SOLVED: 66 Johnson Seahorse 40HP - Worn Clutch Dog/ Violent "Misfires"

[Tin_Bubbles]

​EDIT: Changed title to help others find this topic/ help them with similar issues.

Back again. I've been fighting the motor for a long time now and I'd really like to get it on the water before fall hits.

1966 Johnson 40HP Super SeaHorse (RDS-28B).

She runs and purrs like a kitten in neutral, very responsive, no missing or anything. The problem lies when I get it into forward. After about a minute or two of running in gear, there is a fairly aggressive misfire and the engine shakes the boat. The misfires become more and more frequent as time goes on. They start about 45 seconds between each one, then become more frequent like 10-15 seconds between them. They scare me enough to take the boat right back to dock.

So far, I've rebuilt the carb, new spark plugs, gear oil, water pump/ impeller, gas is fresh, tank is clean, I rebuilt the fuel pump last week, checked the spark plug wires and they seem nice and flexible (no cracks or spots where they could short/ arch).

I'm running out of ideas. I talked to a mechanic friend who guessed that it sounded like an ignition problem. He suggested replacing the points and condenser. I am not familiar with either of those.

Does that sound right to anyone? I'm seeing the flywheel will have to come off in order to do that, I'm hoping that won't be a difficult job. Could the timing just be off? (The motor sat for 30 years before I got to it). I'll have just about every part replaced on this motor before I get it running solid probably haha.

Any input is much appreciated!

 

[racerone]

Well, ---It might be jumping out of gear !----But do this test.----Does spark jump a gap in air of 5/16", yes or no ?

 

[F_R]

That periodic jumping or banging at high speed is a classic symptom of jumping out of gear as racer just suggested. It is coming out of gear, rotating 1/2 revolution, and slamming back into gear. Until next time. Cause is a worn out clutch dog in lower unit, and usually a worn forward gear also. The longer you let it continue, the more damage is done. Eventually, it will beat the shift linkage to death.

 

[Tin_Bubbles]

That periodic jumping or banging at high speed is a classic symptom of jumping out of gear as racer just suggested. It is coming out of gear, rotating 1/2 revolution, and slamming back into gear. Until next time. Cause is a worn out clutch dog in lower unit, and usually a worn forward gear also. The longer you let it continue, the more damage is done. Eventually, it will beat the shift linkage to death.

Well, good thing I've dropped the lower about 6254 times, so I'll know how to get there. Is there any way to test with the lower off? What would some signs of a worn clutch dog look like?

You guys are awesome.

 

[Tin_Bubbles]

Also - instead of a worn clutch dog, could this be an issue of shifter height adjustment?

 

[lindy46]

Split the gearcase and remove the clutch dog. Check the "ears". I'll bet they're rounded/chipped on the drive surfaces. Same with the ears on the forward gear.

 

[F_R]

No Title

Also - instead of a worn clutch dog, could this be an issue of shifter height adjustment?

Wishful thinking. However as I said, it will be beaten to death if ignored. Then somebody will start "adjusting" it in an effort to stop the jumping.
Here is a severely worn clutch dog. They will start jumping long before getting this bad

 

[Tin_Bubbles]

Wishful thinking. However as I said, it will be beaten to death if ignored. Then somebody will start "adjusting" it in an effort to stop the jumping.
Here is a severely worn clutch dog. They will start jumping long before getting this bad

Excellent reference photo, thank you for that!

I will report back with some photos tomorrow

 

[Tin_Bubbles]

Well, you all were right. RIP clutch dog.

Crazy chipping on that. Here are the FWD and REV gears, starting with forward:

What do you guys think? Obviously the clutch dog is toast, but the gears don't look bad at all.

 

[racerone]

Make sure the adjustments are correct on re-assembly.----There is no adjustment on the lower unit or the brass shift connecter,.----But there is adjustment at the shift lever up top.----Make sure notches on shift rods line up with holes before installing screws in brass connecter.---By switching bushings the reverse can be used as forward gear.

 

[lindy46]

Gears don't look too bad. If it was me, I'd buy a new forward gear and clutch dog, and pick the best used gear for reverse.