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1999 Yamaha 40HP 40MLHX Clanking Noise at Low rpm idle / in gear?

T

tmetz

New member
Hey guys,

First off just want to say this forum is great, I use it a lot for my smaller Honda outboard quite often. But now I have one thing I'm stumped with!!


When I start my Yamaha outboard it has a very loud noise that sounds like the motor has a bad piston / crank letting loose or something of the sort it's pretty loud at start up only way to get rid of the sound is to raise the RPM's. It happens in forward, neutral and reverse.


I first heard the noise when I was out fishing with my wife, the boat just all of a sudden started doing it right as I went to start it up to move fishing spots. I would like to try and change it myself but from what I've been reading (self diagnosing lol) some say maybe a clutch dog or somewhere in my linkage that the noise could be coming from. No burning or grinding metal smells / smoke coming from the engine when cowling off and running on a hose. My compression checks out 110-112-110.

I pulled the lower unit off after running it just to double check everything was good and replace water pump while I was down there but have since left the lower unit off until I figure out what's going on. I was also having troubles with the cooling line last time I ran it the water would only come out in a steady stream if I held the muffs on the motor very tight, but when running WOT the water would still trickle out of the cooling line. Is there a way to clean my cooling system I'm wondering if maybe a decent piece of vegetation got wedged some where. I pulled my cooling line off to check for blockages and nothing of the sort.

Any help or ideas would be greatly appreciated!

Thanks, Tom!
 
Last edited:
Hi Tom

If you run the motor with the lower unit off does it still make this noise? When diagnosing problems I always start by trying to isolate parts of the system and help narrow down the cause. It could be a crankcase bearing, could even be the flywheel hitting something, could be something in your gear case. If you leave the motor switched off (lanyard out, spark plugs disconnected for safety) and put a socket on the flywheel nut then turn it slowly clockwise, do you feel or hear anything strange?

Stuart
 
Could be (amongst a lot of other things) a bad gudgeon pin/bearing. There is a simple test. Take out the spark plugs and put a long piece of dowel or similar down one of the plug holes. Rotate the engine by hand until the dowel shows that that cylinder is a TDC (top of the stroke). Rotate the flywheel another 3 or 4 degress past TDC then stop. Next push firmly on the dowel to see if the piston can be moved by the dowel. Do this for each cylinder by rotating each one just past TDC. On a good engine the piston will not move. On an older engine you might just detect a very tiny movement. ON a bad engine you will feel a definite movement and usually hear a 'click/clunk' type noise. This test gives a rough check of both the gudgeon and big end bearings. It isn't perfect, but is a quick way to check for what is a reasonably common problem.
 
aliboy said:
Could be (amongst a lot of other things) a bad gudgeon pin/bearing. There is a simple test. Take out the spark plugs and put a long piece of dowel or similar down one of the plug holes. Rotate the engine by hand until the dowel shows that that cylinder is a TDC (top of the stroke). Rotate the flywheel another 3 or 4 degress past TDC then stop. Next push firmly on the dowel to see if the piston can be moved by the dowel. Do this for each cylinder by rotating each one just past TDC. On a good engine the piston will not move. On an older engine you might just detect a very tiny movement. ON a bad engine you will feel a definite movement and usually hear a 'click/clunk' type noise. This test gives a rough check of both the gudgeon and big end bearings. It isn't perfect, but is a quick way to check for what is a reasonably common problem.
Click to expand...

Thank you guys for the quick response!! I do have the lower unit removed and found that I had a broken control bracket. I ordered a new one $44... That may have been some of the noise I had thought was the lower crank vibrating around in there. But after letting it run for 10-15 seconds the flywheel does have a rough motion to it I wondered if one of my magnets came off the inside of the flywheel or maybe I'm just over thinking this whole thing and it's just simply a new control arm that I needed. I took off the pull start cover and tried to get down into the flywheel to check it out but I do not have a fly wheel puller so I was a stand still. Motor runs great with lower unit not on, but still some off noise coming from the flywheel. I'm going to get a puller this week and try to get in there just for peace of mind I know everything is good to go for this motor. Is it possible I'm missing a couple magnets and my timing / spark is being thrown off?

I did not try the wood dowel trick yet, but I really do appreciate the input. As for now waiting on a couple parts for the motor and we'll see what happens!
 
tmetz said:
Thank you guys for the quick response!! I do have the lower unit removed and found that I had a broken control bracket. I ordered a new one $44... That may have been some of the noise I had thought was the lower crank vibrating around in there. But after letting it run for 10-15 seconds the flywheel does have a rough motion to it I wondered if one of my magnets came off the inside of the flywheel or maybe I'm just over thinking this whole thing and it's just simply a new control arm that I needed. I took off the pull start cover and tried to get down into the flywheel to check it out but I do not have a fly wheel puller so I was a stand still. Motor runs great with lower unit not on, but still some off noise coming from the flywheel. I'm going to get a puller this week and try to get in there just for peace of mind I know everything is good to go for this motor. Is it possible I'm missing a couple magnets and my timing / spark is being thrown off?

I did not try the wood dowel trick yet, but I really do appreciate the input. As for now waiting on a couple parts for the motor and we'll see what happens!
Click to expand...

I took the boat out for its first trip since putting in the new water pump and all and the noise is still there at a low idle rpm.? R

I I attached a video of the motor running
http://youtu.be/nVmtBPcKteYv
 
aliboy said:
Could be (amongst a lot of other things) a bad gudgeon pin/bearing. There is a simple test. Take out the spark plugs and put a long piece of dowel or similar down one of the plug holes. Rotate the engine by hand until the dowel shows that that cylinder is a TDC (top of the stroke). Rotate the flywheel another 3 or 4 degress past TDC then stop. Next push firmly on the dowel to see if the piston can be moved by the dowel. Do this for each cylinder by rotating each one just past TDC. On a good engine the piston will not move. On an older engine you might just detect a very tiny movement. ON a bad engine you will feel a definite movement and usually hear a 'click/clunk' type noise. This test gives a rough check of both the gudgeon and big end bearings. It isn't perfect, but is a quick way to check for what is a reasonably common problem.
Click to expand...


Can't thank you guys enough for all the little tricks to try, I just tried the dowel trick using a small piece of wood I cut down to make work. Just passed TDC I get zero movement on any of the cylinders all 3 remain in place and will not budge. After that i rotate engine with plugs out no wierd noises coming from internal of engine so far. Seems my bearings are okay with this easy test, it was very helpful!! Thank you!
 
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