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BIG St/12 Problem! Need Some Guidance.

540 Views 3 Replies 2 Participants Last post by  Tractor-Holic
So i Aqurired a sears st12 and the techumseh is frozen from old age! I know how to break an engine loose and whatnot but advice Never Hurt have not tore into this one yet. incase of inrepairable emergency, what motor could i put on that wouldn't require much change to the tractor belt functions and whatnot?
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Take the spark plug out and put some penetrating oil in the cylinder--Marvel Mystery Oil works well for this,or automatic transmission fluid with some acetone added is good too..let it soak for at least a day or longer,before attempting to turn the crankshaft --when you go to try turning it,if it breaks free fairly easy with a back and forth rocking motion,resist the temptation to whip it right over a full revolution..
Go slow,and "feel" for any serious binding or a sudden stop--it could have a stuck valve and you can end up breaking the camshaft if you forced it...often going back and forth a little at a time will allow it to go a full revolution ..
Once you get it turning freely,add some motor oil to the cylinder again..

Often an engine will fire up and run once it is freed up,but you might want to remove the cylinder head and inspect it for any large chunks of rust,carbon,etc..also look for any tiny throttle shaft screws,these often get inhaled on these engines!..
I recently bought a good HH120 Tecumseh and though it spun freely and had great compression,I am glad I took off the head and looked--sure enough,a carb screw was imbedded in the head above the exhaust valve,and the piston was all dinged up--but not a scratch on the cylinder --had I just fired it up,it would have self-destructed in a matter of minutes probably..:eek:..

Its not often the bottom end seizes up,unless it filled with water and sat "forever" or the rod has scored the crankshaft its unlikely to be any problems..
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Thanks for the info and tips, do you know of any other motors that could fit right in, in case it becomes cost ineffective?
The only ones that "fit right in" are what came in these tractors--but with some minor diddling around,one of the cheap honda clones will fit and work well in them,so will most horizontal shaft Briggs,Kohlers,and even Wisconsin's,if you dont mind drilling some new holes,maybe have to re-work the clutch idler pulley,and some other details like the muffler or air cleaner..
--several threads on this forum show how other members have installed "new" engines to Sears Suburbans and Custom/Compacts...
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