Farmall Model A finding TDC and starter issue

bobo641

Member
Finding top dead center piston # 1. My 1940 Model A has a sheet metal pointer attached to the flywheel cover instead of the cast pointer. My flywheel also has an arrow on it . the question is does the arrow have to be in line with the sheet metal pointer at 6"0 clock or before the pointer to be top dead center?

2nd question. My tractor was converted to a 12 volt system by impervious owner. When attempting to start the tractor it is (arcing) where the push rod slides through the support bracket. I also notice sparks underneath the saddle mount.

The starter was just repaired by a reputable repair shop in my area. no issues testing the starter on the bench. However once saddle mount installed and starter installed i had these issues.

Any help would be appreciated on these 2 questions.
 
To find real TDC on #1: Take out #1 spark plug (toward radiator). With the ignition off, and the
tractor in 4th gear on pavement/concrete or packed earth, have a friend push the tractor forward
slowly, while your thumb is in the spark plug hole. When it starts on the compression stroke, air
will push past your thumb. As soon as you feel the air, put a plastic soda straw in the plug hole.
Again move the tractor and watch the straw. (you can probably put it in neutral and turn the fan at
this point) when the straw stops moving up, you are at (or very very close to TDC. Look for the
markers at this point.
Your starter saddle switch is bad. The insulation between internal conductors, and the switch body
have failed. New is the answer. YT sells them. Ji
 
To add to advice of others....the abstraction is that a complete combustion cycle on one cylinder involves 720 degrees of crank rotation and the piston passes thru TDC twice during that.

But only one of the TDC points is correct for setting the ignition timing.

Another way to look at it is that the camshaft runs at half the crank speed via gearing (or timing chains in other engines). And so the cam needs to run a full revolution for the same complete combustion cycle.
 
(quoted from post at 19:49:10 02/08/19) Finding top dead center piston # 1. My 1940 Model A has a sheet metal pointer attached to the flywheel cover instead of the cast pointer.
heet metal pointer attached to sheet metal inspection cover is correct for 1939 and early? 1940 Farmall A's.

In order to find TDC you can also pull the valve cover and make sure both valves on #1 are closed. Then it's a simple matter to use the crank to raise the #1 piston fully. Personally I use a long thin screwdriver to check TDC having not found the mark on the flywheel the last time I looked for it. It'll get you within a couple of degrees. A dial indicator would set it exact.
 
if you have valve cover off...to verify you are compression stroke of #1 cyl. or any cylinder you can watch the running mate for that cyl. , which will be # 4 cyl. for #1 cyl. very handy when setting valves. the running mates valves will rock the same when you rock the crank. rock the crank so those valves are closed. do the straw thing in #1 plug hole to get piston in center of travel on crank at tdc then you can verify your timing marks also.
 

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