drive problem with old Johnson 20

[2stroke1971]

Ive got an old Johnson 20, a 1972.
It started jumping out of gear today for no apparent reason. In the past, if Ive hit bottom, or maybe run across some hidden lily pads at high tide its jumped out, so I know that its normal that if the prop gets obstructed that it will jump out.....but today, nothing was obstructing it.

One week ago was the last time out, we fish at least once a week, and NO trouble like this before today.

It was worse under more load...if you chugged slow, it wouldnt happen. If I held the selector lever forward, it would not pop out, but it would shudder every now and then and I could feel it in the selector handle...so I could force it NOT to pop out, but it was still trying.....

I am guessing that something in the drive unit is starting to bind up intermittantly...sound reasonable? What should I check?

Iv got NO experience with boat drive units, but Ive torn down and rebuilt many old motorcycles and cars, and I am a machinist, so no problems tearing into it, but what should I be looking for?

Could the oil be low in the gear case?
I was trying to find a diagram on the drive unit, but havent so far.....
Any suggestions would be greatly appreciated!

 

[tashasdaddy]

Re: drive problem with old Johnson 20

99% you have a bad clutch dog in the lower unit. diagrams here use dropdown menu to Johnson http://shop2.evinrude.com/ext/index.aspx?s1=bf6ad09c53cead335fcfd8a6471c0f7f

in the lower unit the clutch dog sides back and forth, to the forward and reverse geat. there are only 2 teeth on the gear, and very square edges. when they get worn, they will not hold in gear.

i have a 1974 25, that i just bought another lower, and took the guts out of it, and put in my motor. be careful, the bolts on the bottom of the lower unit, like to strip off, or break. heat helps.

 

[F_R]

Re: drive problem with old Johnson 20

Yep, worn out clutch dog and forward gear in lower unit. No doubt about it and very common. And no cure other than bite the bullet and fix it. All it takes is a little time and a lot of $$.

 

[2stroke1971]

Re: drive problem with old Johnson 20

SOUnds reasonable enough, I will check it out. Just dont know why it went from never happening to every 45 seconds ya know..seems to me that type of problem would have crept up on me...someone said something about the twist throttle and some linkage also....I guess I will drop the LU and check it out anyway, it should be apparent if its bad....
Cost of repair is a little scary...find another donor engine might be the way to go, if its something I cant fab up myself...

 

[2stroke1971]

Re: drive problem with old Johnson 20

Thanks for the links to the diagrams, very helpful.
If the gears are ok, it looks like the dog will run me about $106. I can deal with that. Couple hundred each for the gears>? Dont think Id do that, maybe look for another old motor, or borrow my Brother's to finish out the rock season. IT always happens this way doesnt it? 3 weeks later, and I would have been done for the season! AGRHHRHRH!!!

 

[rjezuit]

Re: drive problem with old Johnson 20

If you are a good machinist, with access to the right machine tools, you can square up the ears and ends of the gears slots so they will not slip out. Just be sure you get good engagement on the ears to the gear. Rick

 

[2stroke1971]

Re: drive problem with old Johnson 20

I got the lower half off pretty easily, all the bolts moved ok...

The dogs were a little beat up, of course, only on the sides that actually engage the gear...I had the bright idea of simply reversing the slider but the reverse side actually looked worse than the forward side. Yeah, I started to reshape the dogs; if they were just cubes, it would be a snap. These are loosely crescents, so duplicating the curve is crucial for engagement..then also Id have to make darn sure that both of the sides that actually engage were dead equal so they would both touch,,....
Rick...did you mean I should just MAKE them square? I hadnt thought of that actually....

The gears themselves were a LITTLE dinged on the outermost areas....again, a square hole would have been easier to clean up...
I had some other stupid finish-out-the-season ideas that I wont mention here, but I actually found the slider locally for pretty cheap. Got a line on a spare used unit as well...

The oil was milk white, and there was not much of it. I need to find out just how much is supposed to be in there, how to fill it properly, and check the level..anybody know this off hand?

My hope is that with a new slider with fresh dogs and new oil that it will hold, even with the gears being just a little boogered. Meanwhile I will get myself a spare set!

 

[rjezuit]

Re: drive problem with old Johnson 20

yes, just make them square. If you remove the same amount of material from both sides, they should engage correctly. They are machined tangent to the circle, so the cut is not square to the machine axis, unless you set it up that way. You can indicate the "unworn" area and then remove an equal amount from each ear to square them up. Some people have even done this successfully with a dremel, I would prefer a milling machine. The need is to remove a worn "ramp" on the faces causing it to cam out under load.Sort of like a worn phillips screwdriver camming out when you turn it. Rick

 

[2stroke1971]

Re: drive problem with old Johnson 20

Thanks for the advice everybody!
I got a shifter/cradle kit, it was an OMC set, "improved" no less. I installed it, filled it marine grade gear oil, and that did it!

Had her out Saturday night, and again all day on Sunday, didnt miss a beat!

Fish on!

 

[samo_ott]

Re: drive problem with old Johnson 20

You got and improved OMC shifter kit? where'd you get it? How much? did it include the gears? Probably not.

 

[2stroke1971]

Re: drive problem with old Johnson 20

No, no gears...got it from a marina in Annapolis. "Fairwinds" its called...$108. Not sure what the "improvement" was....larger contact area between the cradle and the slot was all I saw...

Anyway as an update, it jumped out on me once the third trip out....Im a bit nervous..the gears were not bad at all. Im gonna go over the shift arm linkage and make sure that the gear is tightly engaged when the arm is in the forward position...its got a lock bolt on the shaft and looks like you can adjust it....just to hedge my bets.