2002 50hp bigfoot 4 stroke compression issue

[got2haveit]

I,m working on a 2002 50hp bigfoot that was running fine and then just stuttered and stalled. Was towed to dock and will start but runs rough. Checked compression and all 4 cylinders are at 100#.This is way below the 180 to 210 spec. It seems like the head gasket blew. There are no apparent leaks or visual signs of a problem. What can it be?

 

[racerone]

And how does a head gasket blow in 4 places at once ??------Checked oil ?---------Checked timing chain / belt on this motor ?-------Was throttle open during compression test ?

 

[got2haveit]

The oil was fine with no noticeable leaks, the timing belt seemed to be in good shape. The throttle was at the neutral position.

 

[got2haveit]

Still trying to figure out how compression dropped to a consistent 100# on all 4 cylinders. I used 3 different testers to confirm it. Any ideas on what could have happened would be appreciated.