[CLB1098]

I just finished a rebuild and clean up on my 68 GTO. It is a 400 with #16 heads. I had the heads rebuild with hardened seals and replaced all the gaskets. While it was apart I also replaced the timing chain and gears. The plugs, wires, cap, and rotor are new and everything was assembled correctly...or so I think!! I took the time to check and recheck everything before assembly.

I attemped to start it tonight with no luck. At first I was getting a backfire through the carb and thought the distributor might be 180 off so I turned it around and it sounded like a shotgun going off. The neighbors were not too happy with that!! I lined up the timing marks to try to get it as close to TDC as possible and aligned the distributor and still no luck. It turns over fine but I am getting blow back from through the car and a couple backfires. What am I missing here? Am I that far off with the timing? I turned it over a lot with no luck or stutter like it was going to start. I gave up for tonight but am looking for some ideas to start fresh with. The car ran great prior to disassembly so this isn't making much sense to me.
Thanks for any ideas!!

[68gtoMN]

First of all, how did you align the timing marks on the gears? Were they pointing toward each other? Where does your vacuum advance canister point? How tight are your valves? Did you double check your firing order on the distributor cap? 1-8-4-3-6-5-7-2. Look at the center two on each side to ensure you have them in the right spot.

[David Jones]

Find TDC on the number one cylinder. Put your finger over the #1 spark plug hole and have a friend manually spin the engine over until you feel your finger PUFF off the hole. What's the rotor pointing to on the dist cap? #1 I hope? If not put the number one wire where it's pointing and adjust the other wires as needed to follow the correct Pontiac CCW firing order.
If that doesn't fix it the problem will be a little harder to correct........

[CLB1098]

I originally wasn't planning on replacing the timing chain and gears but when I took off the timing cover to replace the gaskets it was a little loose. Fortunately the marks were both at 12:00 so it made it easy to realign the gears. I am certain it is correct...well almost certain now!!
The vacuum canister is pointing towards the passanger/passanger door. This is near the same alignment as before disassembly. Before I left town this morning I checked the wires again and they are correct. L
I did not rebuild the heads myself. I took them to a specialist here in Phoenix and spent the money to have it done right so they should be fine.
One of the other things I thought of is my first attempt at start up. The distributor ground wire was not connected the first few attempts starting. Could flooding/fouled spark plugs be part of the issue? After realizing the distributor was not grounded and the backfire I lined up the timing marks and checked the location of the rotor and it was close to #1, close enough for it to start I would think.
Thanks for your help. I haven't had an issue like this in the past and I hope I am over thinking it and missing something simple.

[gto4evr]

Originally Posted by CLB1098

I originally wasn't planning on replacing the timing chain and gears but when I took off the timing cover to replace the gaskets it was a little loose. Fortunately the marks were both at 12:00 so it made it easy to realign the gears. I am certain it is correct...well almost certain now!!
The vacuum canister is pointing towards the passanger/passanger door. This is near the same alignment as before disassembly. Before I left town this morning I checked the wires again and they are correct. L
I did not rebuild the heads myself. I took them to a specialist here in Phoenix and spent the money to have it done right so they should be fine.
One of the other things I thought of is my first attempt at start up. The distributor ground wire was not connected the first few attempts starting. Could flooding/fouled spark plugs be part of the issue? After realizing the distributor was not grounded and the backfire I lined up the timing marks and checked the location of the rotor and it was close to #1, close enough for it to start I would think.
Thanks for your help. I haven't had an issue like this in the past and I hope I am over thinking it and missing something simple.

okay, first off, it doesn't matter where the vac advance is pointing now because if you pulled it out during the rebuild, it's indexed to where it felt like depending on where the rotor shaft was pointing when you put it back in if you didn't have the motor at TDC and try lining up the rotor as it went in to where #1 traditionally is. Secondly, I'm assuming you're still running points so I'm not sure what you mean by the distributor ground wire. The wire coming off the distributor should be connecting to the coil, not ground. Are you just twisting words there because it's connecting to the negative side of the coil?

also, don't be confused by the timing dots on the sprockets being both at 12 oclock vs facing each other (12 and 6) -- I agonized over that for years since depending on what year service manual you're using, it will say one or the other -- technically they're the same thing since the crank turns twice for every turn of the cam. So having the rotor point at the correct #1 wire on your distributor with the timing mark at 0 doesn't mean you're not off 180 degrees. Are you sure you have the firing order running counter clockwise? Next thing to check is the coil ground. It grounds through the bracket to the intake so if you've got nice new paint on your fresh motor with painted intake, coil and brackets, you may not have a good ground on the coil. Have you confirmed you're getting a spark?

[CLB1098]

gto4Evr,
Sorry about the confusion with the ground wire from the distributor. I do have it connected to the neg side of the coil. I also agree with you on the timing marks. I have heard both ways to install the gears and really don't see the difference as long as they are lined up correctly.

I am certain that plug wires are installed correctly and the alignment of the distributor is correct. I had a friend helping me last night and he confirmed that there was spark. But now that you mention it, I'm not sure how well the coil is grounded or how well he secured it after connecting the wires...which is why I don't usually let people help! Everything does have a fresh coat of paint on it so that may be it. I will check first thing when I get back into town tomorrow.
It may be something simple like I thought after all...
Thanks

[LPete]

Quick point -- the coil doesn't need to be grounded. Neither winding grounds through the case. The high-voltage winding actually connects internally to the + terminal.

[gto4evr]

Originally Posted by LPete

Quick point -- the coil doesn't need to be grounded. Neither winding grounds through the case. The high-voltage winding actually connects internally to the + terminal.

I beg to differ on that one, I had issues with my 69 not starting and found the bracket loose where the coil clamped to the accelerator cable. With someone cranking it, twisting the bracket back and forth let it light up. It happened on a few occasions until I got around to tightening the bracket.

I guess that could be coincidence since I don't claim to be all knowing but.....

[LPete]

Here's a '69 GTO coil diagram. I wouldn't say they NEVER ground the high-voltage winding, but I've never heard of it. I *think* one reason is to allow the battery to absorb electrical noise from the ignition system. I've made a few coils spark sitting on the ground...

[John Milner]

Do you have your distributor clamp fairly tight? I have had them not fire because that clamp wasn't tight causing the distributor to not ground.

[getmygoat]

Another way to verify timing - While cranking have someone advance the timing until the motor slows down, now back it off until it starts. - This is after you've verified your not 180 out with the puff/finger trick mentioned earlier.

[65WJ]

remember pontiac distributors rotate counter clockwise.

Barry White found out. that was funny.

patrick

[CLB1098]

Thanks everyone for the help. Got home yesterday afternoon and checked everything again and it started just fine. Maybe it was ground, maybe not. Either way it runs great and that's all that matters!!!