48 special lower unit diagnosis

[fireman57]

Have an '89 48 special. Lower unit blew up and replaced it with a known good one. Took it out and ran it for a little while and it was fine. I bought a different prop for it and had a buddy put it on (he had done it several times with his boat so no big deal). He forgot to put the spacer in before installing the prop. Didn't notice it and took it out again but realized pretty quickly that something wasn't right so we pulled it out of the water. The outside of the base of the prop was pretty worn off and the mating surface on the lower unit was pretty ground. Everything nice and shiny like it shouldn't be. Replaced the spacer and prop but now it spins like a spun hub at about half throttle. have put two known good props on it so I know it isn't the prop.
Don't have much experience in lower units but I'm about to get some I think. I understand the basics on how they work with the clutch dog and all and have seen all the parts laid out but can't figure what would be causing this.
Ahead of time, thanks again guys.

 

[Daviet]

Re: 48 special lower unit diagnosis

Doesn't look like there is anything in the lower unit to "slip", a clutch dog will normally "jump" and it feels like you hit something.
How bad is the housing worn, could you be getting some cavation from the exhaust coming out in front of the prop?

 

[fireman57]

Re: 48 special lower unit diagnosis

It's possible that I could be getting some cavitation, I didn't think about that. There is about a half inch gap between the lower unit housing and the prop. Wouldn't think that would be enough to do it though. I know it's not a clutch dog because it doesn't jump. I can't just gun it and take off either or it will "spin". I have to ease the throttle up slowly to keep it from freewheeling.

 

[boobie]

Re: 48 special lower unit diagnosis

There are laby rings inside of the gear case housing that keep exhaust gasses from going over the prop to stop anti-ventilation. With out the trust washer it sounds like you chewed them up. Looks like new gear case housing. Been there.

 

[fireman57]

Re: 48 special lower unit diagnosis

NO! That's not what I wanted to hear.I do have another case because the gearset blew up in the other one so I kept the case because I know they are hard to find. I will compare them both and see if I can spot what you are saying. Would it be possible to heliarc those rings back on this gearcase without melting any seals? I know a damn good welder.

 

[fireman57]

Re: 48 special lower unit diagnosis

Also I forgot to mention that it does it with the other props and one of them fits inside the housing like it should.

 

[boobie]

Re: 48 special lower unit diagnosis

If the laby rings are gone it doesn't make any difference of what kind of prop you put on it. The rings are machined in it from the factory. Check it out.

 

[fireman57]

Re: 48 special lower unit diagnosis

I will. Thanks.. That is something that I never would have looked at. Hey, if you and Daviet get a minute a guy really needs some help with his 55. I think the post is 1976 55 trying to run or something like that. It has about 33 replies. Seems like a nice guy but I am stumped on it for him.

 

[fireman57]

Re: 48 special lower unit diagnosis

Boobie, I looked and I see what you are talking about. The rings are part of the bearing assembly. I noticed that I could see some but not othere. Turns out that when the prop rubbed on them it took the aluminum off it and filled in the rings. Have about 3/4 of them cleaned out. Some flaked right out but the rest I had to do with a chisel. If this doesn't do it how involved is it to just change that bearing assembly. On the surface it looks like 4 bolts but I know there will more to it than that.

 

[boobie]

Re: 48 special lower unit diagnosis

Could you post a good pic of exactly what you have ??