pointandshoot
Cadet
- Joined
- Feb 23, 2010
- Messages
- 22
hey guys, i've been trying to diagnose this on my own but i need a little help. the motor is a mid 80's 9.8 and for the most part it runs pretty good...was a bit of a basket case when i got it a year ago, but i've seemed to get most of the problems taken care of except for this: for the most part i just use this motor as a kicker on my bigger boat, but for fun i pulled it because i wanted to see how it would run on a 12ft aluminium car topper we have up at our cabin. well with just me in the boat it seemed like the prop was slipping a bit but it still managed to get me up on a plane and after that it would push really good. well, add another body in the boat and no frickin way. she'll get up to a certain rpm with a good bite on the prop then just let go. rpms go up, speed drops way off. so its a slipping prop hub right? we did the "mark the prop nut and the prop/hub" test and the marks didn't move. we also have a cherry 7.5 merc roughly the same year up there so i pulled the 9.8 put the 7.5 on the boat with the 9.8 prop (i know its getting confusing) and although it was a little slow getting up on a plane it did it with no slipping (didn't try with 2 bodies in the boat). i was going to put the 7.5 prop on the 9.8 but this is where i stripped the prop nut and for some reason (remember i said basket case 9.8) the 7.5 prop nut would thread on the 9.8 motor. so now i'm back home in my shop, drain the oil. doesn't seem like there's metal, nothing on the drain plug (supposed to be magnetic right?) if i hold the drained oil in the sunlight and let it run by tipping the bucket back and forth there does seem to be a bit of a "pearl" look to it but nothing super crazy. i pulled the water pump and turned the drive shaft in both forwards and reverse, everything seemed smooth and the shifting seemed positive with the vice grips. i really don't want to tear into the bottom end just to see if everything looks good, and it seems like they don't go bad on these motors that often so now i'm back looking at the prop. the prop that i have now is stamped 8P A20, this doesn't seem to match up with anything for the 9.8 (can't find a 48- number) and looks different from the prop we have on the 7.5. so am i dealing with a wrong prop and its sucking air? i'm going back up to the lake in a month with tools this time and worst case scenario is i keep switching parts between the 9.8 and 7.5 until i isolate the suspect part. anyone able to point me in the right direction? thanks in advance.
