1971 Johnson 20 Horsepower engine Jump's out of Gear momentarly Ideas ?

[General Stuart]

Hello
I just picked up a nice looking Johnson 20 Horsepower engine that dates 1971 being model number 20 R 71S. The Prop. looks to have one fin bent a tad bit, so I am having that repaired. Mean while I placed it on my boat and took it on the lake to see how it ran. When I put it into Gear it seemed like a nice positive shift into the forward gear. As I gave it some throttle it seemed to Jump out of Gear Momentarly, then it resumed power if I backed out of the throttle letting it come back down to an idle. I did pull the Prop. before putting the boat in the lake and noticed a small Divit impression in the back of the Bronze bushing indicating to me that the round roll pin it meet's up to made this impression when they hit something solid with the Prop. When shifting the engine into Forward or reverse it seems very positive like the Linkage is fine not sloppy. In looking at the exteranal shift linkage I can not see any wear on it or looseness to it. The engine shows to have very little use as it is spotless inside the engine cover and does not even have the lower foot paint missing or looking worn and old. Can anyone tell me why it may be jumping out of Forward gear like this Momentarly ? Thanks in advance, General Stuart

 

[Cofe]

Re: 1971 Johnson 20 Horsepower engine Jump's out of Gear momentarly Ideas ?

If you are running it without a prop, the clutch dogs could disengage because there is not enough torque to hold them in place in gear. If you are revving your motor up without a prop, you risk having a run away motor that could self destruct. Never ever rev a two cycle motor up without any load on it.

 

[steelespike]

Re: 1971 Johnson 20 Horsepower engine Jump's out of Gear momentarly Ideas ?

The first thing that comes to mind is a worn clutch dog.Initially this will pop occasioanly at speed gradually becoming worse over time. There are also 2 dentent balls I believe in the dog that help maintain position these could be missing or worn.There is a Shift rod clamp inside a little cover on the leg the bolts go through grooves on the rods Not likely but could be assembled wrong.
The worn drive pin slot could indicate the motor has a lot more miles than indicated by the condition making a worn clutch dog more likely.Also if the idle was too high or the owner shifted
constantly at too high an rpm could cause premature clutch dog wear.

 

[General Stuart]

Re: 1971 Johnson 20 Horsepower engine Jump's out of Gear momentarly Ideas ?

The first thing that comes to mind is a worn clutch dog.Initially this will pop occasioanly at speed gradually becoming worse over time. There are also 2 dentent balls I believe in the dog that help maintain position these could be missing or worn.There is a Shift rod clamp inside a little cover on the leg the bolts go through grooves on the rods Not likely but could be assembled wrong.
The worn drive pin slot could indicate the motor has a lot more miles than indicated by the condition making a worn clutch dog more likely.Also if the idle was too high or the owner shifted
constantly at too high an rpm could cause premature clutch dog wear.

Hello steelespike
I am planning in taking the lower unit off this engine in the morning. Have you taken one apart to get down to this Clutch dog part ? Can you share with me what I have to do in taking the Lower unit off and apart to repair or see this clutch dog part ? Thanks in advance. General Stuart

 

[wilde1j]

Re: 1971 Johnson 20 Horsepower engine Jump's out of Gear momentarly Ideas ?

You will find an OEM shop manual very helpful here. Likely fwd gear and clutch dog. Good luck.

 

[General Stuart]

Re: 1971 Johnson 20 Horsepower engine Jump's out of Gear momentarly Ideas ?

You will find an OEM shop manual very helpful here. Likely fwd gear and clutch dog. Good luck.

Hello Jim & Other's
Well, I tackled this Job Without a Shop Manual. It was pretty straight forward in dropping the lower drive, I found out the engine shift Linkage had to be unbolted from behind the oval side plate area. Once I unscrewed the upper shift Linkage bolt, The complete lower assembly came off the engine. I Placed it in my bench vice and drained the gear lube, and removed the Prop. I Then took out the Six 1/4 X20 Bolts on the lower fin housing and saw I had to remove the Phillips head screw that holds the shift Cradle linkage in place. I was Very happy to see, there was No apparent Gear damage to the forward, reverse or Pinion Gears. I did find the shifter fork well worn that hooks onto the Clutch dog, but there was no metal filings or pieces in the case, so the good news is, I only need a shifter cradle assembly and new shift dog. I did however order a new lower drive seal set and new water pump with my other parts as I do not want to go through this work again. Thanks for those that helped, it really was not all that complicated, once I looked at it and figured how it was put together it is rather easy to work on. Regards, General Stuart

 

[wilde1j]

Re: 1971 Johnson 20 Horsepower engine Jump's out of Gear momentarly Ideas ?

If the clutch dog is bad, 95% chance fwd gear is also. Most people have never had a gear case apart and don't know how to ID a bad or a good one. Very slight rounding is enough to wreck a new clutch dog.

 

[General Stuart]

Re: 1971 Johnson 20 Horsepower engine Jump's out of Gear momentarly Ideas ?

If the clutch dog is bad, 95% chance fwd gear is also. Most people have never had a gear case apart and don't know how to ID a bad or a good one. Very slight rounding is enough to wreck a new clutch dog.

Hello Jim
After I took it apart, I took it with me to the Johnson Dealers to order the parts needed. Both the mechanic and I took the bottom half gear case off again as I placed it back on after seeing the damaged parts at my home to travel over to the dealership, not wanting to lose any parts or get dirt into it and he agreed, that all gears in my case were fine with nice clean straight cut edges not having been rounded off from wear, chipped or cracked, he felt all that I really needed was the shifter fork assembly, shift craddle, Clutch dog, seal kit and new water pump Impellor Kit to freshen the complete bottom gear case assembly...He further shared with me that he felt the shift fork in my engine may have been a bad design from that start and Johnson has now changed the parts status so you can only get the Fork & Carrier assembly together with a new clutch dog when ordering these parfts. :redface: I have an extensive back ground on working on race car engine's and their Transmission's from the past so this task was not all that hard for me... Regards