1995 Merc 115 Engine Clatter

[gsepan]

When I throttle down I hear this knocking sound. It almost sounds like a a rod knock. The motor runs fine otherwise... Should I be concerned? Also I've never replaced my impeller and the stream of water coming from my motor seems good. Should I do this next season as part of preventative maintainance? And one last question to all you gearheads... What is the average life expectancy of an outboard if all you do is change the lower end lube every season, change the plugs and filter every 2 seasons? I've had 8 great seasons with my outboard and am hoping to get another 8 out of her with minimal repairs.

[wickedcarpenter]

take it in and have it looked at.$100 is better than having to buy a new powerhead insted of a rebuild.check the warter flush port above where the warter comes out and look for metal shavings, and check your lower unit for the same.Knowing what i know now,i'd take it in and tell them the problem.

[TONGA]

"sounds like a rod knock" you need to find out what that is!!!!!!
yes change the impeller!
as for the life expectancy of an outboard? I don't know,um, forever! ok so not forever but a very long time,,,8 more years should be no problem,,in fact I would expect 18 more years,,,youknow 2-strokes just seem to run forever!!
How long has your motor been making this noise?
I mean could it be just some spark knock from a bad tank of gas?

[sausageman]

If this is an outdrive it could be the prop rotating faster than the upper driveshaft on a sudden shut-down. The boats forward movement rotates the prop faster than the engine is rotating the driveshaft so a cog like gear at the shifting fork makes a knocking sound.
A simple test would be to shut the engine off while traveling in forward gear,,,,,just above trolling speed will do. If you hear the knocking sound it is the above,,,,if not,,,,better get it checked.

[Burksee]

You mentioned that you only here the noise when you throttle DOWN? (decell/slowing down) A rod or piston pin knock usually is most noticeable when a load is being applied (acceleration, throttling UP) Sounds like more of an ignition/timing issue. In anycase I'd get an "experts" opinion. I'm sure the price of having it checked out will be worth the piece of mind you'll get before it causes any "real" (expensive) damage.

[gsepan]

I think sausageman hit the nail on the head. It only happens when I throttle down real fast. I tested his theory about shutting down the motor at a slow speed and didn't hear a thing. Funny that I've never noticed that noise in the past though:confused: . Thanks to all who responded I'm a bit more at ease now. Tonga, I'll change the impeller b4 the start of next season as this one is winding down fast and I hate to pull the boat just b4 fall perch kickoff.

[Spanky]

Is it a "2 +2" ? My 96 115 is a 2 +2 and sometimes when its in the 12-16 hundred RPM range, the ignition has a bit of a hesitation. Just thought I'd throw it in there!

P.s. 2 +2 means, 2 cylinders cut out at low rpm to save fule and loading up problems. I love this feature.;)

[gsepan]

Yep.. 2 + 2... @ 1600rpm it kicks into 4 cylinder mode but mine tends to load up a bit when trolling at low "R's". Hey Spanky, Do you hear the same rattling sound as I discribed on the original post too? I'd feel more at ease if you hear the same sounds...

[ESOX]

I agree with Sausageman. My Merc 90 will do the same thing when the boat speed is higher than the engine speed. I don't hear it too often, because I usually throttle down and let her idle for a minute too cool down after a long hard run.

[Spanky]

sorry, mine doesn't make that noise. Don'r really have a load-up problem either. I hope you get it figured out.

[Auditor]

My 175 Merc bagan to make a lot a clatter at low speed down to idle shortly after I purchased it used. Talk about nervous. At mid to higher RPM's she sounded just fine.
I had a bunch of advice that all scared the Bejeessuus outta me.
I took it to a very good Merc mechanic who fixed it in short order.
Cost: under $100.00
for inspection, compression check, and.....TIGHTENED THE LOOSE FLYWHEEL.
Hope you fare as well. Now I just luv my "hot mama Merc". She can purr, and she can scrrrreeeaaammmmmm.