2006 175 Mercury Optimax - Rattling inside front of engine...

[n8cas]

2005 Ranger 185vx – Tournament Edition – Comanche Series
Mercury 175L OPTI serial number 1b424986 Sep 2006 Model 1175D73HY

It was running at normal speed / performance in the morning for a couple runs, but a slight but noticeable 'hunting' sound in the background that progressively got louder until mid-morning when I was moving from one spot on the lake to another it finally shut down on me while I was on plane at top speed. I could get it to start again but it wouldn't be able to stay on at idle, nevermind trying to put it in gear.

Took it to a guy I had worked with in the past, and we've figured out that there's some rattling in the front part of the engine. Fuel and Air pressure are good. When he took off the top part of the front (I don't know the name for this part, but it has the valve inside that opens and closes) it was covered with gunk - to the likes he had rarely seen. I've been using Mercury Optimax Synthetic Blend Oil since I bought the boat used in 2018.

We could hear the noise louder with this part off.

I haven't had any problems with this motor other than it guzzling oil pretty quickly in my opinion. Now, the engine won't run for too long on it's own at idle; it shuts off completely. Something in the front half of the engine is making noise (the back half seems fine). Could it be a broken rod or something? He's going to take the front apart and go in to take a look, but this is obviously a serious issue. Any thoughts? I'm going to have to make some serious decisions moving forward and I always like getting advice before someone like myself, who knows nothing about the internal workings of a complex motor, makes such a big decision. Thank you.

[JOE54]

yes very possible rod bearing failed or other possiblities too

[EuropeanAM]

Normally a compression test (or leakdown test), followed by removal of the entire Air Handler Assembly (for inspection) would be the "standard".

[n8cas]

Normally a compression test (or leakdown test), followed by removal of the entire Air Handler Assembly (for inspection) would be the "standard".

It was hooked up to his computer and each cylinder got tested (although the computer did not make it to 100% complete on the progress bar before it would shut down or the guy moved on to the next cylinder - it did 'rev' up on each cylinder though). I have a compression gauge, but have not done a compression test in a while. Pretty sure it's just remove the plug and screw in the attachment hose properly - start it up and get your reading.

I wish I knew a little bit more how things worked in the air handler assembly. I looked for some videos on YouTube, but only got videos on how the 2 stroke works without getting much information about how the air (with all the damn reeds) system factors in.

[EuropeanAM]

See the FAQ Section for the post "Compression Testing" (instructions included).

The BEST guide would be to invest in a Factory Repair Manual (hard/print copy- Mercury does not offer downloadable Service Manuals).

Be very careful about "tube" videos- many of them are riddled with costly errors.

[n8cas]

Pretty sure it was oil injection failure (or bearing failure) maybe even the broken reed piece (in photo) plugged the oil injection head for that cyclinder, There was oil in each except the middle one in the photo below where the bearings are melted.






Now I need to find a remanufactured 175 optimax somewhere because Mercury lists it as NLA. The cost of the new powerhead at 7714 is too high and not a smart move given my situation.

[JOE54]

ME-P6-29-R OBR parts 1 251 645 2050 call um , make sure your oil inj is working on all clys at repair

[n8cas]

Thanks. I called OBR, but it looks like the best move for me would be to send it to Chris Carson down in the Keys to get it fixed.

[JOE54]

agree