1974 70hp Johnson lower unit/impeller ?'s

B

bream buster

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I have a new to me1974 70hp Johnson o/b. Last week I fired it up for the first time. It ran great but wasn't shooting any water out of the water ports. So I decided to go ahead and service the impeller and this is what I found. Here are pics of the impeller and the sand/mud on the housing. I have know idea where to go from here. Where did the sand/mud come from???
 
classiccat

classiccat

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Re: 1974 70hp Johnson lower unit/impeller ?'s

your picture didn't come through but I know where you're coming from!

a "new to me" '75 70Hp who's water pump was 2-decades old...the epitome of Prior-Owner neglect!


To my surprise the impeller was still intact and the waterways in the powerhead are actually reasonably clean.

This is crud that was sucked-up through the intake screens (in my case, both sides were busted), circulated through the powerhead and dumped into the exhaust housing. The water is supposed to drain in the aft-portion of the LU however sediment could collect on the water pump and shift-housing as shown.
 
Watermann

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Re: 1974 70hp Johnson lower unit/impeller ?'s

The PO ran in shallow water, prop stirred up the sediment and the water intake sucked it inside the cooling system. It's very common. Check the intake screens on the LU to make sure they don't have some larger particles stuck in the holes.

Wow Bluefin, that is unreal, I've never seen so much muck collected inside a LU.
 
B

bream buster

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Re: 1974 70hp Johnson lower unit/impeller ?'s

Sorry it took so long for photos! I had to re-size them and i'm a newb lol


ResizedImage_1371315989705.jpg

ResizedImage_1371311001885.jpg
 
B

bream buster

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Re: 1974 70hp Johnson lower unit/impeller ?'s

Ok, fellas I have tried everything thing but still can't get water flow from the thermostat housing to the water exhaust ports. Everything else is clear from the lower unit and up to the thermostat housing. Thanks for all the previous replies. And if it helps my case its on an 1987 Bluefin Sportsman. Gotta love the tin boats!
 
B-Dozer

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Re: 1974 70hp Johnson lower unit/impeller ?'s

I just got a 1976 70 hp evinrude and i had the same problems . My advice to you is add a tell tale. Thats what I did anyway. there is a previous post with all the info you need. I will try to find the post quick
 
B-Dozer

B-Dozer

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Re: 1974 70hp Johnson lower unit/impeller ?'s

ok not sure how add link but I just searched Add a water pressure indicator on omc outboard and it popped right up There is a picture of your motor and where to put fitting
 
B

bream buster

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Re: 1974 70hp Johnson lower unit/impeller ?'s

Thanks man! I actually have the thermostat housing off and I'm trying to flush it out to the water exhaust ports.
 
Watermann

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Re: 1974 70hp Johnson lower unit/impeller ?'s

So what are you trying to do? Are you putting a hose in the t stat opening and wanting to see if water flows out of the 2 exhaust ports on the middle section leg? Nothing will come out of those holes until there is back pressure from the lower until being submerged in water. Nothing will come out of those 2 ports even when using muffs, only the prop exhaust.
 
B

bream buster

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Re: 1974 70hp Johnson lower unit/impeller ?'s

Oh... I see said the blind man! Thanks for the clarification! I assumed it was just and open passageway to the 2 ports on the leg. Now I understand the reasoning behind the mod. Thanks B-Dozer and Watermann for the help. Happy Father's day guys!
 
B-Dozer

B-Dozer

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Re: 1974 70hp Johnson lower unit/impeller ?'s

Thanks for adding the link watermann. You are right about taking some stones to drill that sucker out. but it was simple. and no more guessing if its pumping water.
 
classiccat

classiccat

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Re: 1974 70hp Johnson lower unit/impeller ?'s

if yours is like my '75 70, the top of the block is very crowded so I went with the cylinder head (convenient since I have it torn apart).

You're threading a needle a bit hitting the water jacket. I purchased the OEM 90-degree fitting and needed to offset it for clearance.

If you work-up the courage (and don't advise liquid courage for this mod!), these pics may help you out.





 
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