A couple of recent post on this forum got me to thinking, the subjects were, timming marks on flywheel & timming marks.
Lots of times the timing marks aren't easily seen for different reasons & this can be a problem when your trying to find top dead center on the compression stroke, in order to install the distributor or to check the valve gap on a specific cylinder. Over the years I have found some information that was especialy usefull in solving this little riddle, I don't remember exactly where I found it I think in an old Allis Chalmers tractor manual. The procedure was called companion cylinder method of adjusting valves. I have used this method on 4 cyl. 6 cvl & V8 engines, and once you get it down its about as useful a piece of knowledge as I ever acquired.
Ok in order to explain i'll start with the general knowledge about cranks,cylinders, and valve timming, The spot marked on your flywheel for 216, 235, 261 chevrolet engines or on the harmonic balancer on , 230, 250, & 292 chevrolet engines is a reference point so that you can tell when the engines #1 cyl is at top dead center, however it doesn't tell you if your piston is up to fire or up at the top of the exhaust stroke. A good way to tell this, and is what you have to use for the companion cyl method, Is to turn the engine in the direction it normaly rotates and watch the valve train work. Watching the valves on #6 cyl when the exhaust valve closes and the intake starts to open, stop right there and you will know that #6 cyl is at top dead center on the end of the exhaust stroke, fixing to go down on the intake stroke, and #1 cyl is up on Top dead center to fire ,or start the power stroke.
#1 and #6 are companion cylinders, thus the name companion cylinder method. Also the other pairs of companion cylinders are (#2 and #5), and (#3 and #4). If you look at your distributor plug wires, companion cylinders are always wired straight across from one another on your distributor cap, and this is a good way for you to distinguish them. If you ever have your 6 cylinder head off and notice (#1 and #6) pistons travel up and down in their respective cylinders at the same time, You will also notice that numbers (2 and 5) also do this, as well as numbers (3 and 4)also. Each cylinder has a companion that is at top dead center at the same time it is. By watching the valve train on any one cylinder you can tell when that cylinders companion is at top dead center and up to fire.
If you use this method and get proficent with it, it will help you adjust valves ,set your distributor right,make it much easier to wire your plug wires in their correct order,and just give you a better understanding of valve timing events and the way your engine works.
In review valve cover off, rotate engine in direction of normal rotation, watch valves on #6, when exhaust closes and intake starts opening, stop there and adjust valves on #1 cylinder, rotate on watch #2 and adjust # 5, rotate on watch #4 and adjust #3, your half way through, watch #1 adjust #6, Watch #5 adjust #2, last watch #3 adjust #4.
Thanks for letting me bore you with this little explination of companion cylinders and how knowledge of them can help you .......Ronnie
