Model 31P677

My 19.5 B&S 31P677 won't turn over when it's coming up to TDC, good battery, good starter, valves adjusted. I've read where there's a compression release on the camshaft, I need to know if this may be my problem and if it is can this part be replaced or do I have to replace the camshaft?
Thanks for any help with this,
Dave

Model 31P677