Because they have dual valve springs with an inner and outer spring. Plenty of people have freshened 500's and discovered they had 3-8 cracked or broken valve springs with no real running issues. At 400hrs, it definately needs to be done anyway.

Sounds like you are looking for a simple answer, I don;t think you are going to find it here.....however talk around and soon enough someone will tell you to just run it and maybe you will feel better????

Bottom line is you have a BLUE engine, yes Merc racing......very well known for breaking valve springs. You are 150 hours over the service mark, and when it drops a valve at 5000 rpm you are going to haver huge problems.

Find a good builder to freshen that engine and pressure test those CMI's. While it is out you will have a clear look at everything else that should be inspected IE: Coupler, flywheel, gimble bearing, u joints, pulleys, and sea pump.

Not sure what your noise is, but at 400 hrs consider it a warning shot form the boating gods......believe it or not they may be trying to save you money.

Sounds like you are looking for a simple answer, I don;t think you are going to find it here.....however talk around and soon enough someone will tell you to just run it and maybe you will feel better????

Bottom line is you have a BLUE engine, yes Merc racing......very well known for breaking valve springs. You are 150 hours over the service mark, and when it drops a valve at 5000 rpm you are going to haver huge problems.

Find a good builder to freshen that engine and pressure test those CMI's. While it is out you will have a clear look at everything else that should be inspected IE: Coupler, flywheel, gimble bearing, u joints, pulleys, and sea pump.

Not sure what your noise is, but at 400 hrs consider it a warning shot form the boating gods......believe it or not they may be trying to save you money.

I know I know. It is getting valve springs tomorrow. The reason I am asking is if I can do it without pulling the motor for no reason hen I will. I will report back on how many if any valve springs are broke.

Anyone wanna take a guess on how many are broken? I'm gonna guess zero. The boat has 400 hrs with 230 of them under 1k rpm.
The winner gets 1 million dollars

you can do it without pulling the engine or even the heads, using a leakdown tester to pressurize the cylinder and float the valves.

However, at 400 hrs I will just pull the heads, have them done and inspected.

Pressurizing the cyl pushes the valves closed ,,,,not floats them.

sound like its in the valve train,,that ping sound,,is what my engine made when a push rod popped out from under the rocker arm,,,lifter was bad,,,valve spring and rocker where ok,,ez fix

In this case you are "floating" them on a cushion of air to change the spring

Sheared the heads off. Like others have stated, most likely in the upper end and it is due for a top end job anyway.

Service time. If you what to play you got to pay.