Camshaft By FACE PLANT FOR LIFE (Read 572 times)

[FACE PLANT FOR LIFE]

Hello everybody. So we're reassembling my dad's bike, and we're following the instructions to the T, unfortunately my dad refuses to continue putting it back together until he thinks everything is "perfect". Does the position of the rotating parts of the camshaft matter in relation to the camshaft assembly?

[tvnacman]

remove the fan cover line the "T" line to the pointer , then line the lines and holes on the cam gear . your done .

your welcome to Skype , I don't know how much longer I will be home .

John

[Alleyoop]

1. Rotate the motor by hand and line up the "T" on the FLYWHEEL with the pointer in the CASEING like in the picture.
2. Then If you took off the CAMSHAFT already line it up like like In the picture.

Alleyoop

Now when you put the cam back on and chain the marker may move from the "T" it is OK if the pointer is a little "BEFORE" the "T" .. BUT NOT AFTER THE "T" closer to the "F" MARK(NO GOOD).

[Bashan]

I'd like to offer a few of my own thoughts on this topic. If you've ever tried to set the piston at TDC for cam installation you know how frustrating it can be. The piston will move very little while the flywheel is...well...flying back and forth past the "T" (top dead center)mark. There's a reason for that (you knew that was coming didn't you?). I have a diagram (you knew that was coming too didn't you). When the piston is at the top of the stroke the connecting rod journal is moving almost horizontally as the red arrows illustrate on the middle of the diagram.

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That means there's little vertical travel of the piston (blue arrows) but lots of rotation of the flywheel. I've never like the top dead center approach either for setting valves or installing the cam. There's too much flywheel movement for the piston travel. FYI, the converse is true when the piston is headed down (right illustration), there's lots of piston travel and less flywheel rotation.

The camshaft is geared down from the crankshaft, it turns half as fast. That's why the cam sprocket timing marks are oriented correctly for timing on one revolution of the crank but not the next. So when you're installing the cam make sure the flywheel mark is on the "T" and all three holes on the sprocket are visible. Having said that, if the cam sprocket is geared down, the crankshaft is geared up from the camshaft and turns twice as fast. That's why a little movement on the cam chain while trying to install a cam is a lot of movement on the crank/flywheel/timing marks. That's why the "T" mark is not going to be perfect on the timing tab, there's too much tolerance built into the system. I will say this again, to install the cam sprocket oriented incorrectly it would have to be WAY off. That's because you'd have to jump a whole link and that would be a boatload of flywheel travel. The "T" mark would be way off, not drifting one side or the other of the tab. By the way, there is no consistent deviation of the timing marks on GY6s, each batch has their own mark deviation.

From what I've gleaned from reading several articles on the timing marks, the "T" stands for timing. It seems that at one time the engines could be timed and was done with a timing light. If you're too young to know what a timing light is I hate you. Now get the hell out of my yard you whippersnapper! Anyway, a timing light is simply a strobe light that you hook into the ignition. Then you point it at a timing reference, the tab next to the flywheel in this case, and set the timing so that the reference mark (the "T") is correctly oriented to the tab. Since most things are electronic these days and time themselves, the light is a dinosaur. The "F" seems to stand for firing or fire. I'm not sure this is correct so if somebody has a thought on this I'd like to hear it. I'm sure you know that the spark plug fires before the piston hits TDC. They call this spark advance. That's because the gas/air mixture has to have a chance to combust before the piston starts heading back down. If the combustion had to chase the piston down the cylinder you'd lose half your power. Well the "F" mark is, from what I read, when the trigger coil sends an impulse to the CDI to initiate the spark. You can see on the left of the diagram the "F" mark does it's work before TDC. There is a flaw to this postulation however, the spark advance increases as the RPMs rise but the F mark is static. Maybe the CDI compensates, I'm not sure.

Also, you may want to check out this thread.