2002 40hp Mercury 2 stroke knocking noise

[Chamelion]

Re: 2002 40hp Mercury 2 stroke knocking noise

Appears it may be the cam shaft ball bearing (lower).. Can't be sure without pulling the engine apart, but the mechanic and I pretty much covered everything else. I'm keen to seek more opinions before I give the go ahead to get the powerhead pulled apart because I'm sure that the labour in doing that alone is going to set me back hundreds and thats a lot to lose if it's unlikely to be the cause.

Does it sound like it's the likely culprit to you fine folks?

 

[Maxz695]

Re: 2002 40hp Mercury 2 stroke knocking noise

View attachment 171255View attachment 171254View attachment 171252View attachment 171253If the lower crank bearing has been making this noise for a long time then it,s due to lack of lube through the oil fitting to oil it, and, or water intrusion throught the lower seal. If thats all it is and the crank, and connecting rods, rod bearings, and the wrist pin, as well as there bearings check ok then I would get a manual, get a powerhead gasket set or at least the exhaust plate gasket , By an oldstock new bearing off ebay usually about $20. Much more expensive eleswhere. Get the lower seals and the O ring for the end cap, and take it down replace the bearings the seals (2) usually per lower end cap. clean out the brass oil fittings, change the oil hose if cracked, and put it back together. It does as I suspect appear to be the lower bearing from what I can here. I think if it where the rod bearings it would be doing it more frequently. This is a job you could do your self. You seem machanically inclined enough to get it done. The lower end cap can be removed with a puller without loosening the intake. The bearing may be able to be removed then Not sure if you can get a puller in there. The powerhead in any case will have to be removed. I would disassemble the intake anyway to inspect the rest of the componants inside as if there was water intrusion I think your gonna find alot more that needs fixing at that point. I posted a set of 3 cylinder cranks, One with a blown journal. as you can see what worn bearings can do, and the bottom of my 3 cyl 70 HP should be close or the same to give you an idea what to look at. I ncluded a picture or a 40 HP intake manifold just for reference perposes. I put in the 2 cyl 40 crank picture so you can get a better view of the bearings

 

[Chamelion]

Re: 2002 40hp Mercury 2 stroke knocking noise

Thanks a lot for that.

I've recently been contacted by someone who has owned an identical motor to mine since new. He says that his has always made that noise and when he had it checked out at the 20hour mark there was nothing alarming found to be wrong. He's put a lot of hours on it over the last 10 years and apparently it hasn't become any worse.

I also spoke to my local mercury dealer and he was quite adamant that he had heard the same noise and known of the same exact symptoms many times in the past... I would love to put into words how he explained it to me, but I'd probably relay it incorrectly and just cause more confusion.. However, I will say a few key words - Something to do with how the engine cuts spark to avoid over revving and it's related to something at the top of the powerhead. He also explained it as a type of harmonic 'resonance' (sorry, I can't recall the actual word he used).

Having ruled out rod bearings, top cam shaft bearing, timing and a host of other possibilities my options have boiled down to a) Having the powerhead stripped down for diagnosis, which could be an expensive waste of time if what I've discovered leads to be correct or b) running it as-is for the time being and keeping a very close ear out for change in the noise. If it worsens I'll get onto it promptly - Though I know by that point it's possible it'll be already too late. A calculated risk.

I'm off for a fishing comp over the next few days. I'll see how it goes and when I get back I might look at contacting some more marine mechanics for their input on the matter, especially those who regularly deal with/in Mercury outboards.

What I am absolutely certain of is that in the literally DOZENS of hours I've put into researching this problem I've only found two video clips with the same sound, which both turned out to be a problem between the flo torq 2 hub and the particular prop they were using and I've found only ONE person with the same motor who has the exact same symptoms and his has run fine for a decade.

If I had the money to spare I'd just get it torn down to be sure, but I don't. So I'll investigate some more, keep a close ear out and MAYBE I'll consider tearing it down myself and doing whatever work is required as I find it. I feel confident enough to get it right providing I take my time.. A hard ask over summer!

Thanks again

Matt.

 

[Maxz695]

Re: 2002 40hp Mercury 2 stroke knocking noise

good luck Even if it is just the lower bearing it is just gonna make noise then more noise until something gives. If it does then you will have other problems as a result of the bearing giving in. Go easy good luck. The oil ports to lube the bearings on my block and intake where solid crap in there I got them free with a drill bit and a nail. Free flowing oil to my new bearings is a good feeling

 

[ScottySt]

Re: 2002 40hp Mercury 2 stroke knocking noise

I have a 2004 Mercury 25hp 2 stroke bought it about two months ago and yesterday it started making that same rapping noise as your youtube video i was running almost wide open and it just started to idle down almost the same as if i was just slowing it down then the rap started so i ideled it back to the trailer. I'm taking it to the Merc dealer tommorrow morning not looking forwrd to the bill but i have to have it fixed ill let you know how i make out. Still sounds like something loose to me but im not that lucky. Very weird noise not steady with the piston stroke very irratic .

