Timing a small 4-stroke?

[flyweightnate]

Long story short, I took apart a 40cc motor before I realized they didn't put timing marks on the crankshaft gear, like I'm familiar with.

Does anyone have advice on how to figure out where to put it? There are marks on the flywheel, and the camshaft timing mark coincides with the cam. I was going to set the cam at 180 degrees from the valves, and put the flywheel line as shown so it should have just crossed the coil. Hoping to get this dumb thing working...

"Earthquake Viper" tiller MC440 with overhead valves.

[markdem]

Ive never dealt with cams like that, so i find them a little confusing, however i would measure the pistons top-dead-center instead of relying on timing marks alone

[flyweightnate]

Ive never dealt with cams like that, so i find them a little confusing, however i would measure the pistons top-dead-center instead of relying on timing marks alone

That's the weird thing - the flywheel is keyed, and definitely not hitting spark at TDC.

But you'd say time it "centered" on TDC?

[markdem]

I never learned a whole lot about ignition systems (because they rarely broke) but i dont think the magnet on the flywheel has to line up with the coil

The spark actually occurs after the magnet and coil have passed each other. Ignition coils create a spark when they loose voltage, not when they gain voltage. So dont worry about the magnet lining up with the coil

[JeeperCreeper]

It's best to put the piston on top dead center, and you want the cam where both valves are closed. The next valve that should open after that is the exhaust valve, so the lobe should be about 90* from hitting that exhaust valve at TDC

[JeeperCreeper]

The cam rotates at half the speed of the crank, so 180* or one stroke of the piston equals 90* of cam rotation. After TDC, the piston goes down, moving the crank 180*, and is now ready to push exhaust gas out through the now open valve.

[JeeperCreeper]

Oh and next time use a punch and make your own timing marks

[flyweightnate]

Yes... this is the best comment so far.