1970 Johnson 20 hp

[Soot87]

I picked up a 1970 Johnson 20 hp for $40 and low and behold it starts but it’s pumping no water so I need to change the impellor. I’ve done this on an old mercury so I have a general idea how to do this and have watched a few videos of similar engines. My question is the shift linkage flat head bolts seem tight and I can’t seem to get a ratchet on them. Is there a smart way to get tight bolts off without striping them. I really do not want to do that. Thanks for your help.

 

[wrench 3]

Work on getting a socket in there. Grind one down if you have to.

 

[F_R]

Get a better socket. 1/4" drive sockets will generally be thin enough. Those bolts should be 3/8" wrench size. If they are something larger, somebody has messed with it and that may be your problem.

 

[racerone]

1/4-28 fine threads on them.-----A salt water motor ?-----A bit of heat may help------One of the bolts MUST be taken out to remove lower unit.

 

[Crosbyman]

try a small impact screw driver & socket but before you do…... soak it a bit with a lubricant like wd40 or PB

 

[Soot87]

Ok got it off and the lower unit. I opened the impeller housing . I’m some what reasonably sure the impellor key was missing and that I didn’t drop it. Which would explain it not pumping any water. Any thoughts on that? Also my boat motor guy says you can just pull the thermostat out. Thoughts about that? Thanks for your help.

 

[racerone]

No you should make sure the thermostat is in and working properly !!-----Post a picture of the impeller that you found in there.------Not much can go wrong other than the vanes breaking off.

 

[Soot87]

Here’s the impeller and thermostat

 

[racerone]

That impeller should pump water.----Was tube inserted into grommet in the exhaust housing and in the pump ?

 

[Soot87]

Right which is why I’m wondering if there was no impeller pin and that’s why it wasn’t pumping any water. Maybe somebody couldn’t figure it out and gave up.

 

[racerone]

Install the drive pin and test run it.

 

[Soot87]

I’m going to have to get one first so more posts to come

 

[Soot87]

Where is this water tube gromet also should there be a seal under the wear plate of the water pump housing?

 

[wrench 3]

The only thing under the wear plate is the oil seal for the gear case.
The water tube grommet is in the top of the "pipe" coming out of the top of the pump housing.
The pin you need is here. https://www.iboats.com/shop/brp-pin-300771.html
Unless that impeller looks brand new I'd replace it while you're in there. https://www.iboats.com/shop/sierra-18-3002-water-pump-impellers.html There not worth that much.
And I agree with racerone. It will run without a thermostat but it will run better with one in there and it won't carbon up as much.

 

[Soot87]

You guys are great thanks again. Pin, gromet and impeller are in the mail

 

[racerone]

There are 2 grommets.-----One in the exhaust housing too.-----And the water tube in inserted into the upper grommet BEFORE installing the lower unit.

 

[thatone123]

If run in salt, it can also be loaded up with salt in the power head water passages. You will need to remove the head and clean out with some wire. I have cleaned out half a box of Morton salt from some 15's.

 

[wrench 3]

In my experience if the pipe stayed in the top grommet you're best to leave it alone.

 

[Soot87]

So the I impeller came today. Waiting for the key to arrive. I was looking at how to take off the housing and the big metal rod that it spins in pulled out. I put it back in just fine but was wondering what my ramifications are going to be on the top? I’m sure there is female part at the top that will also need to seat. Any thoughts here? Thanks

 

[F_R]

Where is this water tube gromet also should there be a seal under the wear plate of the water pump housing?

You should seal the pump plate where it sits on top of the gearcase. Most any kind of gasket cement will do for that. Nothing needed between the plate and pump housing.