Small Engines (Lawn Mowers, etc.): Tecumseh 10.5 hmsk105 Pulling/Startting Problem, engine crankcase, valve piston

Question
QUESTION: I have a White Snow Thrower with a Tecumseh 10.5 hmsk105 motor.

The machine is 10 years old.

Last week we had a major snowfall and I was blowing snow for 3 hours straight for 3 days in a row.

All was fine until on the third day the engine started sputtering so I turned if of and confirmed that I was out of gas.

I refilled the gas tank but when I went to pull the starter cord, it moved about 3 inches and came to a abrupt stop.  I then tried it again with the same result.  After a couple more tries I could pull the cord all of the way as per normal.  But when I tried to again the above scenario replayed itself.

When I pull the plug out of the snowblower I can pull the starter cord no problem.

A friend of mine, who had worked on these type of engines in the past, came over and pulled off the head.  He said the cylinder looked in fine shape and that the valve/piston timing seemed correct.

We next pulled of the flywheel and the flywheel key was in fine shape.

After we put it all back to together problem that we were trying to fix was still there.

Any ideas as to where to look?

Thanx,

John

ANSWER: Did you check the valve clearance?

This is a helpful link:

http://www.cpdonline.com/692509.pdf

Does the oil smell like gasoline?  Tecumseh carbs have a tendency to leak gas into the oil.  When this happens the engine can "hydolock" as the oil is thinned by the gas.  This thin mix can fill the engine crankcase with gas which can cause oil/gas to leak past the rings.

With the spark plug removed, does the engine spin?  The compression releases are these engine is ground on the exhaust cam lobe and are very reliable.

Let me know if the engine spins with the spark plug removed and if the oil smells like gas?

Eric

---------- FOLLOW-UP ----------

QUESTION: Hi Eric,

I have changed the oil as someone surmised that the might be the problem - no change in issue.  The oil does not smell like gas.  Another buddy of mine mentioned about the Hydrolock and said that it should spray gas if I pull when the plug is out.  Gas did NOT spray when I pulled with the plug out.

The engine does spin  when the spark plug is not in.

Had the head off but did not check the valve clearance.  What do I have to do to check the valve clearance?

Other ideas?

Thanx for your time and attention to this.

John

Answer
Were you able to open the link?  I keep receiving an error when trying to open it.

If you have the head off, rotate the piston to top-dead-center on the compression stroke and then measure the valve to tappet clearance with a feeler gauge.  Should have about .008 inch for both valves.

It it pretty rare to have too much compression.  Are you using a Tecumseh head gasket?  Should not matter that much but I have seen some guys make there own gaskets and cause problems.

If it turns over with the spark plug removed then most likely all the internal parts are fine.  I have had connecting rod bolts loosen but usually you can't pull the string with the spark plug removed.  

Sounds like you have several tools and folks with engine knowledge.  How much trouble would it be to remove the engine and take off the rear engine case/cover/sump to inspect the conecting rod and camshaft?  Usually the biggest challenge is removing the crankshaft pulley.  If the pulley comes off easy, and using air tools, I can pull and remove the rear engine cover is less than a half hour.  If you decide to do this, make sure the flywheel is facing down when you remove the cover so the camshaft stays inside the engine block when you remove the cover.

Check the valves first before removing the engine cover.

Just to re-cap, you said the flywheel key was fine.  Are you using the correct flywheel key?  Tecumseh has a couple of different styles, one for point/condenser systems and one for electronic ignitions.  Also, have you re-checked the key?  I have had keys shear after I re-assembled and starter the engine.

Eric