See full version: How to Find Your Engine s Top Dead Center (TDC)
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Top dead center, sometimes referred to as TDC, is the point in which the piston in the number one cylinder position of your engine is at its highest point on the compression stroke. You may need to identify top dead center in order to install a new distributor in the correct orientation, connect spark plug wires in the correct position or any number of other automotive projects. Doing so can be easy with ordinary hand tools, but using a piston stopper tool specifically designed to help find top dead center will yield the most accurate results. more
To find your engine’s top dead center, locate the crank pulley near the bottom of the engine and use a wrench to turn the nut in the center of the pulley. Turn the pulley with the wrench until the piston in the first cylinder comes into contact with the other piston. When it stops, use a marker to mark the pulley location on the harmonic dampener, or the metal housing over the pulley. Then, use the wrench to rotate the engine the opposite way until it comes back into contact with the piston and mark the second spot on the harmonic dampener. After that, find the top dead center point between the marks by measuring the distance and dividing by 2. For tips about how to locate the top dead center without a stopper tool, keep reading! [links]
There are lots of reasons and various occasions for needing to find Top Dead Center (TDC) for your engine. TDC is the point where a piston is exactly at the top of stroke, and the crankshaft connecting rod journal is exactly straight up (in a vertical engine of course). Sometimes the need is rather casual, like getting it in the ballpark so you can install the distributor drive gear in the correct orientation or install spark plug wires in the correct position. Other times it needs to be a bit more accurate, like setting the crankshaft straight up so you can do a blow down test without the crankshaft turning. There are also times when it has to be dead on accurate, like when installing a special camshaft and getting the non-standard cam timing exactly right. To this end I will explore a few ways to find TDC, starting with the easiest (and least accurate).
Very often you have a completely assembled engine, and you can use the timing mark on the crankshaft pulley to find TDC. This however does not tell you if it is on the compression stroke or exhaust stroke, which are 360 degrees apart, or offset by one complete rotation of the crankshaft. With TDC on the compression stroke the intake and exhaust valves are both closed. With TDC on the exhaust stroke the intake and exhaust valves are both open (partially open). For this you can remove the valve cover and look at the rocker arms to see which ones are fully up (slightly loose) and which ones are partly depressed (intake and exhaust arms at the same height), one moving up while the other is moving down. A quicker way is to remove spark plugs and place your thumb over #1 spark plug port, then rotate the crankshaft (clockwise is best but not essential). During transition between exhaust and intake strokes when one or both valves are open, there will be no pressure. During approach to TDC between compression and power strokes when both valves are closed, there will be pressure that will push your thumb off of the spark plug port to allow air to escape. When air stops blowing out it is fairly near TDC on the compression stroke. This may be close enough to install a distributor or spark wires, but not close enough for setting ignition timing or doing a blow down test. You would be lucky to get within 15 degrees of TDC using this method, so this is only practical for determining when the engine is on the compression stroke (or not).
Once the piston is close to TDC you might look into the spark plug port to see the piston move. You may also poke a small screwdriver into the port to feel the height of the piston. Caution: Never take your hand off of the screwdriver when it is in the spark plug port. If you turn the crankshaft with a tool in the cylinder, motion of the piston may damage the tool or the port threads or the piston. You can turn the crankshaft back and forth a little while observing motion of the piston to get a better idea of location of TDC, trying to estimate the position where the piston stops moving. more
To find the compression ratio (CR) you divide the total swept volume with the total compressed volume. This is how you find out what these totals are: here
All of these elements must be measured with the same units. If you're doing a manual calculation, that usually means using cubic centimeters (cc). [links]
Swept volume = chamber volume + piston volume + gasket volume + clearance volume + cylinder volume here
How to use: simply fill in all the boxes below with the requested figures and click on "Calculate CR" to find your engine's compression ratio.
We're looking at the first of these ways here. This technique is suited to someone who is in the middle of putting an engine together and has the right tools, or someone whose engine is already in pieces. more
L.S,
What a lot - most very complicated possibilities - to find the TDC of a piston in an engine?
Just look at the marks on the flywheel
Regards
Alfons
2. Fuel Pump Method
There is a cut marking on both fuel pump body and plunger of the fuel pump. when these marking matches ; fuel injection takes place. At this point, piston ignition starts . This will be 4-6 degree before TDC and the inlet and exhaust valves are closed. more
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Thanks for reading.. complicated but in some extend it is useful. Wt will you do if the markings are not clear. here