Strange noise from motor

[Gon Fishun]

Hey Chamelion, this is just a wild arsed assumption, (which we should never do) but with the very limited knowledge I have of outboard motors, could it be the flywheel - woodruff key flogged out and causing the flywheel to move ( rattle) and advance the ignition timing, as you say it picks up power higher in the rev range.
I haven't been able to hear your videos as I have been to slack to refit a video card to the PC and have no sound.
Cheers.

[Chamelion]

That's an interesting possibility and you're definitely the first person to mention it. Umm, I'll have to consult the workshop manual and find out what I'd need to do to get down deep enough to see it.

[Fed]

Hook your tinytach up & take it for a run, try it on each cylinder. At least that will rule ignition in or out.

When you did the 'bearing test' did you go past top dead centre, it would probably also help to put your thumb over the plug hole on the way down to create a vacuum which would pull up the slack better. I'd try that test again.

[Chamelion]

Hook your tinytach up & take it for a run, try it on each cylinder. At least that will rule ignition in or out.

When you did the 'bearing test' did you go past top dead centre, it would probably also help to put your thumb over the plug hole on the way down to create a vacuum which would pull up the slack better. I'd try that test again.

Haven't got the tach yet.. completely forgot about it actually. Didn't pay for it and never got a reminder.. will chase it up.

Tried putting a plug back in the hole for the TDS-1" lower movement as my thumb couldn't block it enough. Definitely zero play in the rod bearings.

[gazza2006au]

enough beating around the bush your either going to do something about it or not i see others have stopped replying for this reason

[Chamelion]

enough beating around the bush your either going to do something about it or not i see others have stopped replying for this reason

I am at a crossroad, granted.. Unfortunately I've been too sick to have a crack at it myself and I don't yet have the money set aside to pay someone to do it. So I'm going to continue gaining as many ideas as possible until such time as I have a solid choice in the matter.

I fully expect people to stop replying once they have no more to add... But understand, I am not intentionally "beating around the bush".

It IS very hard to know what to do when you're being told by 3 different current/past owners and a dealer that it's "normal", when it sure doesn't sound like it. lol

[WalrusLike]

Mate I am ignorant of all things mechanical, but I would say that after many years of observation I have found that following the advice of the missus is always a good idea.

Ensure your in Coastguard or VMR and enjoy the boat like she says.....

Worst case is a breakdown then deal with that... Best case is many years of happy boating.

[Chamelion]

Spent the weekend in hospital and only just felt well enough to have a fiddle with it today.. I feel I may have made some progress, so I'll share it here... If you're on the same page as the bloke a few posts up and you don't think I'm taking it seriously and just beating around the bush then by all means, I won't feel hurt if you stop reading now.

I spent hours reading through iboats searching for 'rattle' in every sub forum. It appears that my problem is definitely NOT unique. Plenty of posts there where the same symptoms, or extremely close to them, match to mine. Unfortunately in the many that matched very closely no one ever concluded their thread with the end result. Not a single person.. It was as if they gave up or found the problem and never bothered to share it.
Also interesting to note the OMC, Chrysler, Yamaha, Honda etc forums contained very very little, some of them nothing in 10 years of posts that matched my issues. So it very much appears to be a Mercury thing. In addition to that, most of the posts were from 25hp, 40hp, 50hp, 60hp and a couple of 115hp owners. The middle three being the same basic motor that mine is. Not to mention that all of them appeared to be in about the same age range as mine as well.. 1998-2004 the most represented.

Finally got a bucket big enough to cover up to the anti ventilation plate so I could replicate the sound at home and actually be able to walk around it rather than dangling half off the back of the boat like an idiot. I spent ages running it a bit above idle speed with a screw driver in hand listening at dozens of different points from just under the flywheel right down to just above the cav plate.

What I would like to say first is that none of the noise appeared to emanate from anywhere around the crankshaft area. It was all nice and 'quiet'. Top to bottom and the entire time I was listening to that area it was pretty clear the sound was coming from further toward the front of the motor. A few checks with the screw driver confirmed that the noise was loudest further toward the front of the motor and toward the bottom of the powerhead. Either at, directly behind or below the bottom carbie.
Just moving my head around the motor it was very noticeable, without the screwdriver, under the front of the powerhead, looking up from the mid section. Unfortunately there was no way for me to angle myself in there with the screw driver to have a listen.

I should definitely note that alongside the knocking sounds is definitely a little rough running. Engine shakes a little more and if i didn't know any better I'd say it felt like it was stuttering or suffering little backfires of some sort.

So that's that... I guess the big question is - What could cause a motor to make a knocking sound, whilst also possibly backfiring/stuttering and it only happens when there is pressure on the through hub exhaust? - Running too rich? Broken reed valve? I'm absolutely all ears. I certainly feel like I at least have some more useful information I can pass on to a mechanic should I find myself unable to continue diagnosing it myself.

I'll check my workshop manual to see how hard it is to pull the carbies off and inspect the reed valves.

In the meantime I need to consolidate my finances a bit and splash out on a good service with a water test and then go from there.

Thanks for listening

Matt.

[Gon Fishun]

Good read Matt. It will be very interesting to discover what the noise is. Don't stop now.

[astro66]

earings in the ashtray

[Chamelion]

earings in the ashtray

Hahahaha.. 'Problems' like that are always good for a laugh - A few years after you've gotten over how much stress you went through working it out.

[WalrusLike]

Mate I still think follow your missus advice.... ignore it.

Maybe that's why no resolution to all the threads.... everyone gave up and nothing came of it.

Remember though that I am ignorant....

I myself would get it serviced and if mechanic is happy then make sure your an associate VMR member and have a reliable radio then off ya go.

[Chamelion]

Maybe, maybe not.. Whilst I'm making 'some' progress I'm likely to keep at it. I think I'm finally getting somewhere.

A member on iboats suggested I might be getting water into the bottom cylinder via the exhaust baffle..... Now, I've just looked through the spark plug holes again and I've noticed something that I hadn't before. After last running the motor 6 hours ago the top 2 piston tops still appear moist and oily. The bottom one however looks dry. Still black like the others, but none of the moistness. So maybe there is some truth to his theory.. I'm not certain, I have some more reading to do.

[WalrusLike]

Chameleon you certainly deserve a win with this. I admire your persistence and hope it pays off for you.

I am following with interest... good luck with it.

[Chamelion]

Little update.. I'm using this primarily for my own records, but if anyone has anything to add, please, by all means do.

Ran some yamaha decarb through the motor this afternoon. Plenty of carbon got expelled into the water/atmosphere. Lots of white smoke and some black sludge in my flushing bin.
After the decarb she was idling a bit slower/rougher, so I unscrewed the lower carbs mixture screw a touch, which evened it out. The strange thing now is that where removing the bottom cyls plug before would result in really rough running, but removing either of the top two didn't appear to make any difference it's now the middle one that causes her to kick up a fuss. Removing the top or bottom doesn't appear to make much difference... Very odd.
At the very least there is definitely something wrong with the spark or fuel delivery/mixture. So I'll have to get that looked at also... I'm legitimately starting to wonder if the noise I've been hearing isn't just the motor pinging its arse off or the like.

Most definitely I am at the point where there is little else that I can do. So I'm going to see if I can find a reputable mobile mechanic to come out for a quick water test and have a listen.. See if he can check the spark and adjust the AFM a little to see if it helps.. Heck, maybe he'll have a proper stethoscope. The last bloke didn't, so we couldn't pinpoint the location of the noise.