Hey all. Replaced the cam and rocker arms in a 97 Xplorer 500 and it won't turn over smoothly. Getting stuck on compression stroke. It will go by it eventually, but not enough to start. Tried pulling it over and recoil just about busted my wrist. Wasn't thrilled with the tight fit of the new rocker arms between the towers, fit it is really tight, but they do move. The old ones moved easily and were maybe .050 inch smaller in combined width than the new. Cannot imagine how that would impact it though. Triple checked the compression release spring and weight, they are perfect. I only pre-wound spring 1/4 inch per the manual and the ball does jut out and drop as I operate the arm manually. I'm stumped. The battery and starter worked perfect with the old cam and arms, so I really don't suspect those. Today I'll try jumping it with my truck, but I'd be surprised if that was the issue. Set the timing the failsafe way, removing the magneto and stator and setting timing using the silver links. It has to be the compression release. Is it normal to hard start until the cam wears in and gets oil in there? Thoughts appreciated.

 

OK, so I tried a jump, no difference. So then I ran a leak down test with the rockers all the way off and confirmed that the valves are seating. Just the normal minimal blow-by past the piston. Triple checked the timing, it remains perfect, unless I could possibly be 180 degrees off? I don't think you can with these machines, TDC is TDC and the compression/exhaust stroke is dictated by the position of the cam, right? So then I locked the decomp release lever to the stop peg on the cam with a ziptie to make sure it remained engaged such that the ball extended outward and remained rigid and bumping the exhaust rocker/valve like it should on start up to relieve compression. I tried to turn it over with the starter, same issue, locking up right at the point where the ball bearing would contact the exhaust rocker. I put air pressure to the cylinder and could turn it over and listen to the intake and exhaust valves open and close and then when the little ball got to the exhaust valve I could turn by hand no more. Another weird thing - I can hear air is escaping the exhaust valve when it shouldn't (when I'm on the flat of the exhaust lobe) and then when I get to the decomp ball the exhaust pipe goes silent right at the point that I can turn no more. It's almost as if the ball bearing is closing the exhaust valve when it should be opening it?? Once I pulled the air, no problem turning 360 degrees, so its not a mechanical stoppage. I can feel the exhaust rocker stiffen up as the ball passes under it (no more clearance can be felt), but I am not visibly seeing it rock and question whether the ball is moving it enough to open the exhaust valves. Clearances are a perfect .006 at TDC. Maybe my understanding of the decomp system is fundamentally flawed? Am I correct that the decomp system works by the return spring causing the weighted release lever to close and push the ball bearing outward as you crank the starter, so the ball contacts and rocks the exhaust rocker arm and opens the exhaust valves a tiny bit? Then once it starts (at 350 RPMs or greater) the centrifugal force overwhelms the spring, opens the lever so the ball bearing will no longer engage the rocker? I was pretty sure that is how it works, until I heard the way the compressed air was escaping the exhaust as I cranked over the flat of the exhaust cam lobe and then went silent as the ball began to engage the rocker. I would think that I would have no problem cranking it all the way over by hand with only 60 lbs of pressure to the cylinder. Why can I turn it over past the cam lobes with air to the cylinder but not that little ball?!? Then why can I turn it over no problem with no air pressure to the cylinder? Pretty good with wrenches but this one has me stumped. Someone rescue me from this nightmare. lol