TIRED, WORN OUT AND PLAIN OUT CONFUSED

I am a 76 year old man with some brain power left but I will admit this one has me and some others just plain stumped.

I have a Tecumseh oh 180 and found a crack in the exhaust port near the flange.
I replaced it with a head from a tec oh 160 after being told they would
interchange. What I am finding is that the engine will turn over very slow and
stop. I put the old head back on and same thing is happening. It acts like it gets to the compression position and stops. I have adjusted
valves on tdc and slightly before and after with no luck. Have also changed battery and had starter tested. I have bypassed the tractor wiring going straight to the starter and motor ground with no luck.

I can remove the spark plug and it turns over well. As soon as I simply touch the spark plug hole, it stops and is if the starter is straining.

I need some ideas folks.

Thanks
James

Been there with the starting system. Since you went direct, it ruled out the solinoid. That was my problem. Take the starter apart and check the brushes and bearings at each end. Mine had bearings that were dry and it caused the armature to drag.
Good luck

It sounds like the starter. Even though you had it tesed, still could be weak. Went through the same thing on my Firebird last fall, tested perfected, would not even turn the V6 motor over.
The OH160 head may have upped your compressions a little as it has slightly smaller chamber putting strain on a possbily worn out starter.
That's how they got the different Hp ratings was changes to head volumes.
Possible your compression release has stopped working, but I doubt it since problem started when you replaced head.

I didn't see where you tried the starter without any load. Pull the spark plugs out to see if the starter spins ok without a load on the engine, if it's ok, install each plug independantly to see if it is one cylinder or the other. That should help you confirm or eliminate the starter. Although I agree with the rest, it certainly sounds like starter.

Sgdorcas, its a single cyl but yes principal is the same.

What are you setting valves at? Should be intake @
.005
Exhaust @ .010.
These motors are pretty touchy with rocker clearances.
I still think starter.

Sorry tahoe, all my tractors are twin Onan, I didn't even think about it being single cylinder, although the HH80 should have fired something in my memory.

Thanks to all you guys for your input; I replaced all cables to two guage and purchsased a Mega
Fire starter. This thing spins fast and I mean real fast now.