Need help with lower unit question

[Pvillegolfer]

I have a knocking coming from my envinrude motor every 15 to 20 seconds. It's like I may have clipped a stump. I have a feeling my lower unit is going bad. The guy that I just bought it from said he changed the prop and it did not do that before he changed the prop. Anyway I checked the lower unit oil and it seemed to be a milky greenish brown color (if that makes sense). Any advise would help. Thanks in advance.......

[Bassmeister]

No chunks of metal? fine silvery flakes is good. If no chunks, change the lube, change the prop and see how it goes.

[Pvillegolfer]

I looked and there were a few on the magnet but not many.

[hopalong1954]

sounds like some water in the lu oil, change it and check after a couple times out to see if more water.

[Pvillegolfer]

That is what I thought possibly some water but I am boat motor retarded.

[ChampioNman]

Welcome to the BBC but let's re-examine here You said feels like you knocked a stump. But the dude you bought it from changed the prop before you bought it? Then he says it didn't do this after I changed the prop? Hope you didn't get the prop shaft on the deal.

[Pvillegolfer]

Thanks Champion. No he said it didi not do it before the prop was changed so i am going to change the prop back to the old one? The guy is working with me so far but not sure how long that will last.

[gearcaseman]

If you have knocking sounds, you have a problem. First thing is check the propshaft for being bent. Put a stationary object within @ 1/16" from the threaded portion of the shaft and rotate slowly and look for in and out movement of the shaft. It sounds as if you have a seal leaking also. You may want to do a pressure and vacuum test to see for sure.