Small Engines (Lawn Mowers, etc.): Honda Gx670 burning oil, valve seals, leakdown tester

Question
QUESTION: Hi Eric,
You probably remember that I asked you a few questions concerning a carburator and ignition coil problem on a stump grinder with a GX670-24hp ? Well I solved these problems, the engine is running fine, but uses oil only on the front cylinder (starter side) The spark plug of this cylinder is black while the other one is nice grey-brown. The oil consumption is about 200-300 cc per hour when stump grinding. Every time I engage the clutch or when the grinding wheel has heavy friction on a stump, there is blue smoke coming from the exhaust.
Where should I start my search for this problem ? Valve seals ? Piston rings ? The engine has run about 450 hours, but I must say in very dusty conditions (stumpgrinding).
Should I start by taking off the head ? How can I see where the oil is being sucked in the cylinder ?
Your advice plse, thank you !
Pascal

ANSWER: The best tool to use to check compression components is a leakdown tester.  I would initially suspect the rings or valve seals/guides but again a leakdown test would help narrow down any faulty components.  

Is there any other issues with engine performance other than burning oil on the one cylinder?

Eric

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

QUESTION: Thx for replying.
The engine performs well, runs smootly like any other Honda. There is just blue smoke. In my search for the carburator problem, I already performed a compression test, and it was about equal on both cylinders.
How do you perform a leakdown test ? Is it the same as a compression test ?
Brgds
Pascal

ANSWER: Below is a leak on cylinder leak down testing:

http://www.carcraft.com/techarticles/116_0406_cylinder_leakdown_tester/index.htm

The main difference between a compression and a leak down test is you can determine if the rings, valves or head gasket are properly functioning.  Another advantage is you do not have to remove any parts except the spark plug to perform the test.

Does the engine constantly produce blue smoke or just produce blue smoke when you start it up?  Do you have to add oil everyday?

Let me know.
Eric



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

QUESTION: So if I understand this correctly, you put pressure on the cylinder en see with a pressure meter if it goes away ? Which device are you using to perform this test ?
The engine only produces smoke when it has to "work", so when the cutting wheel on a stump is slowing the engine down and the governor opens the throttle.

Answer
When doing a leak down test you are measuring how much air stays/remains inside the cylinder.  You install one end of the leak down tester into the spark plug hole, just like a compression gauge.  Rotate the engine so the piston of the cylinder you are testing is a TDC on the compression stroke.  Hold/lock the engine at this position.  On the other side/end of the leak down tester, you connect an air compressor and force air into the cylinder.  The first leak down tester gauge is used to measure the air input.  The second gauge tells you how much air the engine is leaking.  If rings or valve guides are really wore out you can usually hear air blowing past the faulty parts.

I have seen Briggs and Stratton engine smoke when put under a load but the smoke generally clears up as they continue to run under load.  One reason the engine make smoke when it it first loaded is a loss of vacuum.   This vacuum loss is normal whenever you accelerate any engine.  

What weight of oil are you using?

Eric