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Shifting Issues

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Nick Moore McCabe

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I have a 1986 40hp Yamaha on a boat I just purchased. Took it out today and am having some issues. There is a clicking/grinding sound when I put the engine in reverse, it does not seem to be engaging. I am thinking some sort of cable or linkage adjustment is needed. Forward engages fine, however, when I get to about 75% of full throttle, the engine starts to rev high and unloaded like something is slipping and the boat loses speed. If I back off the throttle, it will re-engage and act normal until I go past 75%. I have heard about a hub/prop issue being the cause of this. Does anyone have any advice on what is going on here. The motor has hardly been used and looks like it could be on the showroom floor. It runs perfectly so I am really hoping that I don't have to repower. Thanks in advance.
 
Sounds like you've spun the hub.
easy test, remove the prop and borrow one to sea trial.
if no issue, get your prop re -hubbed and you're golden.
 
dark_star said:
Sounds like you've spun the hub.
easy test, remove the prop and borrow one to sea trial.
if no issue, get your prop re -hubbed and you're golden.
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Thank you, that seems to be the consensus on the forward problem, but could that be causing the reverse issue too. Its a click/grind sound and hit or miss on actually engaging. I'm no expert but was thinking maybe the cable or linkage is out of whack and its not going "all the way" into gear. Any thoughts?
 
When shifting into reverse, you need to dump it in quick.
The quicker the shift the less grind you will hear.
mine does the same thing if you try and shift it slowly.
 
Nick Moore McCabe said:
Thank you, that seems to be the consensus on the forward problem, but could that be causing the reverse issue too. Its a click/grind sound and hit or miss on actually engaging. I'm no expert but was thinking maybe the cable or linkage is out of whack and its not going "all the way" into gear. Any thoughts?
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If a quick shift into reverse doesn't engage it all the time the shift linkage could be lose back at the engine or need adjustment. WIth the cowling off have someone shift from forward to reverse whoile you watch the shift linkage in engine. Only the linkage rod should be moving... if the plastic sleeve that houses the linkage is moving it has come lose from its anchor point. In there. If it hasn't come lose and forward always engages it may need adjusted to offer more travel into reverse gear (at the expense of some travel into forward gear). Somewhere in between is the happy middle that engages both forward and reverse gears without excessive travel of the linkage rod in one direction or the other.
 
deepsea21 said:
If a quick shift into reverse doesn't engage it all the time the shift linkage could be lose back at the engine or need adjustment. WIth the cowling off have someone shift from forward to reverse whoile you watch the shift linkage in engine. Only the linkage rod should be moving... if the plastic sleeve that houses the linkage is moving it has come lose from its anchor point. In there. If it hasn't come lose and forward always engages it may need adjusted to offer more travel into reverse gear (at the expense of some travel into forward gear). Somewhere in between is the happy middle that engages both forward and reverse gears without excessive travel of the linkage rod in one direction or the other.
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Awesome advice, gonna try this as soon as I get a chance! Thanks
 
Nick Moore McCabe said:
Awesome advice, gonna try this as soon as I get a chance! Thanks
Click to expand...

That's not to say you haven't spun a hub as well. What you reported in forward gear while underway when putting the throttle to it (loss of power matched with high revs at high throttle) is telling of a spun hub that tends to reveal itself under those conditions. I think you could have 2 probs going on at once... Spun hub as Darkstar mentioned and a gear linkage problem with your reverse gear engagement probs.
 
deepsea21 said:
That's not to say you haven't spun a hub as well. What you reported in forward gear while underway when putting the throttle to it (loss of power matched with high revs at high throttle) is telling of a spun hub that tends to reveal itself under those conditions. I think you could have 2 probs going on at once... Spun hub as Darkstar mentioned and a gear linkage problem with your reverse gear engagement probs.
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I agree 100%. I've been told to lock the flywheel and try to manually turn the prop to test it. Gonna do that and if it fails, pick up a new prop and hub. My main concern is ruling out major lower unit problems, hoping the shift cable is the culprit.
 
Nick Moore McCabe said:
I agree 100%. I've been told to lock the flywheel and try to manually turn the prop to test it. Gonna do that and if it fails, pick up a new prop and hub. My main concern is ruling out major lower unit problems, hoping the shift cable is the culprit.
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You can try that for the high throttle slippage and revs you are experiencing but unless you think you have the strength in your arms and hands that matches the torque and HP of your engine at high throttle I doubt you'll find a spun hub by trying to see if you can twist the prop by hand with the flywheel locked unless it has been spun to oblivion. Locking the flywheel and trying to twist the hub? Can you generate the kind of torque the engine is delivering at that throttle setting? If you can twist that prop by hand with the flywheel locked, you'd never have been able to get on plane.
 
deepsea21 said:
You can try that for the high throttle slippage and revs you are experiencing but unless you think you have the strength in your arms and hands that matches the torque and HP of your engine at high throttle I doubt you'll find a spun hub by trying to see if you can twist the prop by hand with the flywheel locked unless it has been spun to oblivion. Locking the flywheel and trying to twist the hub? Can you generate the kind of torque the engine is delivering at that throttle setting? If you can twist that prop by hand with the flywheel locked, you'd never have been able to get on plane.
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It's just a 40 horse, probably around 40 ft/lb of peak torque. It's not really much, the power lies in applying that torque at 5000 rpm, I just need an inch to know it's failing. Hell you may be right but I'm gonna give it a shot. If it doesnt slip, not gonna conclude it isn't failed. But maybe I'll get lucky and diagnose it without having to haul it to the lake.
 
Nick Moore McCabe said:
If it is a spun hub, is the prop shot or just replacing the hub itself will suffice?
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Inside the hub there are very think, big heavy rubber rings that reside between the hub and the outer prop that get seated and rammed in there with incredibly high pressure. They'll probably only need to replace those rubber rings. The idea of the rings is to absorb shock if the prop hits something and basically allow the inner hub to break lose from the outer prop thereby not delivering the shock of an impact to the gearcase and up into the crankshaft and everything else. From what I understand, sometimes they do their job and save vital components, sometimes they don't.
 
There's a shop nearby that has my prop with hub for $89 so I'm gonna go for that just to rule everything out. They were iffy about being able to rehub it and it jist doesn't seem worth the minor cost savings. Checked out the shift cable, super easy toolless adjustment, will know for sure if that was the issue once I can get it into the water. Thanks for all the advice guys, saved me a bundle I'm sure.
 
Do let us know how it turns out... Most of us here have learned the hard way so I know we all want to know what the outcome is and if your probs are fixed.
 
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