Finding Top Dead Center
The ignition timing in my car has thus far been set to "seems to run" standard by ear. I've come to the conclusion that perhaps I should actually measure it before next summer. But, as always, there's a catch. The problem is the top dead center mark in the damper. I don't really trust that it is correct and even if it is, the water pump prevents seeing it at TDC.
Luckily I found an easy way to find the TDC without taking the heads off. I ordered a piston stop tool by Comp Cams from Amazon. It is quite easy to build a similar tool from an old spark plug but it is cheap so I decided to order one. Package arrived in about a week so I got to work.
To use the tool, I first needed a marker to the engine to use as reference. The power steering pump bracket was at a convenient place close to the damper so I decided to use it. I loosened one of its bolts, bended a small wire and placed it under the bolt.
Next I replaced the number one spark plug with the piston stop and very carefully turned the engine to clockwise direction by hand until the piston contacted with the tool. I added a small drop of paint to the damper where the marker was pointing. Next I turned the engine to counterclockwise until contact happened again and another small drop of paint was added. The top dead center is in the middle of the points. For me they were about 1,5 cm away from each other so I painted a longer line between the points. I bended the wire a bit so it was pointing at the line.
Finally I returned the plug to the first cylinder and removed all other tools from the engine bay so it was safe to start up.
Setting Ignition Timing
Another tool that I needed was the timing lamp. I went to Motonet where they had three different models:
- A really basic model that had no settings at all. It would just flash the light when the spark plug fired.
- Second, a bit more expensive one where you could set the wanted advance between 0 and 60 degrees.
- Third one was way more expensive but it had a lot of features: adjustable advance, a tachometer, volmeter and who knows what else.
To use the cheapest one, I would need to have the degrees marked to the damper itself. I could buy a ready made sticker or just count and draw them myself (damper diameter 8 inches * PI / 360 = 1,77mm per degree) but save some hassle, I bought the lamp with the adjustable advance. With that, I could just turn the knob until TDC marking aligned with the pointer and then read the advance from the lamp.
I began by measuring the initial timing. I removed and plugged the distributor vacuum hose and started the car. Without the vacuum advance the engine was idling (according its own tach) at only 400rpm so I tuned the carb a bit until it rose to 500rpm. When the engine had warmed up, I checked the timing and got about 38 degrees! Phew, that's what the total timing should be, not idle!
I turned the engine off to call a few friends and surf the web a bit. I thought I had done something wrong with my markings or something. After some investigation I came to the conclusion that it is possible for the engine to run with that much timing so it was time to correct it. I loosened the distributor, marked its initial position and started the car again.
I let the car settle to normal idle, measured the timing and got the same 38 degrees. I turned the distributor to clockwise until the advance showed 8 degrees. I was surprised that I only needed to turn it a few centimeters to get it correct. Engine also sounded better now.
Finally I also measured the total timing. I reconnected the distributor vacuum hose and asked my wife to help. She worked the gas pedal and kept the engine at 2000 rpm for me. There the advance was 30 degrees. What I read from the web, that should be OK.
Perhaps this was the reason why my engine started to get hot at high rpm on the highway? We'll see when driving season starts soon!
