While photographing interesting sand dunes, a dastardly enemy has pinched your distributor cap and left you to die in the desert. But you have a good tool kit.
Is it possible to hook the ignition coil directly to one spark plug, extract the other plugs and limp home on one cylinder? Would you absolutely have to have a HT lead, or can you cannibalise other wires from your vehicle? Do the extra sparks mess you up? (I’m thinking you might light the mix at the end of the intake stroke.) Is there a way round this (e.g. shave a lobe off the cam driving the points.)
Assume an old 4 x 4 held together with wingnuts. 4 cylinder engine, carb, coil, points, low gear ratio and not a semiconductor or a power-assisted anything to be found.
Any other thoughts about the situation would be appreciated! (It just crossed my mind that you should take the hood/bonnet off to prevent fuel-air mix from the other cylinders building up under there and making your day even worse…)
Firstly. What’s a distributor? Joking, but do they really still have those?
I don’t think it would work at all - the distributor controls the spark timing, doesn’t it? It’s bad enough when the timing is just a little bit off and you’re firing on all 4 - how could it ever work on one, with no timing management at all?
If you bypassed the cap and rotor on an inline four, one cylinder would fire at top dead center and bottom dead center on each stroke. The TDC sparks wouln’t matter; a lot of twin cylinder engines do the same thing. The BDC at the start of the exhaust stroke shouldn’t matter either. BDC at the end of the intake stroke might fire though.
The biggest problem would be having one cylinder provide enough power to overcome the resistance of the other three cylinders and still have enough left over to move the truck. At the very least, I’d remove the unused spark plugs to drop compression in those cylinders and expect to do an oil change as soon as I got home.
It’s the cap that’s missing, the plastic top with a HT lead in from the coil and HT leads out to the plugs. Used to be a standard method of disabling a vehicle…
Spark timing is governed by the opening and closing of the points, which are mechanically coupled to the crankshaft via a multi-lobed cam, no problem there.
And you’re right, the single coil distributor system has largely been supplanted by small coils for each plug or pair of plugs, and the points by transistor switches coupled to a “crankshaft position sensor”… All very reliable, but less interesting…
Still might not work though - because when the nuns did this on The Sound Of Music, they took the cap and the HT leads. I’m not sure what else could be used in their stead.
Extracting the other plugs is in the OP! This is a life-or-death jury rig, the vehicle can go to scrap afterwards…
I have driven a VW bus running on two cylinders after the rocker arm dropped off closing half the valves. It handled it, just, with all plugs left in and a dingy on tow! So I was thinking a 4 wheel drive in LOW ratio might be okay on one cylinder if you have any semblance of a road to drive on.
Your better bet might be to rig the starter to propel the car as far as the battery will take you. You could remove all the plugs in order to reduce the compression resistance. Some manual cars didn’t need rigging. You could ride the starter with the car in gear and get 'er up to 15 miles an hour no problem.
Otherwise I don’t think connecting one plug directly to the coil will get you enough “performance” to move the car anywhere for any length of time. You need the rotor cap for not only for distributing a spark but also to get it there at the proper time. I think just firing sparks into the cylinder at TDC and BDC will cause more problems and a really foul running engine, if it runs at all.
Best bet is to stay with the car, rip out one of the seats and set fire to it - adding anything else you can to make lots of smoke. Before you set out, you told people where you were headed and when to expect you back, didn’t you?
Macgyver might be able to rig the vehicle to run on one cylinder using a makeshift distributor cap fashioned from his own excrement, dried in the desert sun. Anyone else is going to die or wait for rescue, I think.
[Old mechanics story]So I had a guy strip the timing gears on an old Volvo right in front of our dealership. We pushed it in, and sold him new timing gears (the cam gear was plastic/resin and would wear out) a new distributor cap and wires. (cap was broken from when the gears went, and the wires were for shit)
Anyway I did the gears in almost record time, no problems. I gave it to my apprentice to put the cap rotor and wires on. Told him to test drive it when he was done and park it.
He got back from the test drive and said “Man that car is slow”
I said “It is a 75 with an automatic, air and EGR they are slow.”
