L71 rebuilt engine won't start - follow up

[Tom R.]

From not being able to start my fresh rebuilt engine - last week after taking everyone's advice, I realized today I had weak spark from only about 3 volts at the coil. Finding wiring problems and Bubba's quick fixes as I've read on here, I removed and replaced the TI coil with a cheap rebuilt from Autozone just to bypass the existing electrical problems hoping to get the engine running and broken in before losing all pre-lube. After finally finding a wire w/12 volts w/key on, I was able to get the car started but not running. Spark/voltage yes, fuel yes, compression definitely, timing horrible. We've had the distributor out at least 2 dozen times. We've tried TDC and balancer tab on 0, on 5, on 8, on 10 but still will not run. I'm 100% (okay maybe 99%) sure we're on the compression stroke. While bumping it around, it'll blow your finger way out of the hole and makes a loud hiss. The line on the balancer would normally be close to the tab and I'd turn it by hand to set it on one of the marks (tried all of them too). Inserted the distributor with rotor pointing as near to the #1 wire location as possible. I put the #1 wire just right of centerline towards the passenger side as shown in the Assembly manual and also in Chilton's repair manual. This makes the cap window near to centerline and leaves the vac in between the intake and shielding bracket. The car will start but only run for a few seconds and there's not enough adjustment with the distributor to correct so we thought we were off a tooth. Tried moving the distributor 1 tooth in both directions several times and it does not help. Even thought we might be off 180 but trying that doesn't help either. It backfires through the carb from being on the exhaust stroke. This entire process is very simple in concept but I'm out of ideas. Have checked the indexing of the wires on the cap until I can see them in my sleep. There's spark, gas, and everything needed but I cannot get it timed enough to run. The original TI distributor has the dimple on the bottom of the shaft which basically lines up with the rotor. The rebuilt temporary replacement has the same but the dimple is a little off from exactly lining up. I only mention that in case it means something with somebody. I am using the TI coil with the replacement distributor thinking that didn't matter. And I did remove the rotor from the TI distributor to use temporarily. The engine harness is somewhat of a mess and I do not know how it ran before the rebuild. I'll correct that after I get the motor running on a better day. I say in advance that I am feeling inept and am in need of help. I've read everything on here in the archives regarding reinstalling a distributor and obviously have missed something important. This has never been this difficult before.

[Joe L.]

Re: L71 rebuilt engine won't start - follow up

From not being able to start my fresh rebuilt engine - last week after taking everyone's advice, I realized today I had weak spark from only about 3 volts at the coil. Finding wiring problems and Bubba's quick fixes as I've read on here, I removed and replaced the TI coil with a cheap rebuilt from Autozone just to bypass the existing electrical problems hoping to get the engine running and broken in before losing all pre-lube. After finally finding a wire w/12 volts w/key on, I was able to get the car started but not running. Spark/voltage yes, fuel yes, compression definitely, timing horrible. We've had the distributor out at least 2 dozen times. We've tried TDC and balancer tab on 0, on 5, on 8, on 10 but still will not run. I'm 100% (okay maybe 99%) sure we're on the compression stroke. While bumping it around, it'll blow your finger way out of the hole and makes a loud hiss. The line on the balancer would normally be close to the tab and I'd turn it by hand to set it on one of the marks (tried all of them too). Inserted the distributor with rotor pointing as near to the #1 wire location as possible. I put the #1 wire just right of centerline towards the passenger side as shown in the Assembly manual and also in Chilton's repair manual. This makes the cap window near to centerline and leaves the vac in between the intake and shielding bracket. The car will start but only run for a few seconds and there's not enough adjustment with the distributor to correct so we thought we were off a tooth. Tried moving the distributor 1 tooth in both directions several times and it does not help. Even thought we might be off 180 but trying that doesn't help either. It backfires through the carb from being on the exhaust stroke. This entire process is very simple in concept but I'm out of ideas. Have checked the indexing of the wires on the cap until I can see them in my sleep. There's spark, gas, and everything needed but I cannot get it timed enough to run. The original TI distributor has the dimple on the bottom of the shaft which basically lines up with the rotor. The rebuilt temporary replacement has the same but the dimple is a little off from exactly lining up. I only mention that in case it means something with somebody. I am using the TI coil with the replacement distributor thinking that didn't matter. And I did remove the rotor from the TI distributor to use temporarily. The engine harness is somewhat of a mess and I do not know how it ran before the rebuild. I'll correct that after I get the motor running on a better day. I say in advance that I am feeling inept and am in need of help. I've read everything on here in the archives regarding reinstalling a distributor and obviously have missed something important. This has never been this difficult before.

