My neighbor gave me his old Troy-Bilt gas edger with a 3.5 HP Tecumseh engine because it barely ran. He bought it used many years ago. I found out it was made in 2006. So I played around with the carburetor and could get it to run a bit better, but nowhere adequate enough to edge efficiency without it dying every 15 seconds. It's pretty old but in decent shape except for the running and the blade belt looks cracked in a few places (new one is only $5 on Amazon). Anyway, I ended up buying an aftermarket carburetor for it on Amazon for $14.50 after finding the Tecumseh carb part number (640339). It also even came with the gasket that goes between the carb and intake manifold. Slapped it on today and the edger runs pretty good now.
Anyway ... my real reason for starting this thread is about a cylinder "leak down" and compression tests I did before deciding to buy the carburetor. Did a compression test cold and dry (no oil squirted into the cylinder) and it came out to 83 PSI. I didn't squirt any oil in the cylinder to do a "wet" compression test, nor a compression test when hot. For a "leak down" test I used my air compressor with a blow nozzle with a rubber tip on it to pressurize the cylinder through the spark plug hole. I slowly turned the motor by hand while blowing air into the cylinder, and listened for escaping air through the intake valve (at the carb) and exhaust valve leakage (at the muffler).
I concluded the intake valve shows no leakage when it shouldn't leak. But I could hear slight air leakage past the exhaust valve when it shouldn't - specifically on the compression and power stroke when an exhaust valve should normally be closed. I also found and download the Tecumseh engine manual and they talk about some engines using "compression reduction" methods to help starting. I found the parts diagram and camshaft part number and found photos of the cam and can't tell if the exhaust lobe is designed to reduce compression by cracking the exhaust valve. I could however tell from the camshaft photo that it does not have the centripetal mechanism to reduce compression for starting. Is it possible they designed the camshaft to always keep the exhaust valve cracked open on the compression and power stroke? I doubt it, but who knows for sure. The engine doesn't pop or sound weird when running, so the valve leakage doesn't seem to effect how it runs. And the "cold dry" compression of 83 PSI sounds about right for an engine like this.
Anyone have any experience with small Tecumseh engines to know if it's normal by design if the exhaust valve is cracked open or is it just too tight? The engine is Tecumseh model LV148EA, 3.5 HP (148cc). Vertical crankshaft and horizontal rod/piston.
Anyway ... my real reason for starting this thread is about a cylinder "leak down" and compression tests I did before deciding to buy the carburetor. Did a compression test cold and dry (no oil squirted into the cylinder) and it came out to 83 PSI. I didn't squirt any oil in the cylinder to do a "wet" compression test, nor a compression test when hot. For a "leak down" test I used my air compressor with a blow nozzle with a rubber tip on it to pressurize the cylinder through the spark plug hole. I slowly turned the motor by hand while blowing air into the cylinder, and listened for escaping air through the intake valve (at the carb) and exhaust valve leakage (at the muffler).
I concluded the intake valve shows no leakage when it shouldn't leak. But I could hear slight air leakage past the exhaust valve when it shouldn't - specifically on the compression and power stroke when an exhaust valve should normally be closed. I also found and download the Tecumseh engine manual and they talk about some engines using "compression reduction" methods to help starting. I found the parts diagram and camshaft part number and found photos of the cam and can't tell if the exhaust lobe is designed to reduce compression by cracking the exhaust valve. I could however tell from the camshaft photo that it does not have the centripetal mechanism to reduce compression for starting. Is it possible they designed the camshaft to always keep the exhaust valve cracked open on the compression and power stroke? I doubt it, but who knows for sure. The engine doesn't pop or sound weird when running, so the valve leakage doesn't seem to effect how it runs. And the "cold dry" compression of 83 PSI sounds about right for an engine like this.
Anyone have any experience with small Tecumseh engines to know if it's normal by design if the exhaust valve is cracked open or is it just too tight? The engine is Tecumseh model LV148EA, 3.5 HP (148cc). Vertical crankshaft and horizontal rod/piston.
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