Johnson 10 hp 1957 onward

MOTION LINE

Seaman
Joined
Oct 9, 2004
Messages
74
I found a Johnson 10 hp. 1957 at the junk yard yesterday, to my surprise found out that middlesection and the gearcase are the same as <br />used on the 18 hp. model including the rear bolt<br />that holds the case to the middlesection.<br /><br />When did JOHNSON switch to the smaller gearcase which they used 1961-63?
 

Chinewalker

Fleet Admiral
Joined
Aug 19, 2001
Messages
8,902
Re: Johnson 10 hp 1957 onward

Hi Bolaget,<br /> That would be 1958... They took the 5.5/7.5 unit and added a heavier driveshaft and pinion gear. It worked okay, but didn't hold up to the abuse that the 15/18-derived unit could... If you do find a good 4-bolt 10hp unit from 1958-up, be sure to check all seals, bearings and clutch dog before using. If you can keep the water out and the clutch dog & bearings are in good shape, you should be alright...<br />- Scott
 

MOTION LINE

Seaman
Joined
Oct 9, 2004
Messages
74
Re: Johnson 10 hp 1957 onward

Thank you Scott!<br /><br />As a matter of fact I own one 10 from 1963<br />which seems to be OK!<br />However, it took me by surprise when I found out<br />that even the piston and and conrods are different on the 1957 model (much lighter)!<br /><br />Why on Earth did they make the modification, problems with the earlier parts???
 

Chinewalker

Fleet Admiral
Joined
Aug 19, 2001
Messages
8,902
Re: Johnson 10 hp 1957 onward

Hi Boleget,<br /> With the powerhead items they improved the motor over time. They added heftier bearings at the wrist pin end of the con rod, went to a smaller flywheel, improved oil scavenging, etc. You'll find a lot of the '50s 10s with "ovaled" wrist pin bearings as they would wear at that point, leading to knocking and eventually failure. The later rods had a wider bearing to improve distribution of the forces. The lighter flywheel put less strain on the crankshaft.<br /> With the lower unit, they were looking for economy. They lightened the motor a bit by going to the smaller lower unit and made it cheaper to build. It reduced the potential longevity of the motor as you'll find a lot of those 10s (and the later 9.5s) that chewed up the units. They work fine in normal operation, but they can't take a ton of abuse (which is more like "real" world "normal" operation). A little ding in the prop to throw things out of whack might not bother the bigger unit as much as it does in the smaller unit, etc.<br />- Scott
 

MOTION LINE

Seaman
Joined
Oct 9, 2004
Messages
74
Re: Johnson 10 hp 1957 onward

Thank again Scott,<br /><br />I had a closer look at the engines and and found out that the flywheel is heavier on the 1957 model, even the connecting rods+ the pins are smaller!<br />I was just thinking the weight difference in the<br />piston-conrods must have an impact on the ballancing of the engine?<br />Think I am going to use those later parts on my 1957!
 
Top