Small Engines (Lawn Mowers, etc.): Craftsman Lawnmower 31P777-0296-E1, blown head gasket, reed reservoir

Question
My husband does not use computers so bear with me I am trying to get him to explain to me what to ask:

The lawnmower is about 5 years old.
Now it's burning oil and lots of smoke.
Oil is leaking from fuel pump,oil in reed reservoir and
oil is being pushed up the dipstick.
Was told it was the pistons but did a compression test and it read 150lbs.
Have it torn down to the piston now, side and inside look fine (shinny and smooth) but lots of oil in there though, the top of the head of the piston is scored and marked up.

If the muffler is broken, (hear stuff rattling around inside) could that a problem because there won’t be any back pressure so the oil is getting sucked back?

do you think it's the piston or rings?

Is it worthwhile to carry on or should I chuck it over the bank into the ocean.

thanks
Monique

Answer
Hi Monique..

I saw this question sitting in the question pool this morning....

You have not told me what the head gasket looked like.  The main cause for the symptoms you describe is a blown head gasket.

To have properly diagnosed the problem I would have needed to do a leakdown test on the engine prior to disassembly.

Take a close look at that head gasket again..especially that thin part between the cylinder and the valves.