'81 mc120, high speed hot, screw back of impeller pump

[merc120_81]

Hello all, I have an '81 MC120, with an MC-1 outdrive.

I am experiencing highspeed overheats.

I am wondering, if this rediculously high priced screw, could be my issue, when installing new impeller housing upper/lower entire kit, the screw I had, didn't seem to get real tight/snug.. i am running with that screw, and am having issues still. could I be sucking air at the back of the impeller housing?

The screw I am talking about is #9 in the diagram here:
9 Screw 10-30720 18-3226

I boats diagram


clear tube test on plane (tube from stern to t-stat housing) a couple bubbles here and there, small go zipping by....

slow speeds runs fine, output test, are inconclusive, as I don't trust my tach. but around 2 quarts of water in 20 seconds at around 750 rpm.

boat runs great otherwise, just gets hot when its run fast (well as fast as my boat will go..lol)

Thanks!

 

[Don S]

Re: '81 mc120, high speed hot, screw back of impeller pump

If that screw was loose it might cause your problem, but I would think the threads in the plastic base are stripped out more than the SS threads on that bolt.

 

[merc120_81]

Re: '81 mc120, high speed hot, screw back of impeller pump

No Perfect seal, or other sealers on the pump assebly process is that correct?

 

[Don S]

Re: '81 mc120, high speed hot, screw back of impeller pump

See if this helps. http://forums.iboats.com/attachment.php?attachmentid=163911&stc=1&d=1344880753

View attachment MC1 RWP.pdf