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Loud Mechanical Ticking on 2001 Mastercraft X30 with Indmar 5.7L Predator 310 Engine

G

GCX30

New member
Help! I can't figure this out and my marina's mechanic has been too busy to get to it. Season is short here in Chicago! : )

On our second outing of the year (first outing was short), after driving around slowly for a couple of hours, the boat started making a very mechanical sounding ticking noise only when moving faster. Here are the details:
  • It makes that noise at around 2,500RPM and higher, only when under load. It also increases with higher RPMs. There is no noise at idle speed or when revving the engine in neutral.
  • The riser gasket seems to be failing a bit on the port side (white residue streaking down from the seam from the manifold to the riser) but there is no sound coming from that area, and no exhaust gasses escaping.
  • It sounds very clearly like it's coming from the front of the engine (the stern of the boat) by the belt and accessories area.
  • The alternator and brackets feel tight. The belt feels tight enough (I'm not a mechanic but it didn't feel "loose")
  • The oil is clear and full. Transmission fluid is perfect.
  • Wiring to the spark plugs is relatively new so I don't suspect any electrical arching.
  • Engine performance is perfect. No hesitation. No loss of power. Easy starting.
  • I took the flame arrestor off and there's no sound coming from the valves or injectors and they seem to be functioning normally.
Here’s a video where you can hear it:


Would really appreciate any expertise you can provide! Hopefully I can fix it myself. Thanks in advance!
 
I have this exact same noise started on my 2001 X9 last week, I suspected a manifold gasket (im a hgv mechanic so have a mechanic background) i think you call that a heavy diesel mechanic in the U.S (im in the UK) anyway did you manage to get it sorted and was it just a gasket if so? Hoping to last the season on it and tear it down in the winter if needs be.... by the way mine runs solely on lpg so rules my fuel system out
 
Two adjacent cylinders were low on pressure. They removed the top and said that I needed new heads and gaskets. However, they couldn't tell me for sure if that was the only problem and recommended a new (rebuilt) engine based on the risk of doing all of that work on a 25 year old engine and there being other issues. I'm most likely going to sell it as is to someone who can fix it.
 
When it went from the high idle speed to low idle at the end of the vid I didn't hear the ticking anymore. That to me suggests a possible exhaust leak.
2 low adjacent cylinders could be a blown head gasket, depending on where it blew, it could also create an exhaust leak so it could all be related.
It would have been best to do a leak down test before removing the cyl heads
If the condition of the block deck surface looks good, it might be worth the risk of installing a set of reman cyl heads and all new gaskets. I did that with my 1988 4.3 V6 about 9 years ago and it's still OK as far as that goes, good compression, no water in the oil etc.
Blown head gaskets suggest that your fuel octane may be too low, timing too far advanced, or boat is over propped. If anyone is going to be fixing it those issues have to be looked at or else you can have a repeat problem.
 
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