Small Engines (Lawn Mowers, etc.): Oil Leak on Craftsman engine, replacing cylinder cover gasket, head gasket, oil leaks

Question
Hi Eric ,
I have an oil leak on my Craftsman mower (Tecumseh engine, sears # 143.006706).  About 1 tablespoon of oil leaks onto the mower deck after a hours run, primarily from the front, under the cylinder head.  Leak doesn’t start until the engine is hot.  I suspect the gasket between the upper and lower parts of the engine.  I removed the blower housing, cleaned the engine and looked for the leak.  Doesn’t seem to be any leakage on the top part of the engine, all leakage seems below the gasket and drips to the mower deck.  Also, it is very clear that at on one side of the engine, there is a small amount of oil leaking right on the gasket – not enough to pool on the deck, but clearly a leak at this gasket.  No leakage from the tube from breather to air cleaner.  No leakage apparent around the breather.  Engine runs very smoothly, starts on first pull cold or hot and was well maintained.
1) Any hints for removing the “cylinder cover” (lower part of the engine), replacing the gasket and reinstalling cover?  I’m especially concerned about the oil seal.  Do I need to replace?  Are special tools needed?  Any hints for keeping all the parts (governor, camshaft, together during reassembly?  Any hints for separating the two parts of the engine?  Or, I am realistically looking at a new mower?
2) I ruled out head gasket and breather, but are there other checks that I should do to make sure that these are OK?

Thanks,
Mike

Answer
The lower part of the engine is often called the oil pan, sump or lower engine case.  These engines are not prone to leaking oil around the sump but it can happen.  Are you sure the head gasket it not leaking?  It is more common for these engines to have loose head bolts which could cause a small leak.

If you have to remove the sump you need to wash the engine and sand the crankshaft to remove all dirt/debris and rust.  With the engine starter sitting on bottom, i.e, the engine upside down, you can remove the sump.  If you are careful the cam and oil pump will not move.  No need to take these parts out.  If you have to replace the gasket, that is removing the sump, I would replace the lower main oil seal.  PVC pipe make a great seal driver.  Pay attention to the depth of the old oil seal before removing so you know how far to drive the new seal.

Refer this link before working on the engine:

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

I would check the head bolt torque and wash the engine with engine degreaser before removing the sump.  It is not very hard to remove the engine so you can really clean the area where you seupect the oil leak is.

Eric