HEar valves when hot but not until then.  By  Deleted (Read 2,137 times)

Tdc is when they are both evenly and fully open and can be set exactly

I here some of these bikes are notorious for being off TDC marks etc and the only real way to verify that the lobe of the cam is at its highest is to simply observe it.

Right, If you want to be sure, remove the fan cover. There will be a protrusion on the case. You rotate the flywheel until the T mark on it aligns with the protrusion. This indicates that the crankshaft and piston are in the top-dead-center position. Now, with the valve cover removed, you look at the cam sprocket. It has at least two sometimes three holes. One hole is larger than the others. This hole should be directly up or at degrees(pointing away from the cylinder) in other words, the same direction as the piston travel. The other holes should line up with the top of the head. If not, the cam is not in sync with the crank, you may have to jump a tooth. When piston and cam are in the TDC position, both valves are fully closed, and you can set them

This is true,Rocky. However, If the cam shows TDC. ,and the piston is not, the engine will not time properly. Best to check both.Top Dead Center refers to the piston, which IS indicated by the flywheel. Cam and crank need to be synchronized.

You aren't impacting the relationship between the crankshaft timing gear and camshaft timing gear when adjusting the valve lash so flywheel timing marks are not really critical to the operation and are only a secondary check to verify that the timing chain has not skipped a tooth.

If you removed the cam shaft and need to set a new one then put the camshaft at the timing marks and verify TDC at the flywheel while installing the new cam being sure to refrain from rotating the flywheel while its apart and loosing orientation or dislodging the timing chain from the crankshafts timing gear.

If your only checking valve lash with no other symptoms of valves being out of sync then there is no real need to open up the flywheel to check tdc which will also be apparent via the spark plug hole which will be opened anyway to ease lining up the the camshafts timing marks.

After almost 50 years working on small engines you learn what is really needed to check valve lash and symptoms that would indicate any further checks are required.

However there will be other symptoms that would indicate the need for verifying the timing chain. Been at this almost half a century now and can tell when a timing chain has skipped a tooth and needs to be checked. It will be very obvious in the way the engine is running that the chain has skipped a tooth and needs to be checked.

If you can't tell then by all means check flywheel TDC, personally it is pretty obvious when it is and is not set correctly.

All done and told the more critical check when setting valve lash is at the cam gear. Check both if you wish but don't just go by the flywheel mark when checking valve lash.

Note that if the marks don't match up you could have a damaged woodruff key or a timing advanced key on the flywheel so don't be too quick pulling the cam and resetting the timing chain before your verify the condition and type of key on the flywheel.