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B & S 42A707 oil splatter from exhaust


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12-22-09, 07:15 PM   #1  
B & S 42A707 oil splatter from exhaust

I got an old MTD rider given to me and rebuilt the carburetor and got it running. It was running good and I mowed a couple of days with it. The third day of mowing it lost power and I noticed oil splattered around the exhaust. I think it's blowing out of the exhaust from one cylinder. It still runs but runs real rough. It seems like the one cylinder that appears to be blowing oil out the exhaust doesn't run right. Any ideas what might be causing this? It's a B & S 18.5 hp twin cylinder Model 42A707 2238E1 970 9195A

 
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12-22-09, 08:55 PM   #2  
Check the oil level. Is it too full? Is it thin and smells like gas?


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12-22-09, 10:17 PM   #3  
The oil level is fine and it looks OK. It doesn't smell like gas. I checked the consistency with 2 other riding mowers I have and it looked the same.
It was starting real easy before. Didn't have to choke it and it fired right up. Now it has a real difficult time even turning over.

 
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12-23-09, 12:32 PM   #4  
I also notice a slight whistling noise when the engