One 4 the experts!

[Neil]

I am posting this on behalf of a Friend.<br /><br />He has a 1994 Johnson 120.<br /><br />Problem is that the engine jerked when on the plane. He could feel a jerk (and what felt like a thud) Originally he thought it was flotsam but it was too regular. It used to happen once a minute but increased to 10 times s min. When these jerks used to happen he could look back and see the engine shake. He was not convinced it was a missfire as the engine didn't change pitch or sound.<br /><br />Our favourite mechanics suggested the gearbox was to blame. This was replaced with a second hand one. <br /><br />The problem dissapeared, but now it is back. Only once per min, but still there all the same.<br /><br />Any suggestions please. I suggested prop, but this has also been replaced with a second hand.<br /><br />Thanks<br /><br />NG

 

[Walker]

Re: One 4 the experts!

Sounds like gear box to me too. And with it starting to happen again with the new L/U I suspect improper shift linkage adjustment. The shift dog is not fully engaging and everytime it slips (jerks) it is rounding the dog edges causing it to slip even more.

 

[Neil]

Re: One 4 the experts!

Walker,<br /><br />Thanks for the response.<br /><br />Is this adjustment only necessary or affecting the switch from idle to forward/reverse?<br /><br />NG

 

[Neil]

Re: One 4 the experts!

Walker,<br /><br />I have been looking at an exploded view of a gearbox.<br /><br />I don't know where this shift dog is and how to adjest. I presume it must be outside of the gearbox if the symptoms are the same after swapping?<br /><br />Can you help me with the checking and setting please.<br /><br />Thanks<br /><br />NG

 

[Joe Reeves]

Re: One 4 the experts!

NGriff1.... The shift dog is an internal part of the lower unit. Adjust the shift cable as follows. As Walker states, this is due to having the shifter dog and the gear lobes rounded off. <br /><br />This rounding off of the lobes is due to one of two causes (or both). One is that the operator is shifting into gear slowly, thinking he/she is taking it easy on the shifting components. Actually this allows the sharp right edges of the lobes contact each other many times which rounds them off. The second cause is that the shift cable was not adjusted properly which of course prevents the unit from going completely into gear.<br /><br />Your lower unit is jumping out of gear, then being forced back into gear due to pressure being applied via the shift cable, giving the sensation of hitting something.<br /><br />Remove the shift cable at the engine from the shift linkage.<br /><br />Move the shift linkage of the engine by hand so that you can see the play that exists in the neutral position. Center that play.<br /><br />Grab the end of the shift cable and push/pull it to see what play exists in the neutral position. Center that play and install the cable to the shift linkage so that both line up properly and are centered.<br /><br />If the unit continues to jump out of, and back into gear, the lower unit will require repairing.

 

[Neil]

Re: One 4 the experts!

Joe,<br /><br />Brilliant!<br /><br />Thanks.<br /><br />NG