Reply To: Compression for 58 Johnson 10 hp?

[Phil Budne]

OMC never published numbers for compression. I have a 1960 Johnson (all of this applies equally to Evinrude/Johnson 10hp engines of the 50’s and 60’s).  1958 is my favorite year for Johnson styling (grew up in an Evinrude family, but the marina where we put our boat into Lake George was a Johnson dealer, so saw a lot of them on their rental boats).  When I first got mine it was around 70 in both holes and ran, it came up to 75/78 after running it a couple of times.  A note I have of a post by Gary, an esteemed older member is that they’re hard to start below 70PSI.

A couple of weak points to watch out for:

The piston pin can put wear on the top end of the (plain bearing) rod, causing “rod knock”; To check, take out the plugs, and rotate until each pistons is starting to go down, put a dowel through the spark plug hole and push down on the piston and see how much it can move down (without moving the crank/flywheel).  At some point in the 60’s (62 or 63?) they made the rods stronger, and used a larger pin with roller bearings: A set of pistons/rods from the later engines can be swapped in.  Best to  oil at 24:1 without the roller bearings!

1958 and later switched to the smaller/weaker 5.5/7.5 hp lower unit;

The drive shafts are hard to find.

I seem to recall hearing the bottom bushing in the tower can wear and become egg shaped.

 

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