How to read basic timing on 4 stroke?

[30minstokenai]

It’s possible my 40hp 4 stroke has jumped a cog on the timing belt. I’ve lost psi in all 3 cylinders.
Wondering how to read basic cam timing alignment.
If I align the cam gear triangle to the matching triangle on the head, the crankshaft position sensor aligns with somewhere around 5 or 7 on the crank pulley tape… but how would one legitimately align this for basic ensurance it’s not jumped?

 

[30minstokenai]

it’s a 1999 3cyl 4 stroke merc, carburated.
I believe the model is a M40.

 

[boscoe99]

What is the serial number?

 

[Mc Tool]

Google up the service manual . Sounds to me like .... if you have lined up the correct marks on the cam pulley the crank should line up with TDC mark not 5-7 . Its not common for a cambelt to jump teeth unless the belt is loose or damaged . Its more likely that the belt has been fitted wrong but the damage would be instant ( like the engine would not run at all ) so if it crapped out on the move it may have jumped a tooth or two but there would have to be a reason . what condition are the belt and tensioner pulley in ?
there arnt to many reasons youd loose comp in all cylinders but off cam timing and subcequent bent valves would do it
If you can remove the valve/cam cover and check valve clearances . If your finding large valve clearances usually means the valves are bent and wont close ( hence the large clearance and no comp ).
youd have to be real unlucky so have a look at the manual.