91 Johnson 70hp slipping in higher rpm's

[Captain Bart]

I have a 1991 Johnson 70 hp on my 1986 170.  I was out running on a plane today when all of a sudden the rpm shot up and the boat came off a plane.  I thought I hit a sandbar but I was in the middle of the ICW.  I trim the engine down and went to get back on a plane an as soon as the rpm's got up to about 3000 the engine would rev and I had no thrust.  I idled over to a spoil island and checked the prop to see if it was slipping but it was solid.  The controls seem to be working and I can shift through forward, neutral and reverse.  If anyone has any clues, hints or tips, I sure could use them.

[RickK]

Sure sounds like you "spun the hub" to me.  I think it's time to get the prop rehubbed.

[Captain Bart]

I hope your right.  I just could not get it to slip when I manually checked.  I was going to re prop her anyway, so new hub and prop, hopefully that works. I have a 13x17p on there now with a slight cup.  I was going to stay with the same but I was told by a mechanic that it was a little large for my engine. I'm not so sure before the problem, I was getting about 30 mph at around 5800 rpms.

[fitz73222]

Spun hub, you don't have to hit something for them to let go either. Water skiers run into this often. Often you can't tell its spun by checking it manually. When you pull the prop you'll see that rubber hub is separating from the metal insert and is chewed up. Your engine is propped perfectly at 5800 rpm. Stick with 17 pitch.

[LiquidTherapy]

Ya as others said, I had a old Century with twin yamahas. One was spun the other was ok. Side by side no difference. Rehub that bad boy!

[Captain Bart]

Changed out the prop and yeah it was spun.  I took it to a mechanic because I didn't have a socket large enough to take off the bolt, but the mechanic who changed it said you didn't need a wrench and just tightened it by hand.  He said you just needed to hand tighten the bolt enough to line up the cotter pin, which keeps the prop on.  
Is there any truth to that?

[Capt. Bob]

Changed out the prop and yeah it was spun.  I took it to a mechanic because I didn't have a socket large enough to take off the bolt, but the mechanic who changed it said you didn't need a wrench and just tightened it by hand.  He said you just needed to hand tighten the bolt enough to line up the cotter pin, which keeps the prop on.  
Is there any truth to that?

Maybe. :|
 
Wonder what the manual gives for a torque spec? Probably not real high so if you have strong fingers........
I'd still use a wrench and snug it down a tad (not too taddy) and line up the key.

[futch13]

Depending on prop nut, if it is a castle nut 120-144 in/lbs  if it is a regular nut with a s/s "keeper" (sleeve with grooves for cotter pin at top) then the torgue is 70-80 ft/lbs.  If cotter pin hole does not line up, tighten DO NOT loosen to align hole.