Smoking Engine

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  #1  
Old 04-13-04, 07:05 AM
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Unhappy Smoking Engine

I have an older Honda OHV engine on a walk-behind big wheel mower with lots of hours of tough mowing. Every time that I crank it up, I get a good bit of smoke (oil) from the exhaust for about the first minute of running, then the exhaust clears up. If I stop the mower then re-crank it a little later the same day, I don't get the smoke; only when it has been sitting for a day or two. It burns a little oil, but not what I would call excessive, considering the amount of use it has seen. Any idea what may be causing this initial burst of smoke?
 
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Old 04-13-04, 09:04 AM
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The classic answer for the engine you describe would be valve guides. Is your spark plug getting real black? If it ISN'T then you could just be running real rich when you first start. It can be difficult to tell if the engine is running rich OR you are burning oil. Since you said the engine is a OHV model, the guides could be a little worn allowing a little oil to seep into the cylinder while the engine sits. As the engine warms up the valves expand slightly and prevent too much oil from being consumed while the engine is running. I did have an engine (Tecumseh) with overhead valves with known bad valve guides that DIDN'T smoke, but maybe the lubrication system works a little differently in your engine. A Chevy engine with bad guides will smoke a lot, all the time, as well as use lots of oil.

Just my 2 cents worth....
 
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Old 04-13-04, 09:47 AM
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I agree with Jughead. That is exactly what I was thinking. Because of your description, I believe it is your valve guides too. Check them to see if they are worn, if so, you must replace them. If you end up noticing that they are worn, you can get them from any small engine repair shop. They may have to order them. Let us know how it goes.
 
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Old 04-13-04, 10:09 AM
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Hello: thiggy

Also possible some oil is getting past the worn rings while the engine is cool. The engine is a horizontal. Thus the lower side of the pistion is exposed to the oil in the crank case.

Loosely fitting rings caused by worn rings allows the oil to enter the combustion chamber as well as worn valve guides. Most likely a combo of both worn rings and worn valve guides.

An over high oil level in the crank case will cause the problem as well. Oil of the incorrect viscosity will due the same thing in a cold first started engine, until engine heat expands the internal parts.

As can a very slightly loose engine head bolt(s) or warn head gasket, etc. Check the crank case breather as well.

If you need further assistance, use the reply button. Using the reply button moves the topic back up to the top of the daily topic list automatically & keeps all communications in this one thread.

Regards & Good Luck. Sharp Advice.
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  #5  
Old 04-13-04, 11:14 AM
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Holy smokes!

Before you tear apart the engine any which way, answer these few questions first: Is the engine oil over-filled at all? Wherever stored between uses, is it slightly on a downhill slope with the spark plug down? What viscosity oil do you use?
 
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Old 04-13-04, 11:59 AM
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Thanks for your suggestions. I had kind of suspected the valve guides. I am getting some plug fouling, but not much of a problem. I use 30 W discount store oil and the mower is always garaged on level ground. I don't overfill the crankcase. I am not going to tear into this old engine as long as it runs adequately and does not use too much oil. This is the third engine on about a 30-year old mower. I have left a "do not resuscitate" order with the caretaker, in order to avoid taking any heroic measures if it gives up the ghost.
 
  #7  
Old 04-13-04, 02:39 PM
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Shamokin'

Although I agree with jug and Term, Sharp likely hit the nail when he said ring wear, furthermore, cylinder wear as well. Rather than mount a can-holder for your favorite beverage, may I suggest a quart holder for the quart of oil you'll need frequently. I wouldn't start digging the hole yet...as long as you keep 'er full of earl. Run what ya' brung.
 
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Old 04-13-04, 08:20 PM
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I agree. Valve guides don't cause smoking much on small engines. The ring wear/cylinder wear is the problem. The piston is horizontal in this engine, so the oil has a chance to seep past the rings into the cylinder when it sits up unused for some time. Then, when you crank it up, it burns all that oil out of the cylinder...usually takes a minute or so. Older hondas are well known for this, and a new set of rings (around $40.00) almost always fixes it (unless there is other damage, like cylinder wall damage which is uncommon on hondas). I have seen them run smoking like that for years and years. Just keep oil in it.
 
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