Finding TDC

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les king
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Finding TDC

Postby les king » Mon Oct 17, 2016 12:15 am

I read where a lot of folks stick something down spark plug hole to find TDC. I use my air hose. Remove number one plug and put pointer on pulley mark, blow air (I have a nozzle that has a rubber grommet) if there is no resistance, make one revolution on pulley back to the mark. thereshould be resistance, as valves are closed.
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Re: Finding TDC

Postby Jim Becker » Mon Oct 17, 2016 9:38 am

This procedure will tell you whether you are at TDC of the compression stroke or TDC of the exhaust stroke. It depends on having/finding the TDC notch on the pulley. Sticking something down the plug hole is a method for determining where the TDC notch should be if it is missing, obscured, or out of place.

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Re: Finding TDC

Postby les king » Mon Oct 17, 2016 1:03 pm

Sticking something down the plug hole is plan B

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Re: Finding TDC

Postby Jim Becker » Mon Oct 17, 2016 2:46 pm

les king wrote:Sticking something down the plug hole is plan B

No. They are different procedures done for different reasons. Your first step is:
les king wrote:Remove number one plug and put pointer on pulley mark, . . .

The other procedure is for when you don't have a pulley mark or the mark location is in question.

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Re: Finding TDC

Postby Winfield Dave » Mon Oct 17, 2016 2:54 pm

Very simple method from Gary Dotson Cub Tip of the Week! January 19th, 2011
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Re: Finding TDC

Postby Steve Butram » Mon Oct 17, 2016 4:37 pm

Hold your finger over the #1 hole until you feel a rush of air then look for the mark on the pulley. You should be able to see the top of the piston thru the hole with a flash light.

I'm not clear on why you would use compressed air to find TDC I would never advise anyone to stick something into the cylinder for fear you would leave something that would scare the cylinder wall
Be prepared to be unprepared Seth Goden

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Re: Finding TDC

Postby Jim Becker » Mon Oct 17, 2016 8:35 pm

I'll type it slower this time. Maybe that will help.
Gary's method determines which TDC you are on and depends on using the existing timing mark for exact positioning (same as the one Les posted). Inserting a positive stop for piston movement is the only way to exactly determine TDC. Use a screwdriver with a handle that won't fit through the spark plug hole.

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Re: Finding TDC

Postby brewzalot » Mon Oct 17, 2016 9:10 pm

Jim Becker wrote:Use a screwdriver with a handle that won't fit through the spark plug hole


Or a dial indicator if you want an exact visual reference. This is not necessary however, just neat to see it if you are one of "those" like me.

Tim


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