Let's start by saying I'm NOT a wrench, so I could use some help here.
Just bought the boat used w/ 158 hours on the twin 1999 HP500 Carbs. Guy I bought it from took really good care of it. Had receipts for all maintenance (25 hour oil changes, 50 hour drive oil changes, etc.).
I had the valve springs replaced when I bought the boat just to be safe.
Was running the boat at WOT for longer than normal on Memorial Day weekend (maybe 5 - 7 mins at WOT). Blew a spark plug out of the port engine and when I shut the boat down, I noticed a "knocking" sound in the starboard engine. Towed the boat in and let it cool. Checked the oil in both engines and both were within 1/4 of a quart of full. Replaced the plugs in both engines and the port engine appears to be running fine. I should say both engines were running at normal Oil and Water temp when the plug blew.
The starboard engine is still knocking or ticking. Frequency of knock increases with RPM's. I thought it would be a lifter or something in the top end, but the local mechanic pulled the boat, put the ear muffs on and ran it. He says I have a rod knocking. Never heard of a rod knocking, but this mechanic is highly recommended by several local boaters who I know and trust. Is this likely? I thought the bottom ends on these HP 500's were pretty stout.
Also, I thought you typically blew a plug when the engine gets HOT, which didn't appear to be the case when mine blew based on water and oil temp. Only thing I can think of is they repainted the lowers on the outdrives when I bought the boat. Maybe the water intakes got restricted during the repaint? How much water PSI should I expect to see at 3500 RPM?
I would greatly appreciate any thoughts on the knocking rod or the blown plug.