuild

The first thing we did was replace the distibutor, coil, and spark plug wires. We bought an ACCEL distributor, wires and coil. We installed all of these and rewired one of the ignition power wires to the coil. The reason we rewired this was becasue the original coil required resisters, and a bunch of things bolted to the firewall. The original power wire we were told was a resistance wire that lowered the voltage as the current traveled through it. After all of these upgrades we were able to start the car but it still runs pretty rough. It starts up nicely but doesn't run right. When trying to time the car to fix the poor running, we would advance the time to 30 and the car runs better, but when turned off and turned back on, the engine just chugs and the distributor has to be retarded back in order to fire again. when at the recommended time of 10-12 the engine is miss firing which can be seen on the timing light and is back firing repetively.

So basically we dont know what the problem is, we think it may be the timing, or maybe the distributor is 180 out.

We got the engine to TDC by checking the height of the piston in the #1 cylinder, but we may have had it on the exhaust stroke, not the compression stroke. The rotor was pointing to #1 when the engine was timed, but we couldnt get the engine timed.

Any advice or questions about our build would be greatly appreciated.
Hard to make a diagnosis based on just this, but my first reaction would be that the timing set may be worn excessively or may have "jumped time".

When this happens the ignition timing (being geared to the camshaft) will be off from the crankshaft position and often it takes a lot of timing advance to offset the jumped time from the worn out timing set. And in turn, the change in ignition timing needed to allow the engine to run even halfway normal will often be way off for restarting the engine- much like what you're describing.

Another page on determining TDC is here. Under "Resources" at the bottom of the page are other links to useful info.

I consider replacing the timing set to be almost a given on any engine w/an unknown history. If your research into the problem leads you nowhere, consider doing the timing set.

One last thing: The firing order is the same as a Chevy V8, but the distributor rotation is CCW (as you know). This difference invites someone used to a Chevy to get the plug wires mixed up, so be absolutely sure the cap and plugs are wired correctly.

BTW, Terminal #1 can be any terminal- as long as the piston is at TDC ready to fire (not on exhaust stroke), whatever terminal the rotor is pointing to can be #1. Often specific terminals were used by the factory and the terminal used will often differ based on whether the ignition is points or HEI.

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Old 08-04-2012, 08:04 PM
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I would recommend performing a compression test. That is the most basic and important thing to do when trying to tune/diagnose an engine.
It is a step I would not skip. Do it now.
Then, when finished, put a socket on the front crankshaft bolt. Also Loosen the distributor cap, pulling it aside exposing the rotor so you can watch it as it moves. Very important.
Next,.. Turn the engine slowly by hand, watching the timing mark on the balancer. Pull it to 0 degrees top dead center. At this point, watch the distributor rotor, turn the engine SLOWLY backwards, watching thr rotor. As soon as the rotor starts to move, look at the balncer to see how many degrees the engine turned BEFORE the rotor actually moved. If you turned it more than 12 degrees, the timing chain and gears are worn and may need replace. 12 degrees is a rough "rule of thumb" .
12 degrees or more of slack in the chain is pretty indicative of a worn chain set needing replaced.
After these 2 tests you will know which direction to go next on how to get er runnng good. I gaurantee it.
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Old 08-04-2012, 11:45 PM
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That's a good point, LATECH- and it also reminded me that I forgot to add a link to the page on checking the amount of wear.

Last edited by cobalt327; 08-05-2012 at 12:03 AM.
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Old 08-05-2012, 09:03 PM
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Thanks for all your advice guys. In the mean time I have replaced the timing set, the fuel pump and the water pump. We got it all together today and when we started it to time the engine we had the same problems. Large advance to run smoother, back firing, and wouldnt start up again with large advance. We havent tried any of the tests you guys suggested. we will try some tomorrow and i will get back to you with the results. I have a feeling that the problem wasnt the timing chain, but its good to replace as the car sat for over 10 years. We have done alot of work the past few days and havent seen very much result. We cant figure out why the engine is back firing.

The engine is running quite rich which is causing heavy carbon buildup on the spark plugs. The dist. cap popped off and bounced around a bit a few days ago. Would these things be possible cause of our problems? Would some fresh or cleaned spark plugs a new cap and rotor help us out?? Thanks again guys
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Old 08-06-2012, 03:53 AM
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Your car, your money....... but I'd stop throwing parts at it untill I found what was wrong with it. Now don't get me wrong if a parts bad... replace it, and after you get it running correctly replace all you want...... Reason being... you've not corrected the original problem but have added several areas to the possible list of what it might be....yadda-yadda....

Sounds like you got a firing order, dizzy alignment issue.
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Old 08-06-2012, 06:33 AM
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Let's not rule out a "flat camshaft".
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Old 08-06-2012, 06:36 AM
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wheres the pics. lets see the old goat !!
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Old 08-06-2012, 06:54 AM
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check compression is #1 step.
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Old 08-06-2012, 02:52 PM
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Heading out there today to do a compression test, clean all of the spark plugs, replace the cap and rotor, and advance each spark plug 1 spot counter clockwise. heres some photos of my Old Goat





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Old 08-06-2012, 03:10 PM
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Could you guys post some more info regarding the problems metioned. (flat cam shaft, dizzy alllignment etc). How would i diagnose/fix a firing order issue?
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Old 08-06-2012, 03:21 PM
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pay attention to what EOD Guy told you and give us compression reading first.
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Old 08-06-2012, 03:38 PM
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I wouldn't recommend advancing the spark plugs by one....... at TDC the rotor is in the right spot or it's not..... if it's not, re-index the dizzy until it's in the correct spot. If it runs smooth with the advanced timing etc..... doubt it's a flat camshaft.

You need to verify the rotor is at the number one position at TDC on the compression stroke. (see the diagram above) if it's not pull the dizzy out far enough to advane the gear one tooth at a time , drop back in, recheck rotor position, untill it's in the right position.

Verify you have the correct firing order.....18436572 counterclockwise.... looking from the front bumper at the dizzy (unless a 307 which is clockwise)

Verify you have 12v at the coil (dizzy if HEI) while cranking...."I" terminal from starter is the eaisest way to acomplish this
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Old 08-06-2012, 04:36 PM
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how would i go about aligning the distributor if it only drops in in 2 spots in the oil pump shaft. Meaning the flathead screw like rod that fits in the notch in the bottom of the distributor only drops the distributor in in 2 positions. How do i rotate the distributor gear until it is perfectly alligned ie one tooth at a time, if the dizzy will only drop in those two spots. Our problems seems to be that the oil pump shaft wont allow us to drop the dizzy pointing towards the #1 plug.

Last edited by BRNFND GTO; 08-06-2012 at 04:37 PM. Reason: bad wording
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