A question for the mechanics

[KMR85]

I have an old johnson outboard (18 hp) from around 1978 or so. Was on the river recently and made it 500 yards from the landing and something happened to where the motor no longer goes into forward or reverse. It runs just fine while idling, but there is no forward or reverse. I thought maybe I sheared the pin that connects the prop to the drive shaft, but I didnt. If anyone has an idea what to check for I would appreciate it. I plan on looking at the motor this weekend. Thanks.

[mamohr686]

When you try to move the shift lever in and out of gear is it really hard to move? Have you ever had water in the lower unit? It could be the shift linkage or much worse ground or dammaged gears.

[KMR85]

No, the shift lever doesnt feel any different. When it used to shift into gear, you could really feel it. Now, nothing. I have not checked the lower unit for water though. When the problem ocurred, the motor was cruising and then it sounded like i gave it way more throttle though I was already going wide open. Then the current started me back toward the landing.

[marine_man]

Spin the prop by hand (with the motor off) and try and engage forward or reverse. Does it feel any different? Does it feel like you're doing anything by moving the shift lever?

marine_man

[iffy]

If it seems to shift easier now I'd say you lost a pin in the shift linkage. Check it all out closely. Possibly the bolt that holds the rods together in the midsection too. Pull the little plate off and look at it.

[Surface Tension]

Having this happen when cruising would lead me to believe the dog is worn. Before you go any further eliminate something simple.

You said you checked the shear pin but it wasn't the case. Did you pull the prop to determine this? You can shear a pin and have enough of a burr to think you didn't but it will slip under load. Next your prop nut, if not taken up all the slop will let prop slip back enough to where the pin is no longer seated in the prop. Normally that would happen in reverse unless you hit something.

There are two points on the shift linkage you should check. The point at the shift lever and then the link in the mid section. You'll have a rectangle plate with two screws between the power head and prop. Behind that is the shift rod and a link. That link has a set screw on the both ends that join the shift rod. Look to see that both ends of the shift rod are set in the link. Shift between gears and look for movement at that point.

[KMR85]

When i have the motor off and shift the motor into forward and reverse, the prop doesnt spin. In neutral it spins freely. I checked the pin by taking the prop off and looking at it. I will give your suggestions a try.

[marine_man]

It sort of sounds like your hub in the prop has spun then (but when this happens you don't usually notice it until you're above idle), that or the shear pin as Surface Tension suggested. What I would do is first check the shear pin, then I would watch your prop when the motor's in the water or you're running it on a hose - when you put it in gear what's happening? Is the prop turning, or the prop shaft just turning the hub inside the prop?

Take a magic marker (if you can see the line on the rubber anyway) or a white paint pen and draw a line between the hub and the edge of the prop where the hub is pressed into, run the motor and see if the lines are still lining up. If they don't the hub on your prop has spun and needs to be replaced or it's time to buy a new prop.

marine_man

[raymondk]

there only is a rubber bushing which dries out it is a very common thing in older johnsons I have seen 2 of them in the last 2 years.

[KMR85]

I checked out the lower unit more closely and there are no damaged gears, no problems with shear pin, shift linkage is all fine. So, I decided to take the boat out again and try running the motor. I can go in forward very slowly & reverse, good enough to troll a shad rap. When I increase the throttle past that speed, the propulsion stops yet it sounds as if you were running wide open. Motor starts and idles just fine. Is there a problem with the drive train? Anyone have suggestions or should i just bring it to the shop and get ripped off?

[marine_man]

Did you do this:

Quote:

---

Take a magic marker (if you can see the line on the rubber anyway) or a white paint pen and draw a line between the hub and the edge of the prop where the hub is pressed into, run the motor and see if the lines are still lining up. If they don't the hub on your prop has spun and needs to be replaced or it's time to buy a new prop.

---

It sounds like a spun hub to me

marine_man

[KMR85]

i will try that and see what happens, thanks.

[overdalimit]

Sounds like either it is cavitating or the prop is bad. Try a different prop.

[DigitalFisherman]

Just went through this with a 15hp mariner; you likely have a bad prop hub. You can ether have your prop rebuilt or buy a new one.

[KMR85]

i got a buddy with some extra props, so i will give that a try. it just doesnt look like anything is wrong with the prop.

[marine_man]

So the hub didn't slip?

If that's the case I would highly suspect it's something in the lower unit gearing.

marine_man

[KMR85]

I havent had time to check on the hub lately. I will either get to it today or tomorrow. I usually have things to do after work or I go fishing with others who have boats, so this whole situation isnt stressing me too much. thanks for your ideas and I will keep posting on progress. P.S. My old man thinks it could be the drive train, since the motor idles fine and can push the boat a little bit. Any thoughts?

[marine_man]

still sounds like it could be a slipped hub - they usually hold for a little bit and then slip continuously at highe rpm's...

At least, for your sake, I'm hoping it's a slipped hub. If it's not it could be big bucks...

marine_man

[KMR85]

thanks for all the info, i should get a look at it today.

[KMR85]

problem solved. tried my friends extra prop and the boat goes faster than before. thanks for the help with the spun hub everyone.

[marine_man]

glad you got it figured out!

marine_man

[KMR85]

actually you did!! thanks!