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Top dead center

C

cjn

Member
How do you know you are at Top dead center when timing a tractor without taking the engine apart? I can find DC on the flywheel, but can't tell where the number 1 cylinder is on the stroke.
 
There are 2 times a piston is at TDC. One time on compression and one time on exhaust so with the mark lined up you have a 50/50 chance of being right unless you have some help and you do the thumb trick as in hold your thumb on the plug hole while some one turns it over or you pull the valve cover and make sure both valves are closed either will be on the compression stroke
 
But you can hold your thumb flat over the plug hole, pretty much sealing it off, then when the upward motion of the piston pushes air out the plug hole farting at you, you know you're coming to TDC on compression.
 
Also if you would happen to get it 180 out as in on the exhaust stroke it is an easy swap of plug wires across the cap to get it right.
 
Top Dead Center is when the connecting rod throw
of the crankshaft is at the top of the circle of it's travel,
and has stopped the forward travel of the piston in
the cylinder and is commencing to pull the piston
back down.
Can be determined with a dial indicator touching the
top of the piston.

Mark the flywheel when the piston
is within .050" of top of travel, then mark the flywheel
again when the dial indicator has topped out and went
back .050" . TDC will be halfway between the two marks.


Many dial indicators can be fitted with an extension to the
tip that will reach in through the spark plug hole.
 
Different methods between gas or diesel.. and engines..
If its diesel, about 80% of the injection pumps have a side cover or plug that can be removed to tell you when #1 is coming up on compression stroke.
Beats the heck outta taking off the valve cover.
 
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