!999 Mercury175 EFI knock/rattle at idle /low rpm

[greenpiece]

Hello All.
I am new to posting here. I am wondering if anyone has had a similar issue?
My 1999 175 EFI v6 Outboard started to knock/ rattle at idle and low rpm, seems to be coming from the power head, this goes away at around 1200rpm. Other than the noise it runs fantastic. No loss in power. I have put over 150 (Hard) miles offshore since this started. (It should have blown up YES???) Could the noise be resonating thru Drive shaft? I have not pulled the lower unit yet. The motor has an extension, from 20 to 25inch my hope is,the little stub driveshaft is rattling around due to lack of grease on splines? Anyone have an opinion??
Thanks in advance

 

[Texasmark]

Mechanical noises can fool you as they travel through solid surfaces and can appear to be somewhere that they aren't. What prop are you running, pitch in particular. Changed it lately with a higher pitch or go from alum to SS? Is your gear ratio 1.87:1? When is the last time you changed or looked at your lower unit oil? If recently, what did it look like....any metal shavings (to speak of) on the magnet imbedded in the drain plug?

 

[greenpiece]

How the F does a flywheel come loose? did I destroy a shim or thrust washer?? I Hit it with an impact and now it purrs like a BIG CAT. Will it LAST??

Thanks for the reply TexasMark. I've Been an auto tech for years, and had sound do some FUNKY stuff. But This sounded Terminal, Like a hand grenade with the pin missing, but only at idle and leaving the Harbor.

 

[Texasmark]

Don't understand your first sentence. Did you indiscriminately just smack the flywheel with a hammer? If so, why? PO'd reaction?

 

[Silvertip]

Some merc engines have a bit of "prop rattle" as you come off throttle and while operating at low rpm. This should not happen in neutral at idle and may indeed travel up making you think it is a power head problem. If this is the issue it is an annoyance but not a problem that will hurt anything.

 

[Texasmark]

Some merc engines have a bit of "prop rattle" as you come off throttle and while operating at low rpm. This should not happen in neutral at idle and may indeed travel up making you think it is a power head problem. If this is the issue it is an annoyance but not a problem that will hurt anything.

That's where I was headed. But apparently he didn't have it always and wanted to see what he changed to cause it. The term is "clutch dog rattle" and is caused by the dog running up and down the sawtooth on the back of the F gear caused by irratic resistance on the prop shaft from irratic prop movements. I had it on the engine in my Avatar when I went from a 21P to a 24. I wanted the speed the 24 offered so I put up with the rattle. One way, especially when lining up on the trailer for recovery, was to do a lot of N to F switching. Also I think my 3 cylinder Looper was part of it too as it wasn't as smooth an idler as my previous Tower of Power.

 

[Shawnmm]

Nice work findind the fly wheel issue. I would loosen the nut again and retourqe it with a tourqe wrench. I'm sure the spec is easy to find, but could get it out of the book if you cant.

 

[greenpiece]

Thanks Shawnmm good advice. Sorry Texasmark for the poor English. I used my air powered impact Gun to tighten Flywheel. Took her out yesterday. ran strong as always, soooo quiet at idle and leaving the harbor. (took a 20# Yellowfin and a 40+ Bluefin, released two other BF) great day!!! Great motor!!
I wonder how many people have been sold a new engine due to this.