50HP Bigfoot - Lower unit clunk

[MarcusRTJ]

My apologies if this has been covered and my searching skills are lacking. I tried to find something but couldn't.

I have a 1998 50HP Bigfoot 4 stroke hanging on a 99 pontoon that's been very very well taken care of so I'm confused as to why I'm having all of this trouble recently after purchasing it.

A new prop was installed on Saturday and I have taken it on and off a number of times trying to figure out what is going on. When I put the boat in gear without the prop its smooth and silent. With the prop on it sounds like I left a socket in the lower unit until I rev it out then it performs like normal. It does this on the hose and in the lake.

Now, back up a couple days. The other afternoon the boat was running like crap and I reved it with the nuetral button engaged and it dropped into gear. I'm thinking something broke at that point.

If this is the case can things be replaced or do I have to buy a new lower unit?

Please help me out and thank you!

 

[Silvertip]

Re: 50HP Bigfoot - Lower unit clunk

With the engine shut off, turn the prop by hand while you have someone put the unit in gear (forward or reverse). Now rotate the prop back and forth and try to wobble it. If it appears loose, you probably didn't install the prop correctly. If it appears tight then we'll need a little more description on the noise you are hearing. When you shift the engine into gear are you easing it in or using a very deliberate and quick shifting motion. If you are sort of sliding it into gear the noise you are hearing are the clutch dogs grinding against each other. A rather solid clunk is normal if you snap the lever into gear. Continue to make your shifts very slow, that ratcheting noise will ultimately lead to the unit jumping out of gear due to clutch dog wear. If something is broken in the lower it can be replaced.

 

[MarcusRTJ]

Re: 50HP Bigfoot - Lower unit clunk

Thank you very much for responding and sorry for being vague.

I am putting it into gear deliberately as it should be and this knocking sound is at idle speed and it literally sounds like the prop is hitting the lower unit. Its not, I've checked...LOL

I have spun, pulled, jerked, tapped, ect on the prop and put it on by hand and with an impact wrench and even tried the old prop on for comparison. Same scenario either way.

I have even put the prop nut onto the shaft and spun and pulled it that way and there's no slap nor does the shaft feel loose.

The sound is definitely coming from somewhere in the lower unit if you were to ask my ears. I've put my hand on the casing while its in gear running at low rpm and I can't feel anything knocking but the sound is loud enough that I feel like my neighbors are saying "turn that POS off!!!"

Thanks again for the help!