Tecumseh Flathead Engine Overhaul (Part Two)
Article by Mark Trotta
Sheet metal parts on small engines are commonly referred to as engine tin. These include gas tank, blower housing, and pull-cord housing, as well as any shrouds or deflector shields there may be.
Tecumseh H25 Flathead Before and After Overhaul
This is Part Two of the Tecumseh engine build.
Crankshaft, connecting rod, valve seats, cylinder bore, piston and rings are covered in Tecumseh Flathead Engine - Part One
Ignition, carburetor, and engine start-up are covered in Tecumseh Flathead Engine - Part Three
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Restoring Rusty Engine Tin
There several ways to restore rusty engine tin. Media-blasting gives good results, but I don't have access to one, and it would have been an unnecessary step to farm out. Electrolysis is another method, but that's probably better suited when you have more than a few parts to refurbish.
The method described here includes grinding, filing, and sanding down to bare metal. Tools included an air-grinder and die-grinder, a bench-grinder, and electric rotary tool. You won't need all these tools to get the same results; but they are all great tools and serve many other uses.
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Paint Removal
After the blower housing was off the motor, the majority of rust and old paint was removed on a bench grinder with a wire wheel attachment.
Starter Housing Removal
To remove the rest of the paint and the rust from the blower housing, the pull-cord (starter) housing needed to be removed. It is removed from the blower housing by drilling out the four pop rivets.
If you have a drill press, this is an easy chore. If not, a hand-held drill will work, but will take much longer. Drill old rivets SLOWLY with a 3/16" drill and they will come out without incident.
Rust Removal Procedure
Starting with a hand-held piece of coarse Emory cloth, I "checked" or cross-hatched the housing left and right, and then up and down.
The check marks give you a visual of how much you've sanded off, so you don't sand down too far (or not far enough) in one area.
For the heavily-rusted areas, I brought out my 5" air grinder with a 40 grit disc. This quickly removes the heavy stuff, but caution must be used or you'll take too much off in one area. That's why the cross-hatch marks are helpful, to keep metal removal even.
After a couple sessions with the air grinder, the metal was gone over with Emory cloth, making new checking patterns.
I then switched to fine Emory cloth, then die-grinder with a Scotch-Brite pad.
After cleaning, the starter housing was sprayed with gray self-etching primer.
Stainless 12-32 machine bolts with lock nuts were used to reinstall.
Early low to medium horsepower Tecumseh engines have a distinctive "teardrop" shaped starter housing.
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Rusty Gas Tank Repair
Finding a replacement gas tank for a vintage small engine is not always possible. Sometimes, the only alternative is to repair the one you have.
The old paint was removed on a bench grinder with wire wheel attachment.
Cleaning Inside of Metal Gas Tank
Metal gas tank restoration will require the extra steps of cleaning and/or sealing the inside of the tank.
To remove the grit and dirt and loose rust, I started with a dab of household dish detergent in some warm water and poured it into the tank.
After hand-shaking the tank around for a minute or so I drained it out, noticing the now-brown colored water. I repeated this process several times until the water poured out a little clearer.
Does Evapo-Rust Work?
A while back, I watched a YouTube video where a guy soaked a rusty old knife in a container of Evapo-Rust. It seemed to do a good job with the old knife, so I decided to give it a try.
Evapo-Rust is non-toxic and biodegradable, and has no fumes or bad odors. It's also non-corrosive, so it's safe if you accidentally get some on your skin or in your eyes.
After draining, I looked inside and was really surprised at how well it worked. It probably helped that I let it soak for several days.
Repairing A Small Rust Hole
If you have a small pinhole leak in a metal gas tank, a two-part epoxy should work for you. But any larger than that, soldering or brazing may be a better option.
I was fortunate that there was a just one small pinhole on this tank. What also helped was that the original sheet metal was pretty thick.
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J-B Weld Gas Tank Repair
In the past, I've had good luck with other J-B Weld products, so I bought their gas tank repair kit #8217.
The epoxy is a two-part, hand-mixable, non-rusting putty that is also petroleum-resistant. It can be used on plastic or metal gas tanks.
For best adhesion, have the surface totally clean, then scuff repair area before applying epoxy.
Prime and Paint
Before priming, parts were cleaned and dried, then another light scuffing.
The color coat was applied several days later.
After a few more days, the first coat was wet-sanded with 400 grit, then a second coat was shot.
Tecumseh H25 After Overhaul
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Notes and Misc
Depending on where you live, the inside of the gas tank may start to rust up again if not in use. If you're not filling the tank right away, coating the inside with a little oil will prevent rusting. When ready to use, you can either rinse out oil by sloshing a little gas through it, or just leave it and let it burn off during start-up.
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Related Articles:
Tecumseh Flathead Engine Build - Part One
Tecumseh Flathead Engine Build - Part Three
Vintage Go-Kart Build
