Vintage Tecumseh Engine Build

Article by Mark Trotta

After sitting for decades with a seized piston, this rusty old Tecumseh was restored to it's former glory. The fact that it was rebuildable after 50+ years is a testament as to how well these small engines were originally made.

vintage Tecumseh engine restored
Before and After Tecumseh H25 Engine Build
how to rebuild a flathead Tecumseh engine

Engine Disassembly

Before starting engine teardown, the entire motor was sprayed with WD-40 and let it soak for a over a week. Occasionally, I would walk over to it and spray it several more times.

The longer it soaks, the better the penetrating fluid will work.

Vintage Tecumseh engine build

Starting with the blower housing, the motor was disassembled, one part at a time.

rebuild vintage Tecumseh engine

I kept track of the disassembly steps by taking step-by-step pictures, and also wrote down notes in a notebook. This proved to be invaluable later on, while reinstalling the governor and carburetor linkages.

After removing the cylinder head, this is what I found.

rebuild tecumseh flathead engine

Most of the cleaning was done with cans of brake parts cleaner, compressed air, and shop towels.

rebuild Tecumseh flathead engine

Once the side cover was removed, I found this nasty sludge build up--no wonder the motor stopped working!

rebuild tecumseh flathead engine

Engines that have been run on non-detergent oil will often have a thick sludge build-up.


Frozen Piston

The piston was stuck solid in the bore and would not move, because the rings were "frozen" to the cylinder bore.

remove stuck piston in small engine
Read: Remove Stuck Piston


Valves and Seats

After removing the valves, I turned my attention to the valve seats, which were corroded. On small-frame Tecumseh engines, valve seats are not replaceable!

small engine valve spring compressor
Read: Integral Valve Seat Repair
replace valves on small engines

The exhaust valve had very little wear and was reusable after being cleaned up with a wire wheel. The intake valve was too corroded and had to be replaced.

replace valves on small engines

Fortunately, intake valves for the Tecumseh H25 were still available (exhaust valves are obsolete). New valve springs were also available and also replaced.


Block Inspection and Cleaning

Once the motor was completely disassembled, the entire engine block was sanded down. Smaller parts (valves, bolts, etc) were wire-wheeled. The bolt threads were cleaned and threaded bolt holes were tapped.

vintage small engine build

With the exception of the broken or missing ones, I was able to re-use the 50 year-old nuts, bolts, and washers.

how to rebuild a Tecumseh flathead engine

In non-ball bearing small engines, the crankshaft rides directly in the aluminum block and side cover. These surfaces must be smooth and round.

If the side cover bushing is badly worn or damaged, the cover can be replaced. If the engine case bushing needs replacing, consider having a machine shop do this, or finding another block.

Next up was checking and measuring the crankshaft and connecting rod for wear and replacement.

small engine piston removal
Read: Tecumseh Crank and Connecting Rod Inspection


Engine Reassembly

On Tecumseh H25 engines, the crankshaft gear is pressed on. If it has severe pitting or missing teeth, it needs to be replaced.

Tecumseh h25 crankshaft

When installing crank gear, the dot faces out so you can line up the timing marks.


Tecumseh magneto repair
Read: Tecumseh Points Ignition


Install Piston Rings

Instead of a small engine ring compressor, I used an automotive hose clamp to install rings on this small-bore Tecumseh.

install rings on small bore engine


Blower Housing And Engine Tin Restoration

Most old Tecumseh engines are painted either red, white, or black. This one was originally white, so that's what color I re-painted it.

restore vintage small engine
Read: How To Restore Engine Tin


The last part of the engine build was finding a proper carburetor, adjusting the governor, and finally, engine start-up.

Tecumseh flathead engine build
Read: Tecumseh Carburetor Replacement
old school go kart engine


Related Articles:

Vintage Tecumseh Engine Identification
Tecumseh Crank and Connecting Rod Inspection
Integral Valve Seat Repair
Tecumseh Points Ignition Repair
Remove Stuck Piston From Cylinder Bore
How To Restore Engine Tin