Unfortunatly it sounds like your motor is defiantly blown, since its making a clunking sound around 180 deg or turning over the motor then most likely the connecting rod broke at the end where it meets the crankshaft. Look near the sides of the engine, you make see a hole or crack from the impact. How old is your engine? It may be worth a new short block...

its old. 1980 vintage. this is the 2nd shortblock. since the head on this thing is so thin, flathead right? why does everyone refer to getting a shortblock and not a complete motor or "long block". how much extra does the head cost? since it has an oil sump, what kind of rod bearing does it have? roller bearing or is that 2-stroke stuff?

A "long block" is a complete engine. Carb, starter and all those other parts cost extra vs "short block".

You might be able to find a used engine??

ok, 2 hrs of tinkering and the motor is torn down. i took off the side cover and left the flywheel attached. i guess the crank turns 90 degrees, not more. everything looks fine. except i cannot turn it more than 90 crank angle degrees. i got carrued away and took out the piston. now it turns 180 degrees. it has to be something under the flywheel. thats where the mag is , right? oh boy, something electrical. dang, i hate that stuff. mechanical stuff i can handle. now, how do i get the flywheel off with the side cover off. the crank is a little loose now. but the side cover back on, with the cam and other stuff? this is interesting.

I'm thinking maybe a busted cam?
SOME engines had a counterbalance shaft, but I don't know if your's is "big enough". IF so, that could be another potential part.
Can you rotate it enough to make either valve move?

when the side cover is off, the cam comes right out. so i would say the cam is not the problem. its just the crank in the block now. no piston or rod and the only thing that can interfere is under the flywheel.

Joe,

Could be a magnet inside the flywheel has come loose/out
and could be jamming up things. The older H series engines
with points/condenser have 2 magnets inside the flywheel
edge that can come loose. This flywheel is no longer
available, and can be a real problem if the magnet is
destroyed/damaged when this occurs. If you'll post the
spec number of the engine (H70...then spec #), I'll look
and see if there's a COMPLETE REPLACEMENT ENGINE available
for this H70. If so....it'll go to an OHV engine.

T-Man

i did a quick check on ebay and found several flywheels for a tecumseh H70 motor. they look pretty close to mine. i will have to get the flywheel off and check it out. i am curious to see what the problem is. i saw a 5.5hp horiz shaft motor for sale at pepboys for $159. any chance this would fit or is that just a generic go-kart motor? i suppose the odds of it fitting are pretty slim.

ok. i got the flywheel off. on this engine the FW has a backing plate with 2 bolts that hold it too the motor case. seems 1 backed out and stuck to the magnet on the flywheel and was causing the jamming. ok, but it back together. a couple question? cam timing. there is a small dot on the crank gear. the cam gear has a large hole near the teeth that has a groove next to it. there is also a small dot about 8 teeth away that is close to the cam gear center. which of these 2 marks do i line up with the crank dot? also, should i use loctite on the rod bolts? what torque?

Groove

ok. it runs but so-so. i had the governor leakage off and it seems to be sticking now. the idle is sticky. it will run ok but when i back off the throttle, the rpm's seem to stay too high. the gov linkage seems to be binding a little. of course i had the throttle cable off and i messed around with the mixture screw on the float bowl. it ran kinda funky before i tore the motor apart so i guess i am back to where i used to be. but it does run.