symptons of lock-up on bottom piston

[Sandy Davey]

Hi,<br /><br />Have recently inherited an Evenrude 50hp Lark Model 50273C (don't know what year it is). It appears that the carb body and valve assembly have been replaced. Compression seems good at 130psi per pot, but bottom piston is showing symptons of lock-up when plug is in place (turns over ok with plugs removed). Is this indicative of a head gasket problem? As yet have not attempted to start the engine. Any clues?<br /><br />Thanks<br />Sandy

 

[ob]

Re: symptons of lock-up on bottom piston

May be problem with reeds.Will motor turn over with starter and plugs in?Your motor is a 1972 model

 

[DJ]

Re: symptons of lock-up on bottom piston

Davey,<br /><br />Any evidence of the bottom piston hitting the plug??

 

[RICKRICK1]

Re: symptons of lock-up on bottom piston

Davey you might measure the distance from top dead center on each piston to the top of the spark plug threads. You may have wear on the piston wrist pin or at the crank shaft. A simple way to do it is rotate the piston being measured to top dead center, I use a wood dowel thats just smaller than the spark plug. If you keep light pressure on the dowel you will know where TDC is, then scribe or mark the dowel at the top of the spark plug thread on the head. Remove the dowel and measure. Do both pistons, then compare measurements. Additional thougt as I'm not sure, but you may need to be using surface gap plugs. Im sure one of the rude mechs can answer that. Good luck

 

[Sandy Davey]

Re: symptons of lock-up on bottom piston

to OB, [15076] DJohns19 [5471]& Rickrick1 [11834]<br />Gentlemen thanks for your input. Food for thought and some more investigative work required. I'll keep you posted<br />Regards<br />Davey

 

[Sandy Davey]

Re: symptons of lock-up on bottom piston

Got the engine running. Apparently even though the battery had a good charge, it wasn't good enough. Have since tracked down a possible earth leakage.....the joys of older boats and engines that have suffered the ravages of neglect.<br />OB, did the G'box on that engine auotmatically engage when the key was turned off( and consequenly was in gear when trying to start?)