1970 Johnson 20HP...something is slipping under load.

[kawaboy-zx11]

i noticed the past couple times i went fishing that it seems like my prop is slipping under load (before i get on plane). it seems to only do it when its warmed up, like i go to my first fishing spot fine, then after that it starts slipping, the motor will rev high but boat does not move with it. i spun my prop last year so i put a new one on this year,(i also just changed the gear oil) i do not think that the prop is spun this time because i can pull the spark plug caps and turn the motor over by turning the prop, when i had the spun prop on there i could see the hub slipping before the motor could turn over. i tried adjusting my shift linkage to favor the forward gear this last time out but it did not help the problem. it DOES NOT make a noise like i hit something when it slips....it just all of a sudden winds up, then i let off the gas and grabs again till i try going fast again, is the only thing it could be is a worn clutch dog or forward gear? i want to rule everything out before i have to disassemble the lower unit. Thanks, Dennis

 

[Chinewalker]

Most likely the prop again. Mark the hub and prop nut with a sharpie marker and run the motor again.

 

[kawaboy-zx11]

ok, i already have then hub and the prop marked with a sharpie. will have to check it out next time i go out fishing. i will be kind of upset if it is the prop again, it was a brand new prop and i probably dont have 20 min run time on it. but i guess props are cheaper than gears. i will post up when i find out whether the new hub is spun again. Thanks, Dennis http://oi58.tinypic.com/2gxl47t.jpg

 

[kawaboy-zx11]

strangest thing, i put the prop back on and went fishing this evening, went wide open several times and it did not slip at all, i think i put the prop nut on tighter this time, in any case its working fine now and i am not going to mess with it again unless the problem comes back. Thanks, Dennis

 

[Sirrobin53]

May have been that the pin was not seated in the groove. Forward pushes prop against the pin.

 

[kawaboy-zx11]

well dang, this new prop was good for wide open the last 2 times out, till tonight on my way in it started slipping again. so i just checked it and sure enuff the hub is slipping i dont know what to do now, i just got this new prop and didnt hit anything, it was a new old stock prop probably from the 60-70's i wonder if the glue they use goes bad or something. im going to try to fix my old beat up prop, if i can press the hub out and glue it somehow i will fix this new one too. any ideas on how to keep the hub stationary? i have never worked on a spun hub. Thanks

 

[BigB9000]

Rubber probably get old.

Isnt there a way to re-hub a prop?

 

[F_R]

A prop shop can re-hub it. There is no "glue". The rubber is bonded to the brass hub as it is made. If that bond comes apart, it slips. BTW, trying to turn it by hand is not a test. Unless you are as strong as 20 horses.

 

[F_R]

No Title

Like this:

 

[60sboater]

A good prop shop should be able to completely rebuild and repaint the prop. I used to get it done on a 17x19 Mercruiser prop back in the 80s. It never slipped but the blades had minor damage and wear issues.