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Discussion Starter · #1 ·
High folks. I have an issue with my craftsman mower, which has a B&S 19HP 500cc Intek air cooled engine burning oil on startup. Last year I rebuilt this engine with new piston ring and gaskets and what it does is when first started it will blow oil smoke heavy for about 1 minute then clears up and runs fine after that. If I shut it down and start it up again in a day it burns very little oil on start up but if I let it sit for a week ( I usually mow on weekends) it will do the same thing, blow lots of smoke for about a minute. It is blue white smoke so I kow its oil. Before I start taking this whole thing apart my question is what can be causing this. Is the ring I put in bad? or maybe a leaking head gasket? The thought of taking this thing apart again right before mowing season starts is depressing me. Any advice would be appreciated.
 

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You might have a bad valve guide too! The vacuum from shut-down may let it drip in over time! Is your a fuel pump model? I had one with blown head gasket do this also!
 

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Could be worn out valve guide seals. Did you replace those when you rebuilt your engine? Did you rebuild your heads or have the valve guide play checked? If those are worn you could also have oil pass there as well.
Check the inside of your air cleaner and intake for oil too, you could have a bad breather assy. which is staying open allowing oil to get by.
Worse case, blown head gasket or cracked head :(
 

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X2! That is what I meant to say!! LOL Valve guides seals!!
 

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Discussion Starter · #5 ·
Thanks folks! No I didn't change the valve guides when I changed the piston ring and head gasket. I was wondering if that might be the issue. I'll check the intake for oil from the breather. I did change that (what a PIA as it's under the flywheel) Are the valve guides difficult to replace? do i need any special tools? I was planning to take the head offf to see if it was a head gasket. If I do that I guess i might as well change the guides.
 

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Whether or not it has a fuel pump is not really the engine, its more the tractor. Where is the fuel tank on the tractor? If its under the hood, its gravity feed, which is likely. If its under the seat, it has a fuel pump.

Definitely check the valve guides.
 

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Did you hone the cylinder when re-ringing..? If not, and all other conditions check ok..then you may have polished shiny cylinder walls that won'y allow your new rings to "seat"...disreguard this idea if you do have a decent hone pattern...Just thought its worth mentioning if youre going to pull the head..
 

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Discussion Starter · #9 ·
The fuel tank is right behind the engine and is gravity fed. When I rebuilt the engine the cylinder wall looked fine. Still had the hone pattern on it.
Now that I'm into lawn season here is the exact pattern I get. When I start it up it's fine for about 15 seconds. Then it slowly starts to blow smoke until it reaches full smoking in about 5-10 seconds. It will then blow this smoke for a good minute and then taper off to nothing noticeable. I've gotten to starting it and then walking away for a few minutes until the air clears but I can image what the neighbors must think.
anyway enough of the responses seem to point to the valve guides so that's where I'm headed. I already got them from B&S along with a new head gasket and valves just in case.
 

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Re-thinking ...you say it's fine [no smoke] for first 15 seconds of cold start..I don;t beleive that is a condition of worn valve guides...as I beleive they would allow slow drip over time when sitting, cylinder would be oil wet at first start..and definately smoke imediately , But I could be wrong...as there may not be enuf oil up top to drip in..[compared to car engines that I'm thinking of]..Let us know if the new guides do cure it, certainly less work than having to go for the rings again..thou I'm focusing on a problem with the new rings, maybe end gap not staggered..But Hope I'm wrong.
 

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Discussion Starter · #11 ·
Just wanted to close this out with an update. After all the snow from this miserable winter finally melted and I was able to get to my shed I pulled the head off the engine. Changed the intake valve guide, which has a rubber type seal around it. The exhaust guide, which is all metal due to the heat I'm guessing, looked ok and measured within tolerance. Put new valves in for the heck of it as well as new head gasket. Put it back together, started it up and what do you know, no smoke! So exciting when something actually gets fixed. Thanks for everyone's input. Another great forum for the do it yourself-er.:2th:
 
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