Tom-----


First off, the slight mis-alignment of the distributor rotor contact with the "dimple" on the gear means nothing. They often do not align precisely. No big deal, at all.

Next: how did you originally adjust the valves? How did you determine TDC of the #1 cylinder when you initiated this process?

[Timothy B.]

Re: L71 rebuilt engine won't start - follow up

Tom,
Are you saying the car has TI ignition and you installed a points distributor? You can't use the harness for TI for conventional points distributor. That may explain why 3 volts for the coil, find the 12 volt pigtail from the ignition switch that plugs into the TI harness, unplug and run it through a ballast resistor then to the coil + then make sure distributor grounds good to the engine.

[Tom R.]

Re: L71 rebuilt engine won't start - follow up

I am not using the TI amp and have disconnected it's harness completely for now. The pink wire in that harness supposedly going to the ignition did not have any voltage. I found a wire near it with a simple wire spade on it and it showed 12 v with the key on. I can only say it has been added at some time and haven't been able to trace it back as of yet. But it did give me power and I connected it with the coil. The feed from the temporary replacement points distributor is connected to the negative side of the coil. Will inserting a ballast resistor prior to the positive side of the coil help me for what I'm trying to achieve?

As for getting to TDC from earlier - I bumped the engine over until compression is felt with a finger over the #1 plug hole (front left hole). Compression is definite and will move your finger off the hole. At that point, the harmonic balancer mark is usually near if not somewhere on the timing tab. I finished by turning the engine by hand via the balancer bolt until the mark is aligned on the tab at either 0, 5, 8, or 10. As I said, I tried all of them during a four hour period. When I picked up the engine the rebuilder said he had it primed for start with the valves adjusted and the initial timing was already set at 8 degrees. I should have been able to drop in the distributor and at least start it but low voltage coming from somewhere caused no or little spark. That's why the replacement distributor at this point. So now, with spark, I can't get it anywhere close to timed enough to run.

[Timothy B.]

Re: L71 rebuilt engine won't start - follow up

Tom,

The ballasr resistor will reduce voltage to the coil when it gets hot to keep the points from burning. I think on your 69 there is no ballast resistor but a resistor wire with white wrap that runs to coil+ but if the car originally had TI the resistance wires are in the TI harness. Installing the distributor by your method should work and be on #1 compression stroke.

Remove the distributor and turn the bottom gear 180* and re-install by your procedure. If the camshaft has been replaced with other than GM sometimes the bottom gear needs to be turned to allow proper timing.

[Thomas H.]

Re: L71 rebuilt engine won't start - follow up

I am not using the TI amp and have disconnected it's harness completely for now. The pink wire in that harness supposedly going to the ignition did not have any voltage. I found a wire near it with a simple wire spade on it and it showed 12 v with the key on. I can only say it has been added at some time and haven't been able to trace it back as of yet. But it did give me power and I connected it with the coil.

Tom,

Does the wire you are using provide 12 volts while cranking? Some circuits are shut down while cranking and only provide voltage when the key is in the on position.

You don't need a ballast resistor in line to get it going. The resistor is there to limit the current to the coil after the car is started. It is bypassed during cranking. After the car starts, the resistor is switched in to limit the current (dropping the voltage) to the coil making the coil run cooler thus extending its life. Running the coil on fulltime 12 volts will be fine to accomplish what you want to do in the short term.

Keep us posted on your progress.

Tom

[Duke W.]

Re: L71 rebuilt engine won't start - follow up

Disconnect the alternator and hot wire the coil to the battery with the single point distributor. This is simple to rig up and will prevent the coil from overheating. Running voltage should be about 11-12 versus 8-9 that the TI coil normally sees, and the battery should have enough energy to keep the engine running for at least 30 minutes. Monitor system voltage, and if it drops below 10, hook up a 6-10 amp battery charger, which will carry the load.

