November 27, 2005 - November 30, 2005
Backwards Distributor Riddle
An interesting ignition problem surfaced While attempting to get the engine running last year. An experienced VW mechanic would have known exactly what was wrong after a visual inspection of the timing, but for me this was a big riddle.
It seemed like the ignition was running backwards!
I have attempted to explain this clearly, but I admit I was confused for most of the process described below.
All the VW engine books say the front right cylinder (closest to the frontseat passenger) is #1...
...and the front left cylinder (closest to the driver) is #3.
When timed correctly, the rotor points to this notch on the body of the distributor when piston #1 is at top dead center. The firing order is 1-4-3-2. Even says it on the generator pedestal!
On MY engine, piston #3 was at TDC when the rotor pointed to the notch. When the rotor was 180 degrees AWAY from the notch, piston #1 was at TDC. The distributor was wired accordingly, and the engine would run. Being new to VW engines and lacking confidence, I had to first convince myself I knew which cylinder was which. I wasn't sure if the piston numbering diagrams were from the top or the bottom- they actually are from the top of course, but it would mean my engine was timed correctly if the diagrams were from the bottom.
Once I was convinced of the piston numbering, I could focus on other possibilities. I thought maybe the crank was installed 180 degrees out. One book says to hold rods #1 and #2 while lowering the assmebled crank into the left case half. Maybe the person who put this engine together held #3 and #4? Nope- would not matter to the distributor, and is not possible anyway because with the #1 and #2 rods going through the #3 and #4 holes the crank would not line up with its bearings... or anything else for that matter.
Ok, then how about the distributor drive gear? This one is a little funny- there is no trilogy of dots to line up like on the camshaft and its drive gear. So how does one know if the distributor drive gear is lined up? It actually does not matter how the drive gear lines up (it is keyed on the crankshaft anyway), but it does matter how the other end of the distributor driveshaft is oriented...
The other end of the distributor driveshaft has an offset slot this tab on the bottom of the distributor fits into. This way it is impossible to install the distributor backwards. On type I engines the slot in the distributor drive shaft must be installed perpendicular to the split in the case halves with piston #1 at TDC. (Note: Other engines have a different angle.) The larger portion of the offset faces the flywheel while the smaller portion faces the rear of the engine. But what if the engine builder put the distributor driveshaft in with the offset backwards?
Then it is impossible to install the distributor correctly! Right now #3 should be at TDC, but this is where MY #1 is at TDC. The distributor can only be installed backwards, which means the wires must be ran to the plugs backwards. So the firing order is now 3-2-1-4. Is this OK? It ran so it must be, right?
No, maybe not! It has been claimed in earlier (non-doghouse) engines, not all the cylinders fire evenly spaced from the others. It is said that #3 is a little behind so it runs cooler to make up for getting hot air out of the oil cooler. Some distributors supposedly have this timing feature and others don't. I'm not too sure about mine although it does have a 009 distributor and is a 1971 doghouse engine. So if I had to guess I would say my engine does not have or need the #3 retard feature. But if it did, with my engine's incorrect timing, #1 would be needlessly losing power while #3 runs even hotter than normal. Who knows what I will find around #3- cracks, greatly worn cylinder, or nothing unusual.
So what exactly went wrong? One of two possiblities.
1) The engine builder knew which cylinder was which but installed the driveshaft with the larger portion of the offset to the rear of the engine. He must have realized it too late and not having a distributor drive shaft puller and not wanting to split the case just wired it up backwards so it would run and sold it to a dumb college kid (me at the time.) Or...
2) The engine builder did NOT know which cylinder is which, had them backwards in fact, and had #3 at TDC when he installed the distributor driveshaft correctly. He did not realize he was wiring the plugs backwards as a result of having the cylinders numbered backwards in his mind. THEN he sold the car to a dumb college kid.
How can this be fixed? Well, dumb college kids eventually graduate and learn more about the world, but that is a different story... As for the distributor, if there is a distributor drive shaft puller available (about $20 in November, 2005 dollars), the shaft could be removed, turned around 180 degrees, and then reinstalled. I probably won't do this because my intentions are to take the engine apart anyway.
As mentioned earlier, the experienced VW mechanic would likely go right to this conclusion. But for me, it was a challenge. I am in one way glad the engine had this problem because to find it I had to first learn a great deal about how the aircooled VW engine is built and operates. Granted, it takes a lot of time to learn new things but to me it is leisure time. Part of the benefit of a wrecked-to-reliable transformation is knowing much more about the vehicle. It is the added benefit of being able to diagnose almost any problem that arises whether it is in the garage or along the road somewhere.