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i have a 10 horse tecumseh and every time i pull the starter i shear a key.
what would cause this. i spin the cam by hand and everything is free.

If the keyway in both the crankshaft and flywheel are good, the main cause for shearing would be not properly torqueing the flywheel nut.

never heard of that, usually just use impact wrench to tighten.

oil/grease contamination on the crankshaft/flywheel taper can also contribute to this problem.

You have most likely damaged the key ways.
Check them for burrs and if burred take to them with a fine file.
Then a bit of lapping with some fine valve grinding paste till the whole contact faces is a dull grey.

Careless use of an impact wrench will shear the key, they respond much better to a slow tightening

By using a impact you may have cracked the flywheel.

Been awhile sense I worked on a Tecumseh but didn't they have a off set key in them? If so try putting the key the other way next time and try it, it might be timing kick back.

Rocky J said:

Been awhile sense I worked on a Tecumseh but didn't they have a off set key in them? If so try putting the key the other way next time and try it, it might be timing kick back.

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It is a tapered offset key so will only fit one direction.

No this has a woodruff key.

also i pulled off the flywheel and the key did not shear this time, but it has a kickback like its out of time. so i pulled the pan and the crank gear and the other gear line up right on the marks. so iam at a loss as to why it is out of time.

Is this a overhead valve engine with a compression release on the cam shaft exhaust valve? If it is you probably need to set the valve on it. If the exhaust valve is to loose it will kick back just like it is out of time.

no is an old 10 horse power with points.
HM100-159079D

Set of points and condenser should fix it. If they stuck and were pushed apart with the crank lobe they might of bent and because point gap changes dwell that could be the timing kick you fell. On a car engine you set the dwell (point gap) first then the timing to correct it, the flywheel key is fixed so when gap is wrong it fires a little quick or late. I never had any luck filing them, start today but not tomorrow. When you had the flywheel off did you check the magnets to see if they come loose and moved?

i checked the flywheel and the mags were fine.
never looked at the points though. i will check tommorow. thanks.

checked the points, and they are right on .020 and not burnt.
i think iam just going to junk it. iam tired of tearing it apart. thanks for all your subjestions.
sorry about the spelling.

Tecumseh recommended using the dial indicator tool they had available to set the points gap on those engines. We fixed a lot of VM-80's on Snappers that had been "tuned up" at other shops Especially on recoil only engines. The customers always had the same complaint "ever since they fixed it, it's hard to start" and/or "it snaps the rope out of my hand when I go to start it". You might try going with .021" or .019" point gap and see if it makes any difference. We never had any complaints like that when we used the timing tool. Check and see if you have a pulley loose on the crankshaft or there is a crack in the flywheel keyway. Those also could cause the key to shear.

gave up on the 10 hp, found a tecumseh 8hp. runs good and is solid state. Question is do you think its big enough to handle a 32'' snow blower.

If you have old Tecumseh engine they have point & condenser and that is where you set timing.

i gave up and junked it went with a 8hp. everything is fine now.