Honda GX620 no-start question

[klindstedt]

I have a Honda GX620 (GCARK-1111412 type QAFX) that got overheated, made the cam gear brittle and it broke. I replaced everything that was a plastic gear (oil pump, governor) with new OEM parts except the camshaft. I used a generic version, but matched up to the old and everything looked to match. Got it all buttoned up, filled with fresh 10W-30 synthetic oil, and new oil filter. It was a little hard starting the first time, but did finally catch and ran fine for a 1-1/2 hour mowing session (this engine is on a Grasshopper ZTR). Got it back in the garage and was ready to mow this week, but again had hard-starting issues. Took the air filter off, gave it a little starting fluid, and no joy, not even a pop. As I kept playing with it, I started getting backfires out the carb and the elbow into the carb was wet with gas. I've deduced that I have an intake valve stuck open.

But this it the part that puzzles me - when cranking the engine over, there is no rocker/valve movement. If I rotate the engine by hand in the reverse direction, the valves open and close as expected. My first fear was the cam gear broke again, but not possible if the valves open 'in reverse'. What am I missing here? Thanks in advance for your help.

[SUKI]

Just because movement backward turning doesn't mean a lot as have tried going the right direction. A sheared key can hang just enough in reverse to move things.(Ratchet effect). So try going in the right direction and see what happens.

[klindstedt]

As I stated in the original post, forward rotation results in no valve movement. I don't see how a sheared key could be relevant here, the camshaft is gear driven right from the crank. A sheared or partially sheared key could effect ignition timing, but not valve movement, right?

[bgsengine]

As I stated in the original post, forward rotation results in no valve movement. I don't see how a sheared key could be relevant here, the camshaft is gear driven right from the crank. A sheared or partially sheared key could effect ignition timing, but not valve movement, right?

Possibly may be thinking of a crankshaft gear key, which many engines will have if it is not noticed (especially if ball bearing crank bearings) it's easy to overlook.

[38racing]

As I stated in the original post, forward rotation results in no valve movement. I don't see how a sheared key could be relevant here, the camshaft is gear driven right from the crank. A sheared or partially sheared key could effect ignition timing, but not valve movement, right?

As said possibly flywheel is not turning crank which then doesn't cam in forward but flywheel does turn crank in reverse.

[klindstedt]

As I stated in the original post, forward rotation results in no valve movement. I don't see how a sheared key could be relevant here, the camshaft is gear driven right from the crank. A sheared or partially sheared key could effect ignition timing, but not valve movement, right?

Possibly may be thinking of a crankshaft gear key, which many engines will have if it is not noticed (especially if ball bearing crank bearings) it's easy to overlook.

Ahh.. gotcha. I can check if that is the case here. I did not notice a key, but then again I was not specifically looking for one.

[klindstedt]

Well, found the problem this afternoon. The aftermarket camshaft now has half the gear teeth it started with. Worked great for one mowing, but failed the second time I tried to use it. I should have known better and just bought the OEM part to begin with. Thanks for the comments and suggestions.