This is part 3 in a series on fixing the water cooling system on my Johnson 6hp 1967 outboard (part 1, part 2, part 4).
To start my dad and I set up a makeshift outboard stand using a folding workbench, a 2×4, and a large steel clamp. Not as nice as Peter Nielson’s (link) but it got us rolling very quickly for free on day one when we had more pressing issues. Don’t forget to weigh down the opposite side, we used jugs of oil found in the garage, but down-rigger cannonballs or dumbbells would’ve been perfect.
We also set up a small bucket of water to cover the water intake. In retrospect it may have been too small to allow for proper cooling and suction (more in part 4). I don’t think it was an issue but, if you’re still in the planning stage, plan to use a full (clean) garbage can or a bucket that at least covers the lower unit above the bulge where the impeller housing.
Dis-assembly and Impeller Replacement
To remove the lower unit (as described in detail in the videos by James from Highland Outboards mentioned earlier) you need to release the 4 or 5 exterior bolts surrounding the large bulge (surrounding the impeller housing), then wiggle the lower unit down gently an inch or so until you can see this soft brass screw/bolt. Magnets won’t work so plan to have a very small diameter socket wrench extension or/and some needle nose pliers to make your life easier. A headlamp is also helpful so you don’t annoy each other talking about the right angle for lights.
After releasing that shift rod screw it’s easy to slide off what is generally called the “lower unit” and drive shaft, to expose what the Johnson website diagrams calls the “gearcase group”.
We had to clean a goopy mess of oil mixed with salt water, before we could see the impeller housing screws clearly.
This is what it looked like cleaned up, helps understand that bulge in the exterior housing:
Next step was to release the 4 screws holding the impeller housing on. In our case they were seized. We applied liberal amounts of WD-40 and waited a few minutes, but the flathead screws were stuck and the heads started stripping! Luckily one of my parent’s neighbours Peter is a mechanical engineer who actually worked for Johnson in the early 1970s and he had a trick of using a handheld propane torch on low to put focused heat on just the stainless steel screw heads for about 3-5 seconds. Be extremely careful because the impeller housing is zinc which is soft and will deform if you put direct heat on it.
The combo of the WD-40, waiting 10 minutes, and applying heat did the trick. Later we bought new screws with squareheads to avoid the stripping problem in the future (Note– I need to replace them again because we didn’t get stainless steel :P). So finally we were in to see the impeller itself:
I think my dad had shoes on at the beginning of this session, but somehow he’s barefoot again here… Anyhow, it’s a good thing I like taking photos while other people work because the direction that those fins spin in is part of the mechanical design and you must remember which way they turn when you are forcing the new impeller into the housing. And Peter suggested there isn’t a universal rule so pay attention to whether it’s clockwise or counterclockwise and hope the last person did it right. By the way, despite what the videos say, when Peter saw this impeller he thought it still looked mechanically sound and suggested keeping it onboard as a backup if I ever needed it in a pinch.
Once we had that part out we were able to run all over Nanaimo B.C. looking for a replacement until Dean at MPS saved the day with his excellent stock. Note that this Sierra Marine Engine and Drive Parts 18-3001 (replacing the 1968 0-277-181) was only $21.31 including tax at MPS and is $25.29 online from Evinrude / Johnson. So it pays to check out your local marine supply stores.
Note that when you’re squeezing the new impeller into the housing it’s a very tight fit and you really need to press it in there and get the fins pointing in the right direction. And pay attention to the little pin that slides into the center hole along the drive shaft.
Once the impeller housing is back together, putting the lower unit back on can be a big pain. You need to get the drive shaft into a small hole that leads to the engine block way at the top in the dark, you need to make sure the copper tube slides into the plastic hole on the top of the impeller housing, and then you need to wrestle the gear rod into the right spot to get the screw back in. When all that aligns it feels smooth and easy, so try to do some deep breathing and just poke around until it clicks.
We ran it and no water came out – that was disappointing. So our first thought was that we did something wrong putting the impeller in, so we disassembled everything again. I’m glad that we did because I actually noticed that the new impeller was such a tight squeeze that shavings came off and went up into the chamber that leads up to the copper tube and then the engine block. I hope a good water flow would wash that rubber dust out, but it’s something to be aware of I guess.
When reassembling it a second time we followed Leeroy Wisner’s advice and lubricated with a bit of vaseline. If you click to zoom in you can see how the tips got a little shaved into place:
Unfortunately after a slower reassembly (at the tired end of the day), there was still no water spitting out the exhaust.
Initial Investigation of Thermostat
Since replacing the impeller wasn’t enough, the next step was to try and isolate the location of the issue by pouring some water up from the bottom of the system into the copper tube that leads into the engine block. The water didn’t get too far which hinted that there was a block somewhere up inside.
We had a bit of time, so we took off the top to try and pour some water down from the top of the system. Here’s the top of the thermostat housing, the 3 bolts were tight but they actually came out with a bit of coaxing!
Having opened the thermostat we tried to check the short tube heading out to the exhaust exit (the easier part to check), it seemed clear:
We tried a bit of water out the exit and then on top of the thermostat. It didn’t really get past the thermostat so that seemed to be the next big hurdle:
But that was the end of the day, so the next step was to pack up and call up the big guns and bribe Sam and his dad with some coffee and donuts. Next steps were to replace the thermostat and try to clear out whatever is blocked up inside the copper tube that winds through the engine block?!
(Spoiler alert- pouring water up from the bottom and down from the top & doing everything back up & leaving the motor in a hot car for a week seemed to loosen up the salt chunk a bit.)
Aside on Clamp Screws
Also, while we were at Parker Marine and Marine Parts Supply they both confirmed that the Johnson Clamp Screw Kit (0-388-346) was $105 Canadian!! I am really glad Evinrude/Johnson still makes parts available, but in this case the default thread for a 5/8″ by 2″ bolt from Home Depot worked just fine (we didn’t need this handy advice http://www.bola.de/en/technical-information/screw-joints/determination-of-thread-types.html) and I couldn’t justify the $100 difference this time.
3 thoughts on “Johnson 6hp 1967 Outboard Part 3”