Yamaha 90hp TLRC 2 stroke Knocking

[Jim Hawkins]

My engine has a knock I first noticed while cruising. Putting an ear to the motor while idling I can hear it also. My research says it is very hard to know where it's coming from, lower unit or motor. The noise seems to run the length of the drive shaft. I realize it could be anything from a piston to the prop shaft so,

Question, if I pull the lower unit can I run the motor to see if the knock is still there or will it cause a problem?

 

[99yam40]

hook a water hose to the block if that motor has the flush connector available or hook a water hose to the up pipe heading to the power head when you drop the lower unit to keep the motor cool.
if you are just going to run it for a very short time, water may not be needed at all

 

[Jim Hawkins]

Thanks 99yam I'll do that but does that mean so long as I don't overheat the motor It won't mess anything up to run it with the bottom end UN-attached.?

 

[Sea Rider]

If it's a very short test time can run the engine with lower leg removed if assume issue is on powerhead, if for longer time runs connect water hose to lower tube as indicated or connect on dedicated powerhead flush port if having one.

Happy Boating

 

[99yam40]

Thanks 99yam I'll do that but does that mean so long as I don't overheat the motor It won't mess anything up to run it with the bottom end UN-attached.?

yes that is what it means.
biggest problem when not having water hooked up with lower unit on is melting the water pump. lower off that is not a worry,\ just over heating power head

 

[Jim Hawkins]

OK, good. I was concerned that there might be something that would come apart if there was no pressure from the driveshaft in the motor.

I'm thinking this is not a bad way to isolate the problem, better I guess than pulling the heads or prop shaft.

 

[robert graham]

My 1999 C90 Yamaha is a bit noisy as is common with 2 strokes.....Your noise may or may not represent any big problem....maybe get somebody with a very similar motor to listen and compare the sounds?......My wife and I were idling at the ramp one day and I was sure I heard some kind of rattling sound....she said, "you're being paranoid, let's go fishing!"...and we did and that's been 10 years ago or longer!

 

[Jim Hawkins]

Thanks Robert, but the problem got worse. It started not wanting to go into reverse and finally not at all. Removing the controls and attempting to shift manually did not work and the control cables worked fine. So I suppose down there in the nether regions I have something around the clutch dog sick or broken.

So next question, I'm considering opening up the lower unit to fix it myself. I assume I should replace seals at the very least while in there but besides maintenance what part would most likely be the culprit? Clutch dog, Pinion gear?

 

[robert graham]

Drain lower unit oil to inspect for condition/metal fragments that might indicate the problem. If your lower unit is in bad shape maybe search for a good used one to bolt on....might be cheaper than repair parts and labor....just a thought here...

 

[Jim Hawkins]

Thanks Robert, draining the oil was the first thing I did. There was no water and a few, what I consider normal, small flecks of metal on the magnet. Regardless, with controls off the unit will not go into reverse so something is wrong down there. A used lower unit would be $900 or more going by what is actually available and of course I can't know what I'm getting. I'd rather pay a little more to know the damaged part is replaced and new seals etc. Just have to find a honest mechanic.

 

[99yam40]

open it up and see what you find.
My brothers C60 had a twisted shift shaft, and a bent pin in the prop shaft /clutch dog.
someone must have tried to force the motor into reverse while the motor or prop shaft was not turning

 

[robert graham]

Over the years I've been guilty of shifting gears from forward to reverse and back with the motor off....found out that is a bad idea and can bend things in the lower unit....so I quit doing that. Maybe your unit was sometimes shifted with motor off and damaged that shifter mechanism. Getting the unit apart could be the biggest challenge.

 

[Jim Hawkins]

That's something I have done but rarely and when I do if it doesn't slide in smoothly I don't force it.

Well, I bought a new 4 stroke so this one will get put aside till I decide what to do with it. Probably sell it as a mechanics special.

Thanks for your input.

 

[99yam40]

So did you drop the lower and run it to see if it was just the lower unit?
knowing where the problem is means you can sell the good part for more money