I was making what I expected to be one of my last runs of the year last Sunday and toward the end of my run my starboard exhaust sounded just a bit funny, as in a slight miss. As I was coming off plane into the marina I backed off and the starboard motor started making a very bad noise. It sounded like top end valvetrain inside the valve cover. Motors have Crane roller rockers and complete valve train. Could the exhaust sound I was hearing have been a stud working its way out and the really bad noise it finally coming loose and letting the rocker and pushrod lose contact with each other and breaking something ? I haven't been able to open it up yet and it ran only for an instant with the big noise.

Anyone care to suggest what might have happened ? The guys that work on my motors won't be able to look at it for 6-7 days so I'm just hoping it's not fatal.

valve seat dropped.......

Anyone can guess. I dont think a stud would back out. Just because you have pretty good parts doesnt mean they dont break. My first guess would be a broken valve spring or bent push rod. Just have to get it appart to see. At least it's at the end of the season.
Jerry.

Would a broken spring or bent pushrod happen "slowly" as in being able to hear the difference in exhaust sound for a minute or two ? I was able to hear a difference for a minute or so and only when I let off did it start being nasty sounding.

It could be a lifter going bad. They do have a limited life span. The needle bearings in the roller start to break down and clearence opens up between the lifter and the cam.

I have never seen a spring partly broke. I have seen push rods bend bad enough to come clear out. I had this happen once and it allowed the lifter to jump out of the bore. When and engine is off idle there can be allot of noise that may mask a noise you can hear at idle. If you have a roller cam it could be like PatriYacht said with added clearence between the cam and lifter. I have seen the roller or cam lobe get a bad spot which causes the lifter to skip over the cam in stead of rolling and cause a noise however what I have seen is just a clicking noise. Sometimes if a valve stops opening you can get allot of loud popping. Again untill it's taken appart it's all speculation.

Jerry.

Guys, the noise I had was like a 1/2" box end wrench was loose in a valve cover. It was big.

Could be any of several things or a combination of them. Broke rocker, broke lifter, broke stud, broke spring, bent pushrod or all the above.

No reason to guess. Just go pull the valve cover.

Hum, are you missing any tools?

I think Griff has the right approach here. Is there any water in the oil?