Johnson 115 Lower Unit Knock?

[yt]

I have an '83 Johnson 115 on a boat I just bought a month ago. Seems to run great, getting 40 mph @ 5300 RPM on my 17' bowrider. Idles well etc. I am hearing some kind of knock that's at a lower RPM than the motor and only seems to happen when in gear. It's shifting fine and doesn't appear to slip or anything. Last week I finally got around to draining the gear lube and the first couple ounces were pure water then dark gear lube. There was no seal on the drain plug and some metal filings on the magnet. I filled it with fresh lube and new drain plug seals. I do think I may have hit something a couple weeks back. Can I keep running this a while or should I get the unit checked out?

 

[yt]

Re: Johnson 115 Lower Unit Knock?

Just pulled the lower unit vent screw, magnet was covered with metal and I had just put in fresh lube on Friday. Now when I spin the prop I hear grinding. Amazed the thing didn't blow up on the water this weekend. How tough a job is a lower unit rebuild? BTW it's an '82 Johnson V-4 115 not an '84.

 

[Fisherball]

Re: Johnson 115 Lower Unit Knock?

There is a reason rebuilt lower units cost $1,600.00! Buy a service book on the motor, it will tell you in detail. Looks pretty complicated to me. I resealed 1st the prop shaft & lower gear case than 3 years later resealed the top with new water pump housing. I hope I don't have to do the middle (gears & shafts) for a long time or even better, never!

You can open the bottom by the prop shaft & see the gears, could be simply some metal shavings in there you could clean out & reseal. If the gears are starting to come apart (like mine) you know that repair is inevitable!

 

[daselbee]

Re: Johnson 115 Lower Unit Knock?

I never tore into one. But one day I will.
You need special pullers and other tools. Also the shim measurement and placement on the pinion gear is critical. Special tool for that.
Once re-assembled, you then have to pressure test it and vacuum test it.

One day I will get into a LU, but not now.

 

[Fisherball]

Re: Johnson 115 Lower Unit Knock?

My thoughts exactly! Looks like a PITA!!! But if mine goes I will rebuild it. $1,600.00 is too much for me to pay for a repair on a boat I paid $100.00 for!

 

[daselbee]

Re: Johnson 115 Lower Unit Knock?

Hey...
I don't know about the interchangeability...
But I have a 1987 v6 LU that I want to get rid of. It is a 20 inch model.
I may be crazy, but it may fit. You wanna get together on it?

We would have to really figure out the interchangeability issue.


PM me if you want to talk.

 

[yt]

Re: Johnson 115 Lower Unit Knock?

This has the small casing LU that was used on the V4 from '78 - '91. Has the four intake holes with the internal screen Don't think it was used on any V6. There should be a lot of these around, might take a chance on a used one. See them on e-bay and other places for $200 - $500.

 

[wilde1j]

Re: Johnson 115 Lower Unit Knock?

Probably used is a good choice. The hardest parts of the rebuild is getting the bearing carrier pulled and getting the pinion nut off.

The bearing carrier needs a special puller designed to catch two of the webs and the pinion deal needs a special tool to hold the splined end of the driveshaft. If you seriously considering the rebuild choice, I can send you a *.jpg of a puller I made using a hitch drawbar, etc. The other tool is often made by boat shop by welding the lower part of a scrap crankshaft to a 1/2" drive socket or you can buy the pricey BRP special tool