Johnson sea horse jumps out of gear

[Termie]

Hi I have a 10hp 1959 Johnson Sea Horse which starts and runs beautifully, except that when you give it some revs in forward gear it jumps out of gear unless you hold the gear selector. Is this likely to be something that can be adjusted or is it more serious. Thanks Termie

[Joe Reeves]

Termie.... It's possible that the engine has play in its shift linkages, or that the shift linkages have been adjusted improperly previously, which of course will need to be corrected if this is the case.However, the result of the above, and your immediate problem is that the shifter dog (splined to the prop shaft) and most likely the forward gear itself have worn lobes.The lobes protrude out from both ends of the shifter dog and both gears. In forward gear, the shifter dog lobes are forced into and alongside the lobes of the forward gear. The forward gear lobes, effectively grabbing the dog lobes, causes the propshaft to turn. These lobes must retain thefactory machined sharp angled edges.Due to shifting into gear slow, rather than snapping the engine into gear in the major cause of having the shifter dog and gear lobe edges crash against many time before the engine is actually in gear. This causes the lobe edges toround off. With the lobes rounded off, as rpms increase, the pressure exerted on the lobes causes the unit to jump out of gear.Bottom line.... dismantle the gearcase and inspect the shifter dog, gears, etc, and repair as needed.

[Termie]

Thanks JoeMuch appreciated advice.