The Stovebolt Site Forums The Shop Area Engine Shop Finding TDC and flywheel installation ?

(216 engine) I need to find TDC to install the distributor. The manual says the flywheel can only be installed one way. When I rotate the engine with my finger on the #1 spark plug hole as it comes to the top of the compression stroke (no longer pushing air out spark plug) it does not appear I'm close to the triangle on the flywheel (is that the TDC mark?). I've read of a way to find TDC by installing a tube filled with oil on the #1 spark plug hole and plan to do that.

I guess my questions are:

1. Could I have installed the flywheel wrong even though all the pins and bolts lined up?
2. Is the triangle TDC?
3. What other markings are on the flywheel?
4. Is there an easier way to find TDC other than the oil tube method?

The very simple way to find TDC, as well as figuring out which stroke the piston is on, involves watching the valve rocker arms on #6 cylinder. "TDC" simply means "top dead center", and that happens twice in a 4-stroke cycle, once at the top of the compression stroke when the spark plug needs to fire, and again one turn of the crankshaft later, when the exhaust stroke is finishing up. If you time the distributor to TDC on the exhaust stroke, even though the ball and pointer are aligned, the engine won't run.

Take all the spark plugs out so you're not fighting compression, and turn the engine clockwise from the front by turning the fan blades. Watch the last two valve springs back by the firewall. You'll see the last valve start to open (compressing the spring), then it will begin closing again. Just as that spring reaches its full-closed position, the second spring from the back will begin to compress. At this point, #6 cylinder has just finished its exhaust stroke. The #1 cylinder will be at the top of the compression stroke, ready to fire the spark plug. Install the distributor with the rotor pointing toward the #1 plug wire and turn the distributor housing clockwise until the points are closed, then rotate the housing CCW until the points just barely open, and lock the dizzy down at that point. The spark timing will be set close enough to start the engine. Even if the flywheel happens to be installed wrong, this method works. The only possible way to have problems is if the camshaft timing is incorrect, with the timing marks for the crank and cam gears out of alignment. Once it's warmed up, minor spark timing adjustments can be made to get it running smoothly. No oil, no mess, and it works every time. Just be sure the tang at the bottom of the distributor shaft is fully seated in the oil pump drive as you install the dizzy.
Jerry

Edit: There is also a round mark on the flywheel, sometimes called a "ball" or a 'BB" which is actually the ignition timing mark. With the crankshaft turning clockwise, the ball will move past the pointer slightly before the triangle appears. The triangle is actually used for setting valve clearance, not for ignition timing. Either one should be sufficient for getting the engine running, but if you're setting the timing with a strobe light, use the ball,not the triangle as a reference point.
Jerry

Edit #2: Be sure you're looking into the hole in the bellhousing on the passenger's side above the starter. The one on the driver's side does not have a pointer in it, and no timing marks will align with that hole!
Jerry

Thanks Jerry. So do I understand there is no mark for #1 cyl TDC? And, do you (or anyone) know if the flywheel can be installed in more than one position?
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Because of the way the crankshaft is made, the #1 and #6 pistons reach TDC at the same time. Ditto for #2 and #5, and #3 and #4. There is no way to determine which cylinder is at TDC on the compression stroke without looking at the valve action. All engines with an even number of cylinders except a few oddball V-6's share this situation. Two pistons will reach the top of their respective strokes AT THE SAME TIME. The only way to pick out which one is on the compression stroke and ready to fire the spark plug is to understand how the camshaft and the valves operate.

The triangle on the flywheel indicates that both #1 and #6 pistons are at the top of the stroke. I haven't looked at the crankshaft/flywheel mounting procedure in awhile, so I can't be sure if the flywheel could be installed incorrectly. If so, then one of the other cylinder pairs would align themselves with the timing marks. I think that is VERY unlikely, as all automotive engineers try to make their engines as idiot-proof as possible. If your timing marks at the flywheel are not aligning with TDC according to the valve action, it's very likely that the camshaft is installed incorrectly.
Jerry

Jerry,

Success! Thank you for you help. I tried just watching the valve springs, but doing it by myself I couldn't turn the engine and keep a close enough eye on the springs. I ended up using a tube filled with oil pic
Once I found TDC I compared it to the flywheel and I was sitting right on the U/C mark. I also marked the front pulley and timing chain cover to get an idea of where the other marks (triangle and BB) were. You can see photos here

Your posts really helped me to understand what I was doing. Thank you.

I don't understand what you are doing with the tube of oil or why it's needed. Care to explain that rig?

Looks to me like it would be a whole lot easier to pull a valve cover than rig that set-up.

It's a "manometer" rig, just using oil instead or water. It shows when the air stops flowing out of the cylinder, and the piston starts back down by watching the changing level of the liquid. It's a little bit of overkill for finding TDC. I've used something similar on an oldtime Sun distributor tester for setting early Ford V-8 "Vacu-matic" distributors that had a vacuum advance that responded to venturi vacuum in inches of water, not manifold vacuum.
Jerry

Cletis,
What Jerry said...but while overkill for someone that's done this a bunch, it's an easier visual for a newb. I just wasn't able to determine exactly when a valve stopped moving. With the tube of oil it was very obvious.

Here is a link with some more information about the manometer method.

For a 216, one degree of rotation from TDC produces about 0.0003" of piston movement and about 0.10" of oil movement in a 3/16" ID tube. Two degrees of rotation from TDC will result in about 0.40" of oil height change. Could be as accurate as the positive stop method for finding TDC. The manometer method could be good for an engine (like one of mine) where a bolt through a spark plug doesn't touch the piston.

Hoyt

With the TDC mark lined up with the pointer both cylinder one and cylinder six will be at top dead center. One of them will have both valves closed and the other won't. This is obvious by looking at the rocker arms. And the mark lined with the pointer is as accurate as you need to be.

You don't need a bolt in the spark plug hole to determine this. You don't need a manometer hooked up. This is complicating a simple procedure and probably confusing people in the process.

X 2 on what Cletis said.

If you don't like looking at the valves, you can wad up a piece of paper and wedge it in the number 1 spark plug hole. When the number 1 piston begins it's compression stroke, the paper will shoot out like a spitball in Sister Mary's 4th grade class. continue turning the motor by hand untill the mark on the flywheel is lined up with the pointer.