slipping clutch?? 78 merc 20hp outboard

[fabguy5000]

Ok I know it is not a slipping clutch but that is what it feels like when I try to push the throttle up to higher rpm it feels like the clutch is slipping. The boat slows and the rpms go up as if it is a slipping clutch. The prop is tight on the hub I have already checked that. Also the thing has no reverse. The safety thing on the transome is broken but the reverse should still work if the little rod is held up or down you tell me. Maybe these two problems are related?? It just started slipping but the reverse hasnt worked in a while. Any help would be appreciated!! I can fix just about anything if I know where to look so hopefull someone can point me in the right direction. Thanks. Bob.

 

[Laddies]

Re: slipping clutch?? 78 merc 20hp outboard

That sounds like the prop hub is slipping

 

[fabguy5000]

Re: slipping clutch?? 78 merc 20hp outboard

Thanks for the reply!! I just checked the spline and nut and when I put it back on I tightened the nut by holding the prop still. Wouldn't this have made the hub slip while I was tightening the nut? Bob.

 

[Motor Boater Bill]

Re: slipping clutch?? 78 merc 20hp outboard

Mark the hub and prop, run it and see if they change.

One other thing--cavitation can seem a lot like a spun hub. Check the bottom of your lower unit and see if the nut on the bottom was over-tightened and broke the casing out there. This is a weak spot on the 20 hp LU. If so, you can fix this with some fiddling--an old socket cut down, a washer--keep the exhaust from exiting onto the prop. Been there, fixed that. By the way, of four 20 hp LU's I have worked on, three had the same broken place.

 

[fabguy5000]

Re: slipping clutch?? 78 merc 20hp outboard

Thanks for the reply! Which nut are you speaking of? It just started doing this reciently. And I have done nothing to the motor to change anything. Bob

 

[Motor Boater Bill]

Re: slipping clutch?? 78 merc 20hp outboard

There is a nut on the bottom of the LU above the prop, it's one of the nuts that holds the LU on. Check your prop hub first, but if it's good, then the problem could be exhaust in the prop slipstream from a hole in the LU. Remove the nut and look up in the recess where it sit to see if the casting above it is intact.

 

[Moisten Dailey]

Re: slipping clutch?? 78 merc 20hp outboard

I too have come across the same issue. I have a 1989 Merc 25 horse electric start with a tiller handle. I can troll at low speed but when I give it the throttle, the motor winds out but the boat won't go anywhere. Motor runs fine but it seems like a clutch slip if there is a clutch in there. I'm going to try your tips above and see if that helps. I'll let you know what I find and post back asap. Thanks.

I did notice that there is a rub mark on one side of the Prop's collar where it meets with the LU.

 

[Yepblaze]

Re: slipping clutch?? 78 merc 20hp outboard

Mark the hub and prop, run it and see if they change.

One other thing--cavitation can seem a lot like a spun hub. Check the bottom of your lower unit and see if the nut on the bottom was over-tightened and broke the casing out there. This is a weak spot on the 20 hp LU. If so, you can fix this with some fiddling--an old socket cut down, a washer--keep the exhaust from exiting onto the prop. Been there, fixed that. By the way, of four 20 hp LU's I have worked on, three had the same broken place.

I agree, as I too have chased this issue.

 

[Moisten Dailey]

Re: slipping clutch?? 78 merc 20hp outboard

I took off the nut and there is a coupling of sorts there. The half that is still in when I take the one off has a burr on one of the 3 large teeth. I'm not sure how that one comes off but will investigate more and update with some pictures if possible.

 

[Moisten Dailey]

Re: slipping clutch?? 78 merc 20hp outboard

I took off the large prop nut and removed the prop and there is a coupling of sorts there. The half that is still in when I take the one half off has a burr on one of the 3 large teeth. I'm not sure how that one comes off but will investigate more and update with some pictures if possible.

 

[fabguy5000]

Re: slipping clutch?? 78 merc 20hp outboard

You guys were right it was cavitation because the prop was not all the way on to the shaft and into the LU. That allowed exaust to get around the prop. I will fidddle with it more to make sure the nut area you spoke of is in good shape and that the prop fit is good around the LU. O.k. so now how bout the other problem I have with reverse. The aluminum piece that is supposed to hit on the transom tilt pin is broken and the safety rod for the reverse just flops around. I have no reverse. I really need a pic of what it is supposed to look like so I can look for a replacement. What is the aluminum piece called? Can I just wire the reverse rod up or down and make everything work?? Again any help is greatly appreciated!!! Bob.

 

[diaric]

Re: slipping clutch?? 78 merc 20hp outboard

sounds like your talking ablout the reverse lock, which should not affect it going into reverse. just engages clamps on tilt pin to hold motor down when in reverse. did your reverse gear quit after something like an impellor change on the water pump. i assume this is a tiller handle model?

 

[fabguy5000]

Re: slipping clutch?? 78 merc 20hp outboard

No it is not a tiller control it is remote. The water impellor was trash when I got the motor so I had to change it. The reverse has worked for me before but it is intermittent. I think you are right about my broken piece it probably was to grab the tilt pin in reverse. I didnt think about that. I am new to the boating world. The other day I had it out doing some fishing and had the motor tilted up while trolling with the electric. Then I tilted it down to head for the boat ramp and the thing would not go full speed or full rpm. I slowed and shifted into neutral then I tried reverse and it worked!! The motor tried to flip up (because of lack of the clamping mechanism) Then when I shifted back into forward it worked fine. Then when I got back to the boat ramp reverse was out again. Maybe a control problem???