I was pre fishing for Champs today and the motor started making a knock running across the lake. I instantly shut her down and checked all gauges. Started it just to see if [censored]-hole was spitting water and it wasn't. Got a tow back and removed cover the spark plugs had been loosened and oil seeping from all 6. Used a scope and all Pistons are intact. About to run a compression test, my question is: is it possible to not have serious head damage if the comp test checks out?

You should have 90 pounds on all 6. If the plugs are all loose, it probably got way too hot.

what motor?,,,,,

if a V6 merc 90 lbs ain't gonna be enough.. rattle/knock may not show with justa comp or leak down..
did ya tighten up tha plugs, try ta start?

It's an 06 Yamaha vmax HPDI. It started raining out so I haven't had the chance to do the comp test but I know they should all be around 115 or at least within 10% but I'm concerned with how hot it must have gotten that a compression test may not show the full extent of the damage.

most everything Yamaha leaves me in tha truck but I do know a rattle and or knock may not show with a comp test on any of 'em.. there's lotsa bearings and stuff that won't effect comp....but heat will effect all of it. usually but not always pistons first.. there's some rice guys on here that might have tha answer for ya.....gl n hope it turns out minor..