Odd clinking sound at WOT

[boatdiver2011]

Hello all! I have an issue I just can't figure out. I have an '84 Merc 470. When I run WOT, I have a "clinking" for lack of a better term. It is only there when under way, and only at 3000 rpm (which is all I get out of her). It is not in time with the motor, but random. I just had the motor out last year for a rebuild of the cam shaft seals, and the motor is beautiful inside, and still tight. (no lifter slop, timing chain tensioner, etc.). I had a friend at the controls last night while I poked around the motor. The sound is best heard near the starter/ heat exchanger. Is it possible for a spring in the starter to weaken and allow the gear to bounce off the flywheel? I have gone through everything else and can't even find a loose bolt!
Your thoughts would be much appreciated!

 

[Bondo]

Re: Odd clinking sound at WOT

Hello all! I have an issue I just can't figure out. I have an '84 Merc 470. When I run WOT, I have a "clinking" for lack of a better term. It is only there when under way, and only at 3000 rpm (which is all I get out of her). It is not in time with the motor, but random. I just had the motor out last year for a rebuild of the cam shaft seals, and the motor is beautiful inside, and still tight. (no lifter slop, timing chain tensioner, etc.). I had a friend at the controls last night while I poked around the motor. The sound is best heard near the starter/ heat exchanger. Is it possible for a spring in the starter to weaken and allow the gear to bounce off the flywheel? I have gone through everything else and can't even find a loose bolt!
Your thoughts would be much appreciated!

Ayuh,... Welcome Aboard,...
My guess is, yer hearing Detonation,...
Probably runnin' Lean,...

Any Crud in the fuel Filters,..??

 

[boatdiver2011]

Re: Odd clinking sound at WOT

Bowl filter on the fuel pump is on my routine maint. list every spring, so it is clean, as for the filter in the carb, can't say. I have ordered a rebuild kit for the carb, and figured I do it all at once. Thanks for the advise, I would have not thought of that one! I think I'll leave her ashore until I finish the carb rebuild!

 

[bellhop]

Re: Odd clinking sound at WOT

At WOT I believe that noise would be money falling out of your pocket into the fuel tank.

Probably not much help huh? Sorry.

 

[Bondo]

Re: Odd clinking sound at WOT

At WOT I believe that noise would be money falling out of your pocket into the fuel tank.

Probably not much help huh? Sorry.

Ayuh,... Actually,.. it's a Lack of gasoline available to the motor at Wot,...

 

[boatdiver2011]

Re: Odd clinking sound at WOT

No I located that noise- took me a while to figure out the screaming from the console. Then yesterday the screaming was coming from my pocket- yep my wallet screams louder the farther I push the throttle! With these prices, I will keep my trusty 470, ya all can keep them bigger motors!

And thanks again Bond-o. Just curious, mine has not been doing it for long so I am not worried about damage and she is now land locked until the carb rebuild, but what damage could this do to a motor?

 

[Bondo]

Re: Odd clinking sound at WOT

but what damage could this do to a motor?

Ayuh,.... Usually as the sparkplug tip erodes, a Huge Hole forms in the Piston....

Detonation will turn a boat motor into a boat Anchor is No Time Flat....

 

[boatdiver2011]

Re: Odd clinking sound at WOT

WOW- Well I heard it for the first time when I ran it the second time this year. Took her out trying to figure it out last night, so only about 2 maybe 3 hours total run time, maybe 1 hr WOT. Think I'll pull the plugs and see if I can see anything through the hole. I really don't want to tear her down at this point, well- default to someone who knows more about it- should I be worried enough to tear the motor down for inspection?

 

[sstocker31]

Re: Odd clinking sound at WOT

You could try a better quality of gas, and see if that gets rid of the "clinking".....how old was the gas in it?
No need to tear it down, just don't run it WOT. If your only getting 3000 RPM (at WOT) it's most likely overproped. The engine needs to spin faster to prevent detonation under load. Try a smaller pitch prop.
When examining the plugs look for black specks on the white insulators....if you see this, those are tiny bits of piston....

 

[boatdiver2011]

Re: Odd clinking sound at WOT

The gas was only about 5 days old. I will check the prop, not 100% but I believe it is a 14.5" 19p 3 blade. What strikes me as odd- I have had this motor for years performing the way it does- except for the detonation- that is new. I would think if it is under propped, i would have had this trouble a long time ago.