Johnson TD-20

[Evinrude 25]

Hello,

After picking up 7 motors, I have a good project for long time. Here is the list. 1939 Neptune was seized, I soak the cylinder head now. 1946 martin 60 outboard was seized.

1945 Johnson TD-20 5hp Outboard Motor. 1948 Johnson TD-20 5hp Outboard Motor. 1951 Johnson TN-27 5hp Outboard Motor. 1957 Johnson FD-11  18 hp. 195x Johnson 10 hp.

I am currently working on 1946 Johnson TD-20 first. After unseized it and cleaned up the points, it got a blue spark. Compression on top cylinder is  60 psi and bottom cylinder 68 psi. Is this number still good for this motor? I plan to clean the carb next step and see if it could run. This is my first project with pre-1950’s motor so I am learning now.

Other question is if I could not unseized the Neptune, I will have to tear it apart and clean up all parts. Just want to know if gaskets or parts available to put it back.

 

[Buccaneer]

If the compression was 68 on both cylinders, then it would be a decent
“idler”. Between the “spread” in compression of 8 psi, and 60 psi
on the lower cylinder, it will run, but may not idle good.
Could a ring be stuck on the 60 psi cylinder?
If lucky, it could unstick itself after running it a few times.

I’m guessing you’d have to make new gaskets for the Neptune,
but a good thing to learn if you like old outboards.

Prepare to be boarded!

[lloyd]

Really good compression for TD’s and TN’s is about 75 psi, but they will idle OK down to about 70 psi. Your rings are probably just stuck.  They run on 16/1 gas oil mix so the rings rarely wear out. Instead the primer seals wear out long before the rings wear out and that is what puts them out of use. Lots of good info at  pochefamily.org/outboard.  But note that the ad there for my new primer seals and installation instructions is about 15 years old. I had to raise the price to $10.00 about 5 years ago as it’s getting harder to find the proper leather to make more.

1 user thanked author for this post.

Evinrude 25

[frankr]

I had one that ran at 60 but wouldn’t idle. They are a good history lesson with 3rd port engine and rotary valve and the unusual carburetor if you want to get into it

[Evinrude 25]

I ‘d like to keep learning and keep updating with this good history lesson!

[Evinrude 25]

Just happily to report back that it is running without cleaning up the carb.

I ran it for 20 min and it was idling nice but after that the compression was still 60 psi for the top cylinder. I had added the seafoam on the gas to loose the ring.

https://www.youtube.com/shorts/racpUlbGhLk

 

 

 

 

 

[Buccaneer]

Sounds great….. you did good!

Prepare to be boarded!

[Author]

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