4.5 HP Yardworks Mower

My guess is that when you pulled the case apart that something came loose and didn't go back together right. Probably something around the cam or pushrod area.

Oil Splasher Fork is connected on Briggs engines at the connecting rod clamp bolts. If it is put on 180 degrees the opposite way on the two clamping bolts the bend in the fork points it the other way 180 degrees that may hit something inside the crankcase.

Just to see if it rotates once you have found something out of place or what ever, I'd have the spark plug out just so it is easy to turn by hand and watch the cams push the tappets and so forth. Even with the crankcase cover still not on it may be possible to do this.

Before you open it you could just take the spark plug out and see if there is still resistance.

Maybe the splasher fork is not clearing the additional feature that you added to convert the engine vertical to horizontal shaft?

If you can take pictures a lot from when you make changes or take something apart you are not familiar with. Even stuff I am familiar with when I take picture to be sure I put something back after making changes, I may have something in the photo of something I did not see out of place.

The dot and the two slash mark line up for the cams gears to be in the right line up, so the timing is right, I'm not sure it would cause this to be hard to crank, but it would make it no run or run well.

There are threads maybe here where people have done conversions, but I do know Youtube and other searches came up with them.

MT