by 250_Sprint » Fri Jul 08, 2022 10:37 am
Assuming your timing cam is in serviceable condition, seated or aligned properly with the crankshaft, rotor, and end play is within tolerance, setting the ignition timing should be obtainable.
I am aware you have done this procedure many times, but you need to walk away for awhile, clear your minds eye and look at this with a fresh perspective, or aggravation will cloud your progress.
The following worked for me.
Remove the head and secure the cylinder using spacers or washers and a nut. The cylinder can’t be allowed to move up and down when the piston moves up and down.
You must be absolutely positive your piston is at Top Dead Center. Raise the rear wheel, shift the transmission into 3rd and rotate the rear wheel in the direction of operation until the piston is at its highest point of travel. Once you believe you have found TDC rotate the rear wheel in the direction of operation and in the opposite direction of operation until you are absolutely positive the piston is at TDC.
These old eyes need some help in seeing so I used cheater glasses and a light source to find TDC.
Once at TDC notice how the piston can stay at TDC yet the crankshaft can be rotated in the direction of operation and in reverse direction of operation. Rotate the crankshaft in the direction of operation until the piston first achieves TDC then stop rotating the crankshaft.
I have a digital caliper and I set the display to read in fractions of an inch. I placed the base of the caliper on the edge of the cylinder and extended the depth probe down to the top of the piston. The digital readout showed a number and I set the display to zero.
Then I rotated the rear wheel in the reverse direction of operation until the piston was lower than 13/64th”. I then extended the caliper depth probe until it was 13/64th”. Placing the base of the caliper on the top of the cylinder with the probe extended 13/64th” into the cylinder, I rotated the the rear wheel in the direction of operation until the top of the piston just touched the depth probe of the caliper. This is where the points should just begin to open causing a spark at the spark plug.
To find when the points just begin to open, I used a digital multimeter and set it to the continuity test on the auditable option. This test is used to test if a single wire is one continuous wire and has no breaks or opens in its length. When touching one multimeter probe to one end of a wire and the second probe on the other end of the same wire, the multimeter makes a beeeeep sound.
I placed one probe on one side of the points and the second probe on the other side of the points. When the points are closed the meter would beep. When the points opened, the beep would stop.
So now, I rotate the rear wheel in the direction of operation and the meter is beeping since the points are closed. I continued to rotate the rear wheel in the direction of operation until the meter just stopped beeping. The points are now open, causing a spark at the spark plug. To make sure the points are just opening, I rotated the rear wheel in the direction of operation and in reverse direction of operation in the vicinity of the multimeter beeping then not beeping until I found the exact spot where the points were just opening. Now I measured the distance from the top of the cylinder to the top of the piston with the depth probe and the caliper set to fractions of an inch and the caliper should display 13/64th”. When it did not, I set the piston to 13/64th” BTDC and rotated the points plate.
I did this procedure many, many, MANY times until I was getting no beep at precisely 13/64th” BTDC.
It was a lot of work. It required patience and time. It all worked out and my engine is starting easy, idles nice and responds as it was initially designed to 74 years ago.
Digital multimeters and digital calipers are inexpensive tools these days. A ruler and a test lamp can also be used but will be less accurate and require additional time spent reading the measurement.