Hot Rod Forum : Hotrodders Bulletin Board - View Single Post - Rebuilding found 68' GTO Timing Problems
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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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