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Hi everyone. Its been awhile since I have posted anything of substance so I thought this would be appropriate with all the talk about TDC.
79xs11sf's thread "True Tdc" got on to other things but I recently turned 30K miles and did some cam checking with a degree wheel and dial indicator. I have started to write up my findings to post here on the forum but I am not finished all that yet since I plan to tinker with some cam timing. But, the next paragraph is what I had written down so far about finding true TDC.
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Top Dead Center on the #1 piston at the very top of the compression stroke. Locating TDC is critical to your measurements since everything is measured off of the crankshaft. Also, as little as one or two degrees can have an effect on your cam timing. Some use a soda straw in the spark plug hole and rotate the crank until it stops rising out of the hole to locate TDC. BUT, this method could leave you several degrees off because of piston dwell at the top of the cylinder while the crank throw and rod swing past TDC. So I used a piston stop and degree wheel instead. I installed a wire pointer and degree wheel as close to TDC as possible (using the timing plate as a reference) and then I installed a piston stop on the spark plug hole on the #1 cylinder. I ROTATED THE CRANK to just before TDC (about 20 degrees) and screwed the stop in until it just touched the top of the piston. I recorded the reading on the degree wheel and then ROTATED THE CRANK the opposite way around until the piston touched the stop again and recorded that reading. Then I added the two numbers together and divided by 2 and recorded the answer. I RELOCATED THE WIRE POINTER to line up on the degree wheel with the mark that represented the answer. To check, I ROTATED THE CRANK in the opposite direction until the stop touched the piston again and verified that the pointer was on the exact degree on the opposite side of TDC. If it does not come back to the same degree on the opposite side of TDC, start over. If it does, then simply ROTATE THE CRANK until the pointer lines up with zero on the degree wheel and that is true top dead center. Make sure you do not bump the pointer while you work.
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This method works every time, is easy to do and puts you dead on the mark. It only took about ten minutes to set up. Naturally, if your valve cover is not off so you can see the cams you need to make sure you are coming up on the compression stroke by placing your finger over the spark plug hole while you rotate the crank. When you feel the compression coming out past your finger you are approaching TDC. If you dont have a piston stop you can easily make one with a bolt and an old spark plug body. If you do not have a degree wheel, type 'motorcycle degree wheel' on Google and you will find some that can be downloaded. Print one up on sticky paper and make one on a piece of heavy cardboard or sheet plastic. A 6" or 7" diameter wheel is perfect and gives you enough clarity between marks to set up down to 1/2 a degree. A pointer is a simple as a piece of wire with a point that is bolted to the engine block. I used a wheel by MotionPro. If you have such a degree wheel that can take high RPM, you can set your ignition timing very accurately too.
79xs11sf's thread "True Tdc" got on to other things but I recently turned 30K miles and did some cam checking with a degree wheel and dial indicator. I have started to write up my findings to post here on the forum but I am not finished all that yet since I plan to tinker with some cam timing. But, the next paragraph is what I had written down so far about finding true TDC.
_________________________
Top Dead Center on the #1 piston at the very top of the compression stroke. Locating TDC is critical to your measurements since everything is measured off of the crankshaft. Also, as little as one or two degrees can have an effect on your cam timing. Some use a soda straw in the spark plug hole and rotate the crank until it stops rising out of the hole to locate TDC. BUT, this method could leave you several degrees off because of piston dwell at the top of the cylinder while the crank throw and rod swing past TDC. So I used a piston stop and degree wheel instead. I installed a wire pointer and degree wheel as close to TDC as possible (using the timing plate as a reference) and then I installed a piston stop on the spark plug hole on the #1 cylinder. I ROTATED THE CRANK to just before TDC (about 20 degrees) and screwed the stop in until it just touched the top of the piston. I recorded the reading on the degree wheel and then ROTATED THE CRANK the opposite way around until the piston touched the stop again and recorded that reading. Then I added the two numbers together and divided by 2 and recorded the answer. I RELOCATED THE WIRE POINTER to line up on the degree wheel with the mark that represented the answer. To check, I ROTATED THE CRANK in the opposite direction until the stop touched the piston again and verified that the pointer was on the exact degree on the opposite side of TDC. If it does not come back to the same degree on the opposite side of TDC, start over. If it does, then simply ROTATE THE CRANK until the pointer lines up with zero on the degree wheel and that is true top dead center. Make sure you do not bump the pointer while you work.
__________________
This method works every time, is easy to do and puts you dead on the mark. It only took about ten minutes to set up. Naturally, if your valve cover is not off so you can see the cams you need to make sure you are coming up on the compression stroke by placing your finger over the spark plug hole while you rotate the crank. When you feel the compression coming out past your finger you are approaching TDC. If you dont have a piston stop you can easily make one with a bolt and an old spark plug body. If you do not have a degree wheel, type 'motorcycle degree wheel' on Google and you will find some that can be downloaded. Print one up on sticky paper and make one on a piece of heavy cardboard or sheet plastic. A 6" or 7" diameter wheel is perfect and gives you enough clarity between marks to set up down to 1/2 a degree. A pointer is a simple as a piece of wire with a point that is bolted to the engine block. I used a wheel by MotionPro. If you have such a degree wheel that can take high RPM, you can set your ignition timing very accurately too.
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