MGB - Ignition Complete

My last couple of posts have spanned 3 weeks, and, honestly, most of the work has as well. Today's post ends with a running car, and covers the final step in the ignition journey.

 

Best Laid Plans

I thought my plan was so simple. I would just pull out a box of bolt-in ignition parts and I would go from a running-crummy car to a magical sled. As you have witnessed from the last couple of posts, it was not that simple. First, the battery was dead, then the fuel pump was bad. Now, we are finally ready to set the timing, but there doesn't appear to be any spark coming from this new ignition. Why?

Lucas, Lord of Darkness

First, that's not my joke; I borrowed it from Hal. Thanks, Hal. Years later, its still funny, and in so many cases, its still true.

Lucas CEI ignition wiring diagram

I figured that the red and black wires for the ignition signal in the new distributor could just re-use the red and black wires that had been feeding the old distributor. That was my mistake, because I did not recognize this was not your standard distributor. No... this was a Lucas CEI ignition system. While I imagine these were great in their day, this set up was a little more complicated. The 2-wire signal going to/from the distributor does not go directly to the coil. It routes through an amplifier box. This amplifier box appears to only work with the Lucas stuff, though. I believe that either the replacement hi-power coil, the new distributor or both are not compatible with the amplifier box.

The amplifier does not make things much more complicated: it only adds 2 wires to the coil, but the wiring around the coil is already a little confusing. Add in some extras and some grease shmears and trying to figure out what wire is for what starts to get more difficult, especially when the wires are not in the standard diagram. The image above is correct, but it is not in the standard "advance autowire" wiring diagrams, nor can I find references to the Lucas CEI in the MGB shop manual that I have. Still, this research did tell me that there is no ballast in the circuit from the coil to the distributor. There is a ballast between the coil and the fusebox (and that remained), but I figured I should be able to direct-wire the red/black wires to the +/- on the coil directly. The picture below should help show what a "ballast" coil set up looks like. See that "distributor resistor" in the drawing below? It is not in the drawing above so I don't have that. So, we start over. Kinda.

 

Final Install

standard 1978 ignition wiring diagram

I started by removing the distributor again. I had moved the 2-pin plug from the Lucas distributor onto the AccuSpark so I undid those solder joints and soldered on 2 1-foot lengths of 16ga wire (black and red for negative and positive, respectively). I heat-shrink'd the solder points. To the ends of these wires, I added female wire disconnects and heat-shrink'd those as well.

Next, I disconnected the wires going to and from the amplifier box and then removed the box itself. I re-installed the coil and the 2 things that shared the mount-points with 2 shorter bolts. Then, I slid the distributor back in, and re-set the mounting bolt to hold it firm. I had found TDC earlier, as noted in my previous post, so I oriented the distributor visually into the same place (took a picture before removing). In theory, everything should be fairly well set, at least well enough to start, albeit roughly. I optimistically pulled out my timing light just in case.

On an aside, the MGB battery is behind the passenger seat. This makes use of a timing light challenging. To remedy, I sat an old battery on the floor by the front bumper on the passenger side and clipped my positive and negative leads for the timing light onto it. 

It's Alive!

tidied up

I double-checked my under-hood connections, turned off the KBOO and then returned to the driver seat. I turned the key to run and heard the click-then-hum of the fuel pump as well as a click from the engine compartment. Thinking that was the coil leaping to life, I turned the key to start and Oliver started immediately. I mean immediately. No ba-ba-ba beforehand, no choke needed. He just started, and then dropped into a lope-y idle.

Setting Timing

Thrilled, I clipped my timing light sensor on spark lead #1 and pointed it at the main pulley. It flashed on the timing mark, indicating I was around 10* before top dead center (BTDC), which was in the ballpark (suggested 6-14 degrees advanced from TDC by AccuSpark). I tried rotating the distributor housing a little bit to advance or retard the timing, and found that Oliver was most content around 12* BTDC. My light is a cheapy, and does not have a knob to check full advance. So, instead, I used my ears, revving the engine up and down and then revving it up and quick-pulling my foot off the pedal. This last test was when Oliver used to backfire. There was none of that now. Of course, he is not under load right now either. Undeterred, I went back up front and checked his timing again: he was still settled at 12*.

I turned off Oliver's engine and tightened down the timing adjust set bolt (5/16") so the distributor would not rotate on it's own, and his timing would be locked in. I was done. Wow. I hadn't expected that. So, I spent a few minutes cleaning up some of the wiring that I had earlier cut loose from the taped loom by encasing it in some basic wire wrap.

leads now

I included the before picture of my ignition below (blue leads) and a picture of the ignition now on the right here (red/orange leads), taken from about the same spot. If you look closely, you will notice that the newly installed distributor is oriented at least 45* anti-clockwise compared to how it was before. So, either I had moved the dizzy a little before taking that before picture or the engine was running so incredibly off it is kind of a miracle it was running at all. Perhaps the backfires on deceleration could be attributed to the timing being so far off that the dizzy could not get back to a fire-at-the-right-time state when I took my foot off the pedal.

At this point, I'm not sure it was ever firing at the right time. Based on how quickly he started, and how well he ran after I revved him a few times, I am confident the mark I used for TDC and his timing are correct. The lesson here, I think, is to give your new-to-you car a tune-up as soon after you get it home as you can. I have been given this lesson before (See Bay City Blues), but I guess I need multiple examples before I learn sometimes. Bare minimum, I will start looking at my spark plugs during oil changes so I have a regular insight into the combustion. Might be worth a quick validation of the timing when I do that.

Next?

Oliver is pretty much ready to go again. He hard-started a few days after I did the timing I mentioned above. So, I still need some carb adjustment time, and he needs to go through DEQ, of course. An oil change is overdue as well. Otherwise, he is practically ready for Summer. As am I. Just thinking about a top-down drive with Boo for a picnic at a park sounds just about perfect. I'll post on the carb tuning when I get to it.

leads before

I'm not sure what I will be working on next, but nice weather is right around the corner so returning to the paint on Zed is inevitable. Some of him sat outside all winter, so I imagine there is quite a bit of rework coming before I can think about laying paint. Meanwhile, T is due back in the Pacific NorthWest to fight forest fires somewhat soon, and he will probably want/need Nemo on his off days. So, maybe I need to get that rear end sorted. Of course, Nemo won't start now or even put a signal to the OBD2 plug, so he is going from bad to worse fast.

Regardless, there's always something to do at ShadeTree, like helping a local kid swap out his muffler. Oops, I guess I forgot to post on that. We had fun and he learned something: a fart can muffler on an otherwise stock exhaust doesn't really do anything. For a meaningful change in tone and performance, he will need to remove at least one of the other resonators. He is saving up for a cat-back; that will be fun.

Thanks, as always, for following along.