[Canada Jeff]

After I replaced me blown hose, I was heading home from my buddys dock ( 5 min). once I got home had it idle while I gathered my ropes and fenders, I herd a knocking like sound. It wasn't constant or timed. I lifted my hatch and it became more evident. If I rev it up just off idle its gone. If I switch on my silent choice its gone completely. It sounds like my thew shaft, but that wouldn't change if the exhaust was on or off. The engine got hot but did not exceed 240. I'm changing plugs this afternoon. Anything else I could check if the plugs don't help?

 

[Speedwake]

I think you should pull the fresh water pump off and check it. The impeller will go bad within about 30 seconds if it is run dry. I would start there. Your engine should never get to 240 degrees. Perhaps the sound went away because it was drowned out by the exhaust???

 

[Canada Jeff]

The hose blew after the sea pump, it never ran dry. I think you read me wrong, when I switch the silent choice ON it disappears. You can hear the knocking only when the exhaust is open, from the engine comp, and from the back outside.

 

[Speedwake]

hmmm......

I am concerned about your engine getting up to 240 degrees. I am not sure how hot the HP500's run, but my 496/HO never gets over 170...

- jeff

 

[hotbeek]

I have and have heard diverters go bad. It sounds like a rod knock. Can you narrow down where the sound is coming from ? If it's a diverter you can actually feel the exhaust and feel the knock. Diverters wear out/go bad and develop slop. At idle there is not steady pressure on them so they'll knock/rattle. Hopefully this maybe the case ?!

 

[Canada Jeff]

That could be because I can feel it on the header, it also sounds like only one side and from the back. That would also explain the noise when open. What do you mean go bad, what happens to them. How can I test this thery with out disasembly?

 

[OldMagicfloat]

I am with Jeff,your engine should not get to 240 degrees.The knock noise (might )be in the exhaust. What kind of tips do you have? Do they have flapper valves in them? It is possible you have an exhaust leak,possible riser gasket,causing a tick.Also,at 240 degrees your engine might be starting to detonate.(causing a tick noise) I would 1st ck out why it runs so hot.

Good luck,hope it's minor,and keep us posted

 

[Canada Jeff]

The only time it got hot was when I blew the hose and lost water presure. the alerm sound and I shut it off. It normaly runs at 150. The exhuast is stock, not sure the make but there is a electric valve for the silent choice. Like hotbeek said, I could see it being those valves, I hope!

 

[obnoxus]

Right,,,, you shouldnt be over 175 degrees. Trust me when I say, noises in boat motors are hard to chase!!! i switched to a K and N filter last year and pluged my breather temporarily thinking it would blow oil,,, well my old 454 drew a vacuum on my breather !!!! I thought I hurt a lifter becouse I heard a tick after that. The motor ran the same for another season and a half !!! I finally found my tic when I pulled the motor to put in the 502,,,,,,,, A damn exhaust leak !!!!!!

 

[hotbeek]

Some diverters have a rubber seal or flap around the outside, that gives a better seal. If you were to run hot(without water) you may have burnt that seal off. I did this on my motor. disassembly is really just hose clamps pretty minor. I just left mine. It did not really bother me. If you have any chance of reversion (big cam, low exhaust, beaching with transom exposed to waves etc) It may be wise to replace.

 

[Canada Jeff]

I understand hotbeek, that makes sense, and now that you have described it I recall seeing a valve apart before a long time ago.
I'm going to try and leave early today and pull in off before it rains, hopefully I will be replying tomorrow with a thumbs up!

 

[Canada Jeff]

Instead of talking about this on two threads, see blown hose .

 

[obnoxus]

Thats ok,, we need the posts !!!