1971 Johnson 4hp impeller drive shaft problem

ugmold

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Tried my old 71 4hp Johnson (weedless, I believe) to give it a run, started and then quit after a few minutes on the boat. Started it up again and it quit in less than a minute, I suspected the impeller and heard some sizzling at the power head.

Rowed back, took the engine off and pulled off the gear case. The old impeller didn't look bad, but there was lots of corrosion and gunk. Cleaned it up and got a new impeller. I can't seem to get the drive shaft back into the lower unit to engage with the prop, the shaft looks ok. ?

I might add the gear case is held on by 3 originals nuts and one is a drill thru nut and bolt, PO must have stripped or broken one off, this took a small chunk out of where the impeller housing sits.

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-Ugmold
 

boobie

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Re: 1971 Johnson 4hp impeller drive shaft problem

Is the D/S out of the lower unit ??
 

ugmold

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Re: 1971 Johnson 4hp impeller drive shaft problem

Yes, it came right out while I was moving it around to clean. Thought it would go right back in.
-ugmold

Is the D/S out of the lower unit ??
 

boobie

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Re: 1971 Johnson 4hp impeller drive shaft problem

You can try turning the l/u upside and in different positions to get it back in. If that doesn't do it, you'll have to take the l/u apart, install the pinion gear and drive shaft together.
 

ugmold

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Re: 1971 Johnson 4hp impeller drive shaft problem

Thanks boobie, looks like I'll have to take it apart.

You can try turning the l/u upside and in different positions to get it back in. If that doesn't do it, you'll have to take the l/u apart, install the pinion gear and drive shaft together.
 

lindy46

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Re: 1971 Johnson 4hp impeller drive shaft problem

Nah, it'll go back in. Shine a light down the opening and move the lower unit in various directions until the pinion opening lines up with the hole. Or get a thin (thinner than the driveshaft) rod and stick down in the opening to align it. Then carefully put the driveshaft back in.
 

ugmold

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Re: 1971 Johnson 4hp impeller drive shaft problem

That sounds a little easier, I'll give it a try.
 

ugmold

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Re: 1971 Johnson 4hp impeller drive shaft problem

What I found is the lower unit was clamped in the vice at an angle, setting it upright and the shaft slide right in.

Thanks for the help.

-Ugmold
 

ugmold

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Re: 1971 Johnson 4hp impeller drive shaft problem

Took it out for a cruise and the fuel pump I also rebuilt seems fine. The impeller is not ok. I saw bubbles coming from the holes when I first started up. After a minute the engine sounded different so I shut it down, took off the cowl and it was hot and smokey.

I had only bought the impeller, not the housing etc.
 

pn

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Re: 1971 Johnson 4hp impeller drive shaft problem

on your next round of removal try backflushing all that gunk down w/ water/compressed air to see if all your water passages are clear. is that just corrosion on your lu?
 

ugmold

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Re: 1971 Johnson 4hp impeller drive shaft problem

How would you do that?

Thanks,

-ugmold

on your next round of removal try backflushing all that gunk down w/ water/compressed air to see if all your water
passages are clear. is that just corrosion on your lu?
 

ugmold

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Re: 1971 Johnson 4hp impeller drive shaft problem

Pulled it apart, the problem is/was the shaft won't turn easily. If I take out the impeller it turns free. If I put it back in, loads of friction, even with a smear of grease. I put the old impeller back in (didn't look bad) and it moves a lot free'r but not sure what it should feel like.'

Gear Oil question. Is Mecury brand (Quicksilver, or whatever the name is) the same oil as Johnson lower unit oil?

Thanks.
 

kbait

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Re: 1971 Johnson 4hp impeller drive shaft problem

As for the cooling issue, be sure your impeller plate isn't bent.. needs to be perfectly flat. Won't pump if bent.. you can usually hammer 'em back if they're bent a bit.

As stated ^, make sure the intake to pump is clear. Also, when apart, blow air up the water tube w/a small tube. Air should pass through w/o much resistance. If it's plugged, your waterpump may be working fine.. just can't pump through and you'll have to investigate further..

Good luck!
 

lindy46

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Re: 1971 Johnson 4hp impeller drive shaft problem

The driveshaft will be pretty stiff turning with a brand new impeller installed.
 

ugmold

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Re: 1971 Johnson 4hp impeller drive shaft problem

I put the old impeller in to give it a try. The prop gave a bit of resistance that reminded me of winding an old clock. Started it up and ran it for at least 20 minutes. The cowl felt a bit warmer than expected when I returned, but no head sizzling.

kbait: Wondering if that plate had a bit of a crown center out...I'm also wondering if I had the impeller's vanes going in the right direction with the new impeller.

I will certainly give it a blast of air next time I pull it apart. The housing isn't the cleanest either. I can see why in other threads folks say to get the entire kit. Makes sense.

lindy 46: Thanks, as kbait said, perhaps my plate is not flat and that is what caused the extra friction on the new impeller.

So what about that gear oil, all lower unit oil the same?

-ugmold
 

kbait

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Re: 1971 Johnson 4hp impeller drive shaft problem

Any lower unit oil will work w/your motor. If it's cooling now, I'd just run it. Those motors don't have thermostats.. just smaller ports to help retain heat. If water isn't boiling off after running up to temp, you're likely good. New impellers will make the shaft turn harder.
 

ugmold

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Re: 1971 Johnson 4hp impeller drive shaft problem

Thanks for the help. Appreciated.
 
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