Reviving a LT-39

[burnt-clutch]

Hey all, I’m onto my next project, a LT-39 that My Dad got years ago, but never did anything with. I’ve checked that it has compression and it does, -62/70 PSI. I squirted some oil/gas mix in the slow speed yoke, and it wants to run. Since these 2 things are in its favor, I’m thinking about making a runner out of it. Have any of you worked on these before, and can you tell me how the impellor works, and what to look for when inspecting the lower unit/prop area? Other than the fact that its the predecessor to my TN-28, there’s little else that I know about this series. Here are some pictures of the fossil.

Thanks in advance for your help!
-Karl

[david-bartlett]

Karl,

Neat looking motor with definite heritage to the TN. Compression and Spark are good to have. You will have a runner in time for Spring.

The water pump is a piston pump operating off the lower, but that is all I know, having not had one apart.

Others will be along with more info, so good luck.

[kevinf]

Hi Karl

I have a few Johnson’s with that type lower units (LT, LS ans HS) but I’m no expert by any stretch. As David pointed out there’s no impeller – it’s a small piston pump riding on an eccentric. Check for wear through in the contact areas. I heard on these forums that a common fix was to solder a penny over the face. Make sure that the small ball bearings in the check valve are in place and free to move.
There is a coil spring in the drive train between the gear set and the prop. It serves as a shock absorber. Check the point where the spring mounts. I have a couple where that has broken/worn through.

At the other end of the motor the ignition is a bit special. It’s got a single coil like an opposed twin and a single contact point. There are grounding brushes on the coil and an insulator under the flywheel that are used to make the coil fire alternate cylinders. Check the resistance across the plug wires rather than plug wire to ground and make sure everything is clean. Make sure as well that the ground points in the insulator under the flywheel are clean and grounding.

There’s nothing tricky in those motors and they run well they’re just a wee bit different.

Other members feel free to jump in and correct me if I’m wrong 🙂

Kev

[burnt-clutch]

Thanks for the replies. I tore into it tonight and got this –

The eccentric seems to move Ok, I guess I’ll take everything apart, clean with Kerosene and then reassemble.
Do I use Lubriplate 105 assembly grease for the gears?

-Karl

[kevinf]

I’m a Corn Head grease fan myself but lots of others swear by Lubriplate.

Kev

[Mumbles]

Here’s the Corn Head Grease. Good stuff!

http://www.greenpartstore.com/John-Deer … 02562.html

[burnt-clutch]

So whats the difference between the Cornhead grease and Lubriplate? I have a John Deere dealer in town that I could probably get this from. Also, does anyone have parts numbers for the felt washer (circled) and the propeller shaft seal? I broke the washer on reassembly, and I’m sure the seal could use a replacing..

-Karl

[kevinf]

The part numbers for the seal were 25-208 for the cap and 25-209 for the cork seal. I’m not sure about the washer but it looks like 41-71. I doubt that you’ll find them and if you do a NOS cork seal is probably pretty fragile by now. Perhaps someone has found a replacement.
One reason for running the new greases in pre-war motors is that they run wet. Seals are hard to find and on some motors non-existent. Personally I don’t try as long as the grease doesn’t run out around the shaft I just change out the grease as required.
I remember breaking one of the gaskets around the pump as well. Seems to me I replaced it with an O-ring but maybe my memory is slipping … I’m sure there are folks out there with parts motors if you want an original replacement.

Kev

[Author]

Posts