Hey guys,
I have a 18.5 B&S in my 42" craftsman riding mower I have replaced the starter twice the battery once, the selinoid once and I can't getthe engine to crank a full compression stroke it sounds like it wants to but the starter can't give it enough power to crank? What am I doing wrong??

Adjust the valve clearance.

How would that be done? I keep thinking that the starter or battery can't give it enough power?

Also I have about 140psi at tdc

You need to find the specs for your engine, for that provide the model, type and code from the blower housing.

Specs might be something like "0.005" Intake, 0.006" exhaust 1/4" btdc" - not your actual spec.

How this might be done is use a dial indicator in the spark plug hole and find when the piston is 1/4" before Top Dead Center on the compression stroke. The valves are then adjusted for the specified clearance. Remember, you will have intake, compression, power and exhaust.

A car is usually done differently. Usually you locate TDC with the mechanical marks on the harmonic balancer. 1/2 the valves will be loose and the other's tight. You adjust the clearance for the loose I & E valves and then you rotate the balancer 1 turn and do the others.