He said, “No it’s really slow”
I said “Yeah they are really slow”
He said “No it’s REALLY slow.”
OK, I’ll go drive it.
Now mind you I had never seen this car run before, so I had no idea of it’s condition. It was 14 years old, and had almost 300,000 miles on it, so I had no idea what to expect.
Car started right up. Put it in gear and idled toward the parking lot exit. Seemed OK, if maybe a little sluggish.
Got out of the road and floored it. I think a little old lady in a walker could take this thing across an intersection.
Slow as in zero to sixty in dawn to dusk.
Back to the shop. I assumed that I fucked up the gear installation.
I tore the entire front of the engine down. The marks lined up.
Fuck
They must have miss marked the new gears. I fish out the old one and compare marks.
Fuck they match.
I put the entire front of the engine back.
I start tearing into the ignition and fuel system.
After about 20 minutes I notice that my apprentice had wired the ignition system backwards. Instead of 1-3-4-2 he wired it 1-2-4-3. This means that only cylinders 1 and 4 were firing on compression, 2 and 3 were firing on the exhaust stroke. :smack:
So I swapped the wires and it drove like it should have.[/OMS]
Getting back to the OP, I would be worried about the firing at BDC on the intake stroke. Now if you had a file or a battery operated grinder, and ground off two of the opposite lobes of the distributor then you could get it to just fire at TDC. With the plugs out, it just might run. Barely.
I’m fairly sure that isn’t the case, although I’m willing to be educated on this. I’d formed the impression that it’s only the opening of the points that fires the spark, by causing the coil field to collapse and creating a momentary high voltage. With the points closed, there’s no voltage in the coil’s secondary circuit.
In this example, ignition (spark) timing is determined by the moment the points open, which is adjusted by rotating the distributor body relative to the distributor shaft. The distributor cap is not a factor here, assuming everything is lined up properly.
Any metal wire will conduct the spark. Getting all the spark to the spark plug instead of to some handy grounding point is the job of the plug wire’s insulation. Using a typical electrical wire is doable, but could be challenging.
The biggest challenge, though, would be getting the engine to run on one cylinder. I don’t know for sure that it’s impossible, but there’s more to it than just having 1/4 the normal power. Without any other cylinders helping to keep the crankshaft rotating (momentum), I think it would be a just-barely proposition at best.
The original equipment spark plug wires on a Model A weren’t even wire. They were flat straps of copper that clipped to an exposed terminal of the cap, and the top of the spark plug. Picture here.
Are they still using series-wound starter motors? If so, you’ll burn out the motor in very short order (unless you went in jumps of a few feet, allowing it to cool. So I was told in USN electrical school (Anyone remember the “Deadly Shipmate” movie?)
Possibly, but you’re loading the starter motor pretty hard if the engine is under compression. If you remove all the plugs you remove most of the load and you’re just spinning the crank. Not all that hard for a starter to do with a good battery. Granted, now you’ve added the weight of the car to the starter load. Once you have the car moving you don’t need to keep the starter engaged the whole time, just enough to keep rolling so you don’t stop again. So, you could engage starter, drop it in gear and get up to speed (15 mph in low as per OP) and then coast (allow the starter to rest) then at about 2-5 mph give it another go and get er back up to 15 again. Repeat until the battery craps out.
Pulling the plugs seems to be allowed per the OP. Crank-and-repeat sounds reasonable, (also gives the battery time to recover), but I’m not sure I’d care to try it on my nickel. Anyone want to experiment? The world awaits results.
OK, I got it. You need a file or a battery operated grinder. You grind off two of the lobes of the distributor shaft that are 180 degrees apart. You don’t have to take them down much, 0.020" should be plenty.
You then run a wire from the coil to the #1 and #4 plug. You now have a 2 cylinder waste spark engine. With #2 and 3 plugs removed, you should be able to putt home.
Nah, my brother used to start his 80 something Mustang this way. He’d ride the starter till he got the thing going about 10-15 mph and then he’d release the clutch and dump it. It wouldn’t start any other way. Not sure what was going on there.
He did this many dozens of times, and for kicks he drove it around a very large parking lot just using the starter once. I bet he could have gone a few miles if he did it right.
