OK, I now know that drinking and setting up your ignition doesn't mix. I had put the dizzy in 180 degrees out. (I felt like I was back in high school) With it 180 out, it ran and I drove it around the block. It was what you would expect. Low power, burping and missing. The problem is that now that I set it right, she won't start. All I get is an occasional back fire. Any ideas?
I got it running last night. Now it runs perfectly. You are right about the 180 out, it was right the first time. It ran so poorly due to noise and setup problems related the the MegaSquirt and the MSD-6a. It was a strange combination of errors. What confused me with the 180 issue was that when I had it right I also had swapped the coil and #7 plug wires on the cap. Everything works if you let it.
On my car, I can see the cam position on #4 through the oil fill cap and know when I'm 180 out. YMMV but it beats trying to feel a puff of air through a spark plug hole! Ken
Now now Ken. Nothing ever really beats trying to feel a puff of air, lol. And drinking and fixing cars is quite fun. Always interesting the next morning to see what you put together backwards. My wifes Dad used to build model railroad stuff. He would sit up sometimes late at night drinking wine, glueing plastic and wood buildings together and spraying paint with an airbrush. The next day would be spent ripping it all apart and repainting it.
Oh, I've been known to have a beer or two when working on my car, at least in the summer. The first time I timed my ignition I was 180 degrees out and couldn't figure it out until someone clued me in on looking at the cam through the oil fill hole. My compression is 168-170 across the board but I never could feel the puff...too much beer? Ken
Or not enough??? The flexhose with the airchuck fitting for the compression tester allows for much more dynamic puffs. Course once you have that screwed in, you could attach the airhose and roll the motor forward until it seals up, then you know your on the comp. stroke. Just move up to TDC and your there.
I found it by putting a cork in the plug hole and turning the motor till it popped out. As for putting air into the plug hole, don't both valves close between the exhaust and intake TDC change over?
Yes, thats the point. Once you stop losing air you know it has to have both valves closed. Roll it up to TDC and your there.
Won't it stop losing air at both TDC points? Once at the top of the compression stroke and once between the exhaust and intake stroke. At both points aren't both valves closed?
Compression stroke all valves are closed; hence the puff through the spark plug hole. Exhaust stroke has the exhaust valves open. Only on the compression stroke is the pistion moving towards the valves with all the valves closed. Ken
OK I'm missing something here. Aren't both valves closed at the TDC changeover between the end of the exhaust stroke and the beginning of the intake stroke? And doesn't this happen 180 out from TDC of the power stroke?
Depends on overlap. Hot cams have overlap in the timing so it's not an all or nothing thing. I'm not sure where that occurs, but to feel the "puff" you need the piston moving to the valves with all of them closed, and that only happens at the end of the compression stroke. The next is the power stroke so that's TDC for setting #1 spark plug to fire, not counting degrees of advance you dial in. It's really quite logical: Intake stroke: intake valves open, exhaust closed. Compression: all valves closed (puff of air in spark plug hole). Power: all valves closed but the piston is moving away from the valves. Exhaust: intake valves closed, exhaust open. Ken
I think your forgetting that the engine has to rotate two full revolutions, 720 degrees, incorporating four "cycles" of the piston going up or down, to fire one time. I been accused of being long winded before, so bear with me. Starting at 0 degrees TDC, (which is "after" the spark fires off combustion, by the way) the "power stroke", the piston is pushed down by the expanding gasses, all valves are closed. At a point past half way down, around 30 to 40 degrees BBDC, the exhaust begins to open. At the bottom, BDC, 180 degrees of rotation, the exhaust is still opening, and the piston begins to travel back up, beginning the "exhaust stroke". At around the half way point, around 80 to 100 degrees BTDC, the exhaust is fully open, and in most engines will remain open until the piston passes over TDC, at about 20 to 30 degrees ATDC. Somewhere past the half way point going up on the exhaust stroke, at about 20 to 30 degrees BTDC, the intake will begin to open, now both valves are open, this is the "valve overlap" phase. Both valves in most older engines will remain open through the TDC event. As the piston passes over TDC, one complete revolution of the crankshaft, 360 degrees of rotation, has occured, the exhaust is now closed or will be shortly. This is the "intake stroke. The intake will be fully open somewhere around the half way point of the intake stroke, again, around 80 to 100 degrees ATDC. The intake valve will remain open as the piston passes through BDC, now 540 degrees of rotation, and remain open until around 30 to 40 degrees ABDC. This is now the compression stroke. In a properly tuned 308, at anything over 5000 rpm the spark should fire at 34 degrees BTDC on the compression stroke. This is because during the time it takes the crankshaft to rotate 34 degrees to TDC, about .007 of a second at 5000 rpm, combustion pressure will not have increased appreciably. Fatter cams will open the valves sooner, close them later, and in many cases open them farther and hold them fully open over a longer period. But more radical cams also have dramatic effects on idle quality and low speed emissions that gets worse the more radical they get. On later model cars they excessivly narrow the overlap period, and in many cases actually close the exhaust valve 10 to almost 20 degrees BTDC, like on the injected and QV cars for example. My P6 cams, on the other hand, can open the intake at around 50 degrees BTDC, and keep the exhaust open until 40-50 degrees after ATDC, depending on how they are set up. So you can see that valve overlap can be extended from as little as 10 to 20 degrees, to 100 degrees or more. But in any case, any engine, no matter how mild or radical will still have both valves closed at TDC on the compression/power stroke, and at the very least, the intake will be open at TDC on the exhaust/intake stroke. If you apply air pressure to the cylinder, the only time air will not leak out appreciably is when both valves are closed, which only occurs in the TDC area between the compression and power stroke. Anywhere else has one, or both valves open.
