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Cranks and runs great until I run into high grass and engine dies...... usually after about 45 minutes or so. Then when you try to crank it.. the engine acts like the piston is swollen and will not turn over. If you raise the mower.... you can move the blade back and forth but can not crank with rope will not turn over..... really afraid I'll brake the rope..... not sure if crank shaft is going bad or possibility of the safety on the handle is not releasing to crank.

Briggs 125cc engine? When this happens, is the deck clogged with grass? A deck clogged with grass could make the starter rope hard to pull. Are the cooling fins clear? Maybe the cooling fins are blocked, and the engine is overheating. Remove the engine shroud. The fins should be easy to check. Is the oil level correct? Again, lack of oil could cause overheating.

How old is the engine? Has maintenance been kept up on it?

Thanks for the reply, GearHead.... Correct 125cc engine..... deck is not clogged with grass..... I'll pulled the engine shroud to check the cooling fins and they are clean..... Oil level always checked and full....... Unit is old.... but maintenance has been kept up..... now that engine is cool..... tried to pull but still hard. backed the blade back a whole round and tried pull starting again.... not binding up..... it will start..... but would like to fix before the engine drops something and become fatal.

GearHead36 said:

Briggs 125cc engine? When this happens, is the deck clogged with grass? A deck clogged with grass could make the starter rope hard to pull. Are the cooling fins clear? Maybe the cooling fins are blocked, and the engine is overheating. Remove the engine shroud. The fins should be easy to check. Is the oil level correct? Again, lack of oil could cause overheating.

How old is the engine? Has maintenance been kept up on it?

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Do you work on your own equipment? If so, try the following, and check operation after each step:
- Check the blade brake and cable. Make sure the brake is not dragging when the engine is hot. If you reach under the mower, and turn the blade on a hot engine, first remove the spark plug wire. I would just pull on the starter rope slowly (or have someone pull it) while checking that the brake is not rubbing on the flywheel.
- Set the gap on the coil. Maybe it rubs on the flywheel when the engine gets hot. A business card works well.
- Set the valve clearances. Not sure if this engine has a compression release. Larger engines do, and out-of-spec valves can make them hard to start.