camshaft slides forward

[rob7.3]

02 exp 4.0, replaced all timing chains and put back together and it started sounded good. Coolant leak at thermo housing shut it off and fixed but now it won't start. Pulled everything down to find the can had moved forward again off the rockers. This is the second time its moved. What am I missing? Can't figure it out. No thrust washers, plasti guage check shows its in specs. Any ideas or suggestions please.

 

[2000StreetRod]

Thrust bearing cap

The front bearing cap on the left (driver side) camshaft and the rear bearing cap on the right (passenger side) camshaft act as a thrust plate to keep the camshaft in position.

Notice in the photo that it is wider than the other bearing caps.