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Drusplanet

Bad timing

2 posts in this topic

Is there a way to set the timing on my 98 YZ400 to TDC when I don't have a stock timing cover? The bike came with a Carbon Factory cover so I've been guessing at setting the timing for the DCM mod. After numerous attempts I still can't get it right.

I have a flywheel puller now if I need to see the actual crank I can. :)

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Pull the spark plug and use a screwdriver blade to locate TDC.

The most accurate method would be to build a piston stop out of an old spark plug by welding a rod to the bottom of it so the the rod is long enough to prevent the piston going over top center. Run the piston down to near the bottom and install the stop in the plug hole. Mount a degree wheel on the crank, and attach a pointer made of wire or whatever to point at the marks on the degree wheel. Rotate the engine in either direction with a wrench until the piston hits the stop. Move the degree wheel to indicate zero. Rotate in the opposite direction to the stop and read the degree wheel. Move half of the indicated reading toward zero. For example, if the wheel indicates 50 degrees as it hits the second stop, move the wheel so it reads 25. Rotate it back in the first direction and check the reading. It should be 25. Make corrections as needed to make both numbers the same when the piston stops in both directions. Remove the stop, and the indicated Zero will be exactly TDC.

You can do very well with this method without building a hard stop by substituting a screwdriver that's too short to reach BDC, but hits the piston before TDC. Match up the readings in both directions from TDC at the point where the screwdriver looses contact with the piston, then make permanent marks so you don't need to repeat all this.

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