Bent exhaust valve

jlloyd_B&S

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I have a Craftsman Snow Thrower with an 8 HP engine (12E114-0268-E1) After using it a few weeks ago when it ran fine, I let it cool and placed a tarp over it. All snow was cleaned off the thrower. A week later I tried to start it on a cold day below freezing and it seemed locked up. I continued to try and broke the rope starter pawls. I used the electric starter with no luck. I waited until we had a day above freezing. I could get the engine spinning using the electric starter but it would not fire. Lots of backfiring and compression lock up. I disassembled almost everything and checked out the function. carb and spark seemed OK. I removed the exhaust and to my surprise found a lot of water in the muffler housing and in the cylinder head around the exhaust valve. There was at least three tablespoons total. I dumped it out and blew out the exhaust port. There was no water in the crankcase. I then removed the valve cover and discovered a bent exhaust valve push rod. My theory is I bent it when I tried to start the engine in freezing temperature and ice from the water accumulated had frozen the exhaust valve in place. As a trial I put the good intake push rod into the exhaust valve guide and it seemed to function properly. So... can I expect to be able to get the engine running again by replacing the exhaust push rod only? What is likelihood that the bent rod is the only damage? Anyone know why water in this large quantity collected in the exhaust port after I stopped the engine when it was hot? Seems like normal condensation would not explain all this water.
 

ILENGINE

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Replacing the push rod should be fine. I suspect that water condensed on the underside of the tarp during the day and dripped into the exhaust then at night it would freeze.
 

jlloyd_B&S

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Thanks for the response. Exhaust port that collected water was shielded by the muffler. Condensation must have been inside the muffler but it seemed unbelievably wet for it to be just condensation. Unlikely that snow was ingested as the muffler was hot when I stopped and I covered after it cooled in blue sky weather. Last winter the same thing happened (water in exhaust port) but I did not break anything. I received repair parts a few days ago and tomorrow looks like a nice day to see what I can do to get the snow thrower back working and, hopefully, ready for seasonal storage.
Jim
 

jlloyd_B&S

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Update: I replaced the bent push rod today with a new part. I attempted to adjust the valve lash and discovered I could not loosen the locking set screws on either rocker adjuster. I was able to loosen the entire rocker arm adjuster. I set the lash by turning the entire adjuster. (My book said 0.004-0.006 on the intake and 0.009-0.011 on the exhaust). I set to .005 (I) and .009 (E) respectively. Are those specs right? YouTube videos for setting lash on B&S lawn tractors seem to set both valves at .005. My operator's manual (OM) specified the wrong spark plug also so I am not confident in the OM. I felt that allowing the exhaust valve to be open a little more might not allow it to cool enough or will it allow it to cool more? I reassembled all the pieces and turned the engine over with the electric starter and it started instantly and ran strong. I have fixed the push rod problem but I am not sure the lash settings are going to hold. Are the set screws possibly locked with Loctite or something requiring a little heat to loosen? If so, I will need to go back in and fix that problem.
 

ILENGINE

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I have never seen loctite on the valve adjustment nuts. I have had to hold the adjustment nut and then break the set screw loose. they can be a pain sometimes to break loose.
 

jlloyd_B&S

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Thanks for that feedback. I exerted quite a bit of torque... more than I thought should work... on trying to break them free. The hex wrench was bending a little and still they would not budge. I was afraid of rounding out the socket so I left them the way they were and set the lash without using the locking feature. They were likely out of adjustment so it is better than it was but how long will that last? I will go back in and exert some additional force and maybe some heat to see what happens. I would have expected one of the two to move but neither one did. I guess the worst case is I will need to order new rocker adjustment assemblies. Luckily it will be 80 degrees today so no chance for snow until probably next December. I have had this machine since new in 2004 and this is the first time I have fooled with the valve lash.
 

BlazNT

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They will last till you start and run the mower.
 

jlloyd_B&S

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I just removed the valve cover and tried to loosen the set screws on the rocker adjusters again. No movement with reasonable application of torque. I got my heat gun out and applied it for a few minutes on high. In a few minutes the set screws loosened and I was able to remove each of them easily. There was definitely some kind of yellow lock fluid used on them and probably from the factory. It looked like the heavy duty stuff used by GM on its brake caliper mounting bolts. You need liberal heat to loosen it up. After they cool down I will set the lash again and lock them down the conventional way. I have used the blower for 10 years and it was lacking a little power this year so maybe that yellow lock fluid did keep it reasonably set for a decade without resetting the lash.
 

BlazNT

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I'm glad you got it figured out.
 

jlloyd_B&S

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Thanks. I also rebuilt the recoil starter mechanism with new pawls and a new spring and have everything all pieces and parts back in original positions with no parts left over. Engine starts and runs strong. Ready now to put it away for the season. I still have no real good theory for why so much water collects in the muffler and exhaust. It is a tough place for water to enter and collect as the exhaust port is completely shrouded by the muffler which goes up vertically and then runs horizontally. Oh, well. It has to be condensation but that is hard to believe unless a vandal runs around squirting water into exhaust ports! Not likely.
 
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