Cam timing chart

[304065]

I like to be organized so I made the following chart to help me with cam timing. Basically the operation is not more complicated than that explained in the factory manual, but I like to overcomplicate things. This chart shows what each piston is doing. But the key point, in my case, comparing the timing of Cyl1 with Cyl4 is that when Cyl1 is at the timing point (labeled OC in the chart) Cyl4 is at the firing point (labeled TC in the chart). Of course I know that the firing point is not exactly TDC but you get the idea. Green= power, Gray= exhaust, Blue= intake, Red= Compression.

[304065]

Reality check. #1 at overlap, #4 at compression. (the firing point)

[Walt Fricke]

John

I read this as #1 at TDC firing (approximately re: ignition advance) - a time when you can wiggle both rockers, because both valves are closed.

And #4 at overlap, when you can't wiggle either rocker.

Counting the left side of your chart as the point where this is true.

At the middle of the chart these roles are reversed, as they should be for these two cylinders.

So your 2d post confuses me.

Which is not hard to do.

Walt

[304065]

Walt, I wrote that during a break from my cam timing procedure. It's one of those things where all the noise over the years on this forum and others has elevated the cam timing procedure to something akin to a Shuttle Launch. When in reality, it's pretty simple-- given the 162435 firing order and that it's a six cylinder motor with crank throws spaced 120 degrees apart, the #1 and #4 pistons are always in the same position-- when one is on TDC compression, the other is on TDC overlap.

I like your memory aid better- when #1 valves both wiggle, #4's dont. I had a hell of a time running dual mitutoyo indicators as a check, because I thought that both should read the same ON THE SAME REVOLUTION OF THE CRANK. But in fact, first one reads the timing spec, then you turn the crank 360 degrees, and the other one reads the timing spec.

The cool thing about the mitutoyo digitals is that you can ZERO the one that reads the cam setting, while the other is at zero, and they WILL both read the same. This provides the check you're looking for, but it's easy to drive yourself crazy, thinking, "did I time the starboard cam 180 degrees out of phase?"

It was in the middle of one of these second (or third, or fourth)-guessing moments that I wrote the above.

OK, back to putting the heat exchangers on . . . .

[911st]

sub'd

Way cool chart.

Also kind of displays the overlap of exhaust events on a stock merged exhaust system that might contribute to exhaust reversion (back pressure).