Johnson TN-28 impeller replacement – disassembly concerns

[shoestringmariner]

Can any of you Seahorse Gurus set me straight on the "what to do’s" or better yet, what "Not to do’s" on disassembling a TN-28 so that I can change the impeller? I started to pull the bottom end but it feels like there is some resistance and I’m afraid that it will go "Whiz-bang-ting" and I’ll never get it back together. I’ve located the exploded parts drawings, and that’s all I can find. They aren’t overly helpful and I see there’s a clutch spring that might complicate things

Any advice would be greatly appreciated!

[frankr]

1. Drain the oil out of the gearcase, or you will dump it on your feet later.
2. Disconnect the neutral cable at the neutral lever below the tank.
3. Remove the curved tube that the neutral cable comes out of.
4. Remove the 4 bolt holding the gearcase on.
5. Separate and remove the gearcase from the 1/4" plate above it. If the clutch didn’t come with it, pull it off.
6. You can now remove the 1/4" plate together with the drive shaft, water pump, shifter cable parts. Watch for seal parts that are at top end of drive shaft. They differ according to whether or not the update kit has been installed.

Don’t freak out about getting the shifter cable back in. It feeds up through a copper pipe. BUT Warning–if the top end of the cable is frayed (Step 2&3), don’t pull it out. You will have to use plan B.

[shoestringmariner]

AWESOME, thanks Frank! All I could find was a how to on a newer motor where it suggested removing the entire power head.

[marvk]

I’ll be do in mine this year too. Saving this future reference.
I have already modified a standard impeller to fit the slightly larger shaft.

[marvk]

Bringing up an old post I know, but I finally got around to replacing impeller on my TN-28. I was doing fine following Franks instructions above, until I got to removing the plate with the water pump mounted to it.

I can rotate it a little bit and it moves. But I can’t pull it out. Is there something at the top of it has to be removed or loosened? There’s a large screw halfway up the midsection, does that have to be loosened or removed? As it is now, I can’t budge that large screw.

[frankr]

Put the large screw out of your mind, that has nothing to do with it. There are two things that come to mind concerning the plate being stuck. First is it may simply be the water tube sticking in the rubber grommet. Twist & pull a bit harder. I’ll even forgive you if you get a screwdriver in there for a gently pry. Second is the drive shaft splines may be rusted into the crankshaft splines. Not a good situation. Can you move the drive shaft up and down at all?

[marvk]

Well, good news and bad news. Good news, I finally got it separated. Changed the impeller, good thing, as the old one had 2 broken off vanes. They were large enough that they didn’t leave the pump housing.

Bad news, I shattered the carbon seal on the top of the driveshaft putting it back together.

Does anyone have the part# and where I can get another?

[frankr]

303391 Carbon seal, 303347 o-ring inside it. Same parts used on a bazillion 5.5 and 7.5hp models, mid 1950s-up.

[marvk]

Hi Frank,

That looks like the one used on the cd series mid fifties. This one is a ’53 TN-28 5hp. Looks way different than the one that’s in there. The mid fifties seal is cupped shaped, isn’t it?
This one is more flat.

[frankr]

Then I’d guess you have not-modified version. There was a kit to modify it to the CD seal. I’ll have to hunt for the old-style number–if I even have it.

[Author]

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