Whiff of blue smoke on start-up - B&S 5HP

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  #1  
Old 10-25-07, 07:04 PM
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Whiff of blue smoke on start-up - B&S 5HP

Hi again,

I have an older pre-MTD Troybilt self-propelled muching mower (yes, the one with the reputation for drive issues - mine has been perfect though ) with your typical 5HP B&S lawnmower engine. it always starts on the first pull and runs strong, but invariably smokes blue (oil) for a few seconds on start-up. Once it's running it's clean as can be. Oil level is good, (I never have to add to it) and the plug is never fouled from this issue. Needless to say it didn't always do this, it seems to have started in the last few seasons.

Is this just normal wear and tear and to be expected on a 10 year old piece of equipment? What am I missing? Does this engine have some sort of a "PCV" system (sorry - I'm a car guy and that's the terminology I'm used to) that can become clogged and cause oil to get past the rings?

Thanks for any help or suggestions!

Chris
 
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  #2  
Old 10-25-07, 09:24 PM
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Sounds to me like normal ring/cylinder wear or gas in the oil. I'd use sae30 oil instead of 10-30, if you're not already. Also, smell the oil in the engine. If it smells like gas, then that's the problem. It would be a carb leaking gas into the engine when it's not running. Probably just rings/cylinder though, after 10 years.
 
  #3  
Old 10-27-07, 05:38 AM
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Being a vertical shaft engine the cylinder bore is only slightly above the oil level in the sump. If you are even slightly overfilled with oil and the top end of the cylinder (spark plug end) is on a slight downhill slant oil can creep into the cylinder and, given time enough, can seep past the rings and into the combustion chamber. Just a thought, if you determine the rings are good and you don't have fuel-migration-into-the-crankcase-by-way-of-a-faulty-carburetor, issue. In such case, simply propping the front wheels up a couple inches should do the trick (provided the spark plug is at the front of the mower, that is).
 
  #4  
Old 10-27-07, 11:42 AM
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Thanks for the replies - the mower actually started exhibiting this behavior when I used to run SAE 30 oil, since then I changed to syntehetic, but not because of the oil usage. During the "mowing" season I keep the mower in my garage on a level surface. I'm intrigued by the carb leaking suggestion and I'm going to check the oil for fuel smell - which gasket in the carb would cause this issue, and why would it otherwise run strong & smooth with a leaky gasket?

The oil level brings up an interesting question I've always wanted to ask - my engine has the twist-lock style of dipstick...when checking the oil level, should one re-insert the stick, twist & lock it, then remove it to determine the proper level, or just dip it without lining up the locking wedges (if I'm making myself clear...) and fully seating it?

I always twist & lock and pull it back out. Assuming this practice is wrong, I would arguably be underfilling it...

Finally, assuming correct oil level and type, a good carb that isn't leaking and the smoke is just from wear, any harm in continuing to run it this way? It still has plenty of power and doesn't seem to protest under the load of the blade and self-propelled mechanism.....

Thanks again!
Chris
 
  #5  
Old 10-27-07, 09:35 PM
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Sounds like you're checking the oil right.

The inlet needle would be the leaking part in the carb if a gas leak is the problem.

Running it with it smoking a little won't hurt the mower any, you might have to change the plug once in a while due to fouling though.
 
  #6  
Old 10-30-07, 06:56 AM
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I wonder if it is possible that there may be some condensation residue in the exhaust that is just burning off on start-up.

When I see white smoke I think water, like when water gets into the combustion chamber of a car.
 
  #7  
Old 10-30-07, 12:05 PM
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TJJP77, as for your oil check procedure, the only difference I would recommend is not twisting into operating position. It's just not necessary as the twist is not a cam action. Furthermore, when you do remove the dipstick to check the level don't give it a good heave-hoe, gently pull it back out. Pulling it out in a quick fashion can create a vacuum that will give you a false reading...more than what you actually have in the sump. The Briggs engines aren't as likely to have this happen but the older Kohlers, with two dipstick o-ring seals always would pull the oil up the stick and it's just good practice to take your time when checking the oil level so that you're reading is accurate.

DavidPr, that would be more like a steam than a smoke if water were in the exhaust since it's not being combusted and merely heated.
 
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