 

[Chamelion]

Re: 2002 40hp Mercury 2 stroke knocking noise

I have a 2004 Mercury 25hp 2 stroke bought it about two months ago and yesterday it started making that same rapping noise as your youtube video i was running almost wide open and it just started to idle down almost the same as if i was just slowing it down then the rap started so i ideled it back to the trailer. I'm taking it to the Merc dealer tommorrow morning not looking forwrd to the bill but i have to have it fixed ill let you know how i make out. Still sounds like something loose to me but im not that lucky. Very weird noise not steady with the piston stroke very irratic .

Yep, sounds the same.. Very interested to hear how you go, so please do let me know what the diagnosis is.

I've put another 10-15 hours on mine since my last post and it's still running.. Still very undecided on what to do.

 

[Chamelion]

Re: 2002 40hp Mercury 2 stroke knocking noise

http://www.youtube.com/watch?v=-1wLFkIxI24

This one appears like it might be making the same noise.. You can hear it around the 2:13 mark when they briefly slow down. hmmm.

 

[Chamelion]

Re: 2002 40hp Mercury 2 stroke knocking noise

Someone commented on my youtube clip stating it sounds like the lower end bearings.. I assume he means the bearings within the gearbox.

Is it possible for this to explain all of the symptoms including the fact it only happens with the lower unit in the water and not on muffs? Is it possible for the sound to travel so much that it sounds like it's in the powerhead when it's not?

On another tangent.. Wouldn't just be the pull start teeth chattering against the flywheel or something, would it?

New video whilst I am at it: http://www.youtube.com/watch?v=iNl3ofJwqqY

Unfortunately as of this moment I'm still trying to narrow down the causes before I try to pull apart the motor myself or pay someone to do it. One of my bigger concerns is that it appears the powerhead bolts under the lower cowling are very rusted.. I hope they don't break off when attempting to undo.

 

[Chamelion]

Re: 2002 40hp Mercury 2 stroke knocking noise

If it really is a cam bearing I assume I'll need a complete rebuild? If that's the case, I assume it would cost upward of 2.5k?.. I may as well sell this one as-is and look at taking out a loan and buying a brand new Tohatsu 3cyl 40hp for $4250~. Real bugger with that is my $5800 boat turns into $10000 and resale would still be around the $7500 mark even with the 'new' motor ... I'd love to get it looked at, but I'm guessing I would have to be up for $500+ just to have it pulled down, checked and put back together. Quite a risk in the hope that I could get away with just replacing the bearing.

I could pull it down myself.. But I would have to buy certain tools to make it happen. Flywheel puller and torque wrench at the minimum.

I really don't know what to do... Very very confused.

 

[Maxz695]

Re: 2002 40hp Mercury 2 stroke knocking noise

I explained on another post waht to do in the situation where the bolts are rusted or rounded pertaining to the powerhead studs. Get a thin wood chisel and hammer make a dig in the nut just off center deep enough to grab and secure the chisel. Then give a couple of sturdy hits at the chisel with the hammer but not to hard as to break away the meat of the nut. It should be enough force to losen the nut. Make sure you soak the nuts several times with penetrating oil. Even over a few days if nessecary. After the nut gives repeat on the next section of the nut until you have Digs in it all the way around losening the nut (Counter clockwise) until the nut is off. I have had to do this on 2 motors and it worked on every single nut. Do not make the dig to close to the edge of the nut. The more meat you have the better your chances of having success

 

[Chamelion]

Re: 2002 40hp Mercury 2 stroke knocking noise

Cheers I've copied that over to a text document for future reference.

Matt.

 

[Chamelion]

Re: 2002 40hp Mercury 2 stroke knocking noise

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.

 

[Maxz695]

Re: 2002 40hp Mercury 2 stroke knocking noise

To me the shuttering and the fact that it (The Knocking) is appearently in the lowest sector of the enginge would indicate water intrusion through the exhaust port baffle and ito the lowest cylinder that may have been occurring for some time un noticed. The rods wear the needle bearings wear from lack of proper lubrication and the cranckshaft will also be affected possibly to the point of being unusabe and would have to be replaced. This is just My guess and you should do further investigation into the situation before dismanteling the exhaust cover to inspect the piston for sings of water damage through the piston exhaust port. This may or may not be that difinitive and appearent and further dismantel of the powerhead and the intake manifold will have to be done to inspect the play of the connecting rods side to side pressure will indicate the amount of wear or play. There should be some bit minimal amout about 1/16th. If the rod bearings are shot chances are the wrist pin bearings are as well. A new wrist pin and bearings can be installed. A bit tricky but not hard to do. The piston should be checked at that point for scuffing and scoring to see if it,s reusable. Check the compression before removal to give you an indication of the rings condition to see if there reusable.also check the cylinder walls and with any luck it will be ok or need a slight honing to freshen her up. I used to have a picture of my lowest crankshaft journal that was wiped due to water intrusion. I still have the crank and water damaged piston out back out back and may post a picture later on today if i have time. I will include a picture of my block with the replaced piston and rods to give you an idea of what to look for and what you will be getting into if you have to go this route. I cross hatched the cylinders and i,m waiting on 3 new rings for the bottom piston at this point. Is you 40 HP 2 cyl or 3?