This will allow you to start the engine and accomplish the initial break-in.

If this simple setup doesn't work, try another coil. You can buy a generic 12v coil at auto parts stores for about 10 bucks. It sounds like you are installing the dist. properly - target about 10 initial.

My best guess is that, assuming the coil is okay, you have some problem in the wiring. Look at the chassis wiring schematic and start checking for continuity/resistance and proper configuration.

Duke

[Jerry M.]

Re: L71 rebuilt engine won't start - follow up

Tom
I can feel your fustration with this so I'll share a bizarre incident I came across while firing my '66 big block up the first time after its rebuild.
I installed a regular point type distributer to fire it up since the TI harness and amp was in the body, sitting across the garage from the chasis/engine. I bought a "rebuilt" distributer spec'd for a '66 427/425 (albeit with points) from our local NAPA store.
The motor fired up pretty quick but wouldn't run worth a darn...no power, backfiring, etc. I called my engine builder (locally well known big block chevy specialist) who doesn't live far away and long story short...he looked close at the distributer and found it only had six lobes on the cam.
You can imagine then how this thing sounded while trying to run.
It sounds like you're running out of ideas so I thought I'd share this "it could only happen to me" tale with you.
When it was all said and done, we were still scratching our heads trying to figure where the heck this bogus distributer came from (early, pre HEI 4.3L maybe).
Good luck,
Jerry

[Tom R.]

Re: L71 rebuilt engine won't start - follow up

That's a new one I'll check that this afternoon prior to my next attempt. I,too, stopped by the rebuilder's shop yesterday afternoon and laid everything out there to him I've tried. He could feel my pain but couldn't refrain from laughing. Said it was the first one he'd rebuilt that didn't fire right up. That didn't help either. Anyway, he offered to come over after work today and get it started for me. I'm simply gonna hand him the key when he gets out of his car. Seriously, I will check the rebuilt distributor as well as get a cheap coil and wire it directly to the battery. Thanks to everyone in this support/therapy group. Hopefully, I can post later this evening that it's up and running.

[Tom R.]

Re: L71 rebuilt engine won't start - follow up

My engine rebuilder (30+ years experience) came over this afternoon to help. After an hour or so, even he was stumped. We checked everything and finally agreed to remove carbs and intake to rule out something foreign left in the block/heads, etc. Yeah, we were literally at that point. The engine was basically acting as if it were starved for fuel and/or had a vacuum leak even though neither was the case. I have tried to react to everyone's advice over the past few weeks and will have to give the honors to Duke. It was something he said in his last "assuming the coil is good". Well, I had been sort of - and tonight even though it showed 12 volts across while cranking I assumed that meant it was okay. Well, turns out it wasn't. On a whim. I stopped this afternoon and spent $20 bucks for a replacement just because nothing else was solving my problems. Even my engine rebuilder ruled that out from the start tonight but before we started removing carbs, etc. I said what the heck it'll only take 5 minutes. Yeah, you know the rest - she fired right up. Again, thanks for everyone's input and you can look for me in St. Charles this weekend. I'll be the one with a smile on my face.

[Duke W.]

Re: L71 rebuilt engine won't start - follow up

Measure the primary and secondary resistance. What is it compared to specs in the CSM? It's possible a winding is partially shorted or even open. That may tell the story.

Open or out of spec resistance could lead to weak spark energy - not enough to light the fire.

Duke

[Jack H.]

Re: L71 rebuilt engine won't start - follow up

Measuring primary/secondary resistance is a necessary but not a sufficient test.... I've seen coils where both the windings are intact, but the magnetic core is shot and therefore little/no magnetic coupling of energy from side to side.

The only really good way to test a coil is to input a pulse on the primary and measure the resultant wavefrom from the secondary. Of course the coil needs to be loaded and repetitive testing to develop internal heating increases the validity of the test.

[Duke W.]

Re: L71 rebuilt engine won't start - follow up

True, but in this case I am wondering if a simple static resistance check will indicate a problem.

Coil problems are probably more common than many may believe given the age the the cars and the suspect quality of some reproduction coils.

It's a good idea to have a known good spare around. Any junk yard 12v GM coil that tests out okay on a running engine is satisfactory for this purpose, and generic 12v replacement coils are inexpensive.

Duke