Strange noise from motor

[ericcs]

IMO, if it was a rod it would be rattling all the time, atleast when ever it's under load. would be handy to borrow another power pack to see if it's breaking down

[Chamelion]

That's what I'm hoping.. I've posted this same thread up on iboats, but haven't had any replies yet. Isn't that meant to be about the busiest boating forum on the planet?

I guess I might have to suck up the bill and get the local marine place to check it out.. But first, I might go buy another trim anode (mine disintegrated today) and will pick their brains a little whilst I am there.

[Spaniard_King]

Gearbox issue, posibly knocked a tooth off either fwd or reverse gear.

Pull the lower drain bung out and see what comes out with it.

[Owen]

Gearbox issue, posibly knocked a tooth off either fwd or reverse gear.

Pull the lower drain bung out and see what comes out with it.

I agree,
I've seen similar twice... Once on my own boat and once on a mates.
In both cases the tooth came adrift a long time after having struck something, so it wasn't the first thing to mind.

[Chamelion]

Drained the gearbox oil out a few days ago actually.. Couldn't see any chunks in the oil and I ran a magnet through the old oil for a couple of minutes (fairly strong magnet) and no shavings were present.

I'll have a closer look at the old oil in a minute.. It hasn't been discarded yet.

[gazza2006au]

That's what I'm hoping.. I've posted this same thread up on iboats, but haven't had any replies yet. Isn't that meant to be about the busiest boating forum on the planet?

they dont like to help aussies out on iboats ive found over the last 5 or so years ive been a member

pull your spark plugs out and turn the flywheel around by hand see if u can feel any binding and possibly listen for where the noise is coming from im thinking one of the flywheel magnets have come loose

[Chamelion]

Can spin the flywheel by hand no problem.. No noise when doing so. The noise ONLY occurs when there is pressure against the exhaust.

Sure has me stumped... this is my third boat and only my second one (cheap $1500 tinny, bought it on a 5 minute water test) has given me trouble free boating.

I just want to be able to enjoy owning a boat... after the issues I had with my first one you'd think I was well overdue for such a simple request.

[Fed]

One thing I thought I noticed in the video was when you took #2 plug lead off it made no difference to the motor running at all.
I still think it's misfiring.
When you pulled the plugs did you shake them into your hand and look for traces of water?
Have you pulled the plugs and peered inside the holes with a torch looking for any signs of water, washed piston?

[ericcs]

One thing I thought I noticed in the video was when you took #2 plug lead off it made no difference to the motor running at all.
I still think it's misfiring.
When you pulled the plugs did you shake them into your hand and look for traces of water?
Have you pulled the plugs and peered inside the holes with a torch looking for any signs of water, washed piston?

quote in red,,had the same problem years back (30hp evinrude), ended up being a leaking bottom crankcase seal. hard to pick at idle, but cylinder would drop off above that.

[Chamelion]

I don't recall there being any water on the plugs, but I'll double check that asap. Tops of pistons have an oily black residue on them, not washed.

Could misfiring alone cause the noises in the video?

[Fed]

If a plug isn't firing for whatever reason it can cause detonation which is the cylinder firing from compression & hot spots.
This can cause horrendous noises because the firing is uncontrolled and happening at the wrong time in the cycle.
I'm going by the noise I hear on my speakers, more of a clack than a clunk if you know what I mean. Having said that it may be nothing more than something in the pull start thingy going nuts but I don't think so.
Then there's the CDMs, I'm not even going to try to get my head around what goes on inside them.
Right now my best advice would be to get it diagnosed by a merc dealer and I wouldn't use it until then.

[Chamelion]

Sounds like its coming from somewhere down in the powerhead or just underneath it. Doesn't sound like anywhere near the flywheel and I couldn't pinpoint it with a screw driver or length of garden hose.

The engine will bang about like it is misfiring when it does it, she'll spit out more smoke and I can feel it with my hand resting on the intake baffle.

[Fed]

Take a look at page 1C-3 in your manual.

I suppose it wouldn't hurt to try it with a spark gap tester, I have never personally used one or even seen one but the yanks seem to swear by them.

I guess repco or supercheap have them, even a single and move it from plug to plug would do.

[Chamelion]

Well, bad news and more bad news... mechanic and I went through eliminating all of the simple stuff and everything we could diagnose from outside the motor. It's definitely coming from within the powerhead and preliminary educated guess points to the crank shaft and/or crankshaft bearings... No way to know without pulling it down and having a look.

Compression re-tested as OK. Timing is OK. Plugs are getting spark.

Best case scenario, I'm out hundreds, worst case I'm out thousands. Absolutely gutted beyond comprehension.

[gazza2006au]

could be a cheap rebuild if u have two piece conrods if u have one piece conrods its going to cost a fortune what model 40 merc do u have year and model number post this up and i'll tell u which crank u have