 

[Chamelion]

Re: 2002 40hp Mercury 2 stroke knocking noise

Could that also be why it appears there is steam coming from the exhaust on top of the mid section for a little bit after engine shut down? - Have noticed this before, but didn't think to mention it.

If it makes any difference, the bottom plug does not look any different to the middle and top. ie: Not cleaned. The piston crown is also the same darker colour as the middle and top.

I guess, closer to the point.. How does water get into there in the first place and why would it only be noticeable whilst in the water and not on muffs?

I'm grateful for the reply, thank you very much.. Just trying to wrap my head around it.

 

[Maxz695]

Re: 2002 40hp Mercury 2 stroke knocking noise

View attachment 173678View attachment 173679 2 cylinder and 3 cylinder crankshaft with the end bearings on them in pictures for reference View attachment 173677 This is a 70 HP 3 cylinder exhaust port you can see the bottom portion is discolored indicating water intrusion past the divider plate and then into the ports where the cylinder rings can be seen and the piston can be observed. Hot gasses leaking out cause steam and overheating. At the same time water enters into your engine reaking havoke on the internal componants. Your knocking is indication there may have been sugnificant damage at this point and will only get worse if not addressed. If your very very lucky only the lower crankshaft bearing that goes into the lower endcap will have to be replaced without damage to the other componants I have described as possibly affected(edit) your compression numbers looked ok from the first post. Your plugs not being steam cleaned is a good sign. Hopefully it hasn,t been run alot with water intrusion and may have only affected the lowest crank bearing that could be making the noise.

 

[Chamelion]

Re: 2002 40hp Mercury 2 stroke knocking noise

Just looking through the spark plug holes again I've noticed something I hadn't before... I last ran the motor about 6 hours ago. The top of the pistons on top and middle both still look quite moist and oily. The bottom one whilst still dark in colour looks very dry. Definitely doesn't have the moistness of the other two.

Sounds like we're making some progress.. Does this sit well within your theory? - It's starting to look very bad, but it'll be nice to know what's wrong regardless.

 

[Maxz695]

Re: 2002 40hp Mercury 2 stroke knocking noise

Could be the rings or pitted piston is not pulling fuel or at least having enough suction to fully open the reeds in the bottom cylinder. This cylinder would be the the one affected due to water getting into the block but swap plugs wires plugs and see if it changes to be sure niether of those parts is causing the issue there. I frequently edit posts so be aware that I add change or correct info from time to time. You should after swaping the plug and wire on #3 remove the lower carburetor and clean it check the float level, make sure it,s not sticking and the needle seat are sealing properly. The bulb should get hard when pumped up if not there is an issue with the carb. You could also like I did when having a problem with my lower carb swap it with the upper carb but you will have to swap the spings as the lower one is lighter gauge than the upper one and you will have to swap the throttle levers as well. These steps won,t fix the knocking issue but it may help determine if the cylinders are all firing correctly. Be sure to remove the fuel line fittings on the carbs and blow them out real good as sometimes fuel line particals get in there anf block fuel flow. Do a visual inspection inside the manifold on the reeds and see if any are broken or bent. A reed that is not closing all the way will definitly affect intake of fuel.

 

[ScottySt]

Re: 2002 40hp Mercury 2 stroke knocking noise

Me again had the lower end bearings (gearbox)replaced, new pinion, had to even replace forward drive gear teeth were mangled so replaced those as well and good news (not on my wallet) but motor is good as new no knocking or rattling everything is back to normal. My rattle sounded from up top as well (sound travells) it is exactly the same as yr first youtube vid

 

[Chamelion]

Re: 2002 40hp Mercury 2 stroke knocking noise

Thanks mate, I appreciate the follow up. - Did you get to view my second video? It's far better at highlighting the sound.. compares to that one?

I just wish I could find the link between/the reason why mine will only occur whilst in the water and not on muffs. That part is very baffling.

Being that the previous owner broke the skeg there is no doubt something was hit at speed, so it is entirely possible there is damage in the lower unit and it is entirely possible that any metal shards were removed by them during a previous change.

I think I'll have to get a bearing puller and inspect the LU.

 

[Chamelion]

Re: 2002 40hp Mercury 2 stroke knocking noise

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.