terrible periodic clunk during cruise rpm

[ND]

Greetings folks.<br /><br />I have a 1960 Johnson 40 hp. Excellent, until now.<br />In neutral it is faultless.<br />In gear it idles perfect.<br />When I power it out a bit in forward, it starts to jump as though it goes out of gear and back in again. It almost rips the back of the boat off. It appears to be getting progressivly worse. The symptom is now occuring at lower and lower rpm.<br />What is it?<br />Thanks, ND.

 

[OBJ]

Re: terrible periodic clunk during cruise rpm

Morning ND....what's happening is your engine is jumpin out of gear. The dogs on the clutch dog and forward gear has worn so much that they pop out and back in. Does it feel like your hitting a log? For a rig this old it's not unusual. You will have to replace the clutch dog and forward gear. Few bucks but no big deal.<br /><br />OBJ

 

[ND]

Re: terrible periodic clunk during cruise rpm

Thanks for the reply OBJ. Correct me if I am wrong, but that stuff lives just behind the prop yes? Also, how do I take the prop off? The pin appears to be recessed into the prop itself. Do I have to attack it from behind or something?<br /><br />Thanks again,<br />ND

 

[Joe Reeves]

Re: terrible periodic clunk during cruise rpm

ND..... I'd suggest that you obtain a service manual for that engine first (bottom of this page). Guess work will just cost you money unnecessarily. The shear pin in the prop..... just knock it out. The OMC original and superceeded part numbers of the forward gear and shifter dog follow:<br /><br />Forward gear - 377174 = 381810 - approx $188.00<br /><br />Shifter Dog - 305105 - approx $47.00<br /><br />NOTE.... Although the teeth of the gears are perfect, it is the shift lobe contact area of the gears and dog that determine the quality of the parts. The lobe angles should have sharp right angle edges. The roundness of the edges is what causes the unit to jump out of gear.<br /><br />Both forward and Reverse gear are identical excepting the forward bushing. If the lobes on the reverse gear are perfect, you may transfer the bushing from the forward gear to the reverse gear.<br /><br />You may also reverse the shifter dog but keep in mind that you would be transfering the problem to the reverse gear.

 

[steelespike]

Re: terrible periodic clunk during cruise rpm

Just thought I would add :: After your rebuild be <br />sure to idle down fully before shifting and when shifting do it crisply dont drag it and dont jam it in.Your new parts wont wear prematurely<br /> with a little extra care.

 

[ND]

Re: terrible periodic clunk during cruise rpm

Is welding the dog and gears square again an option?<br />ND

 

[OBJ]

Re: terrible periodic clunk during cruise rpm

ND...my dad tried this once. Didn't last long. Also, the lobes must be exactly 180 degrees apart for correct engagement of gear lobes to clutch dog lobes.

 

[JRJ]

Re: terrible periodic clunk during cruise rpm

I took my 120 Johnson in with the same symtoms. I drained the lower end and found signs of water. The mechanic took the lower end completely apart and found nothing wrong other than seals. After test drive, I need a new fuel pump @ 291.50. After another test run,"sounds like a rod or rod bolt cap is going" and motor needs rebilt. I paid 1844.82 for parts and labor and parked the boat. You've got me wondering now...Thanks for the post and replies.

 

[papasage]

Re: terrible periodic clunk during cruise rpm

i had a 33 johnson that did the sam thing the shift rod under the power head was loose tighten it up ran it for several years it is still woreking . a friend of mine took his gears to a machine shop had them ground streight where the shift dog engages .it worked fine . those gears are expensive . if i had the prroblem i would check the shift rod for looseness . if the gears are warn it want cost much to have them cut back to 180. [ pull gears have a look .check shift rod for looseness] papasage