1978 Mercury 20HP prop/drive shaft issue

[jeffrey hamlin]

Hi Guys....

I have a 1978 Mercury 20HP outboard on a 14ft. boat and am having major issues with propulsion. The gears will engage and the propeller will spin when you put it in gear. However if you give the motor some throttle it will NOT push the boat forward. It is almost like you are in neutral. At low throttle, the engine will push the boat along at a very minimal idle speed. Anything higher than low throttle and the motor will not propel the boat. It just revs up real high and with no thrust.

I suspect the problem is the propeller or some missing parts on the drive shaft. I bought the motor used and had to get a propeller for it. I purchased a NEW propeller from Michigan Prop. With the order, I got (1) propeller (1) spacer and (1) prop nut kit.

When the new prop didn't do the trick, I took to some internet research. From what I can find, there should be a slew of parts on the shaft behind the propeller. Please take a look at this schematic:

http://www.crowleymarine.com/mercury...rts/481_17.cfm

The parts I currently have on my shaft are #72, #71, and #70. Other than that, I don't see parts #59 through #69 on my shaft. Could they be hidden inside the housing? I have not pulled apart the lower unit, I have only pulled off the prop. When I do that, I see a shaft...that is all. Having no idea what should be on the shaft, I am at a loss.

OK guys...I hope someone can help me with this issue. I want to take my son fishing, but obviously I need a working motor to make that happen.

Thanks,

JEFF

[Wingedwheel]

Jeff, when you say the prop spins is this out of water with no load? what you're describing is a classic case of a spun hub however with a new prop that's very doubtful. When you put the engine into gear is there a noticeable "clunk"? Also what does it do when you put it in reverse?

[Ldavidgrover]

# 59 you wont see unless you take the bearing carrier out. #69 is you thrust washer. IT should be on there. It might be stuck on the prop shaft or came off on the back of the prop. Is your motor a tiller or remote?

[jeffrey hamlin]

Thanks Guys.

There is a "clunk" when you put it in gear. I took the boat for an hour drive up the river today, so I know the prop and gears are engaging. It was just a VERY SLOW trip as I could not do anything more than idle speed.

Oddly enough...reverse seems to have a very good bite to it. I mean, when I put it in reverse, I can really feel the thrust and I can give the engine gas and it will actually accelerate. Could I possibly have a spun hub?

Oh yeah...It is a tiller.

THX!

[carholme]

Jeff;

Shift into Fwd gear and gently (that is don't keep turning when you feel resistance) turn the prop CCW and tell us what you get, then turn it CW and tell us what you get.

Repeat this for Neutral and Reverse and let us know.

What is your engine s/n?

Gerry

[jeffrey hamlin]

The serial number is 5083919

When the motor is OFF and I put it into Forward Gear, I can turn the prop by hand. It will turn freely for a bit and then it reaches a point where it feels like it catches, but only slightly so....after this I can easily keep turning and then it catches again....turns easily catches, etc.

In Reverse Gear, I can only turn the prop a little bit and then it will not turn any more.

I hope this helps.

Thanks guys for taking the time to help a newbie out.

JEFF

[carholme]

Jeff;

Trying to help here so please try it again and as the previous post asked:

Forward: CCW Turn yes/no CW Turn yes/no
Neutral: CCW Turn yes/no CW Turn yes/no
Reverse: CCW Turn yes/no CW Turn yes/no

Parts listing for your engine:

http://www.crowleymarine.com/mercury-outboard/481.cfm

Service Manual P/N: 90-75512

http://www.chrysleroutboards.com/mor...ce_manuals.htm

Gerry

[jeffrey hamlin]

Forward Gear-
CW: Prop will turn freely, hit a point, then will keep turning freely, hit a point, then will keep turning freely
CCW: Prop will NOT turn

Neutral-
CW, CCW: Prop will turn freely in both directions

Reverse Gear-
CW: Prop will turn a slight bit and then it stops
CCW: Prop will turn a slight bit and then it stops

Gerry....what year did you find that serial number to be? Was it a 1978?

Thanks,

JEFF

[i-flier63]

Sounds like the clutch dog is wore out (refered to as clutch assembly in the skematic) or the shift linkage needs adjusted.

[i-flier63]

item # 55 in skematic ( clutch dog )

[carholme]

Jeff;

Sorry to abandon you but got called away.

Yes, it is a 1978 engine. In Forward gear as you described above, turning CW each time it hits a point, does it sound like a ratchet. If so, the gearbox sounds like it is operating normally.

Just to rule out the spun hub, you can put a witness mark across the hub and take it for a short trip and rev the engine up a few times, then check the witness mark to see if the hub has spun.

I'll be back later, I am trying to find an online manual for it.

Forgot to ask, is this a tiller or remote setup?

Gerry

[jeffrey hamlin]

Hey Gerry...

Thanks for your help. At this point, I am gonna return the prop to the marina I bought it at and get a new one. My dad concurs that it sounds like a spun hub.

Thanks!

[Wingedwheel]

So what did you find out about the prop?

[Mastapaine]

I am having the same problem with my 1978 mercury 200 20hp. My mechanic seems to think i need more pitch on the prop. Is the hub an easy fix?

[Wingedwheel]

Mastapaine, you would have to get a different prop to change the pitch. Why did he say that?

[Mastapaine]

Mastapaine, you would have to get a different prop to change the pitch. Why did he say that?

Well personally i think the hub is spun, but i told him about moving so slowly he said i probably needed pitch.

[jeffrey hamlin]

Hey Guys....

To conclude this thread, it was indeed a SPUN HUB. Sorry it took so long for me to post the findings. I exchanged my "new" prop for a newer prop and it works like a charm. Thanks to everyone who offered up advice.

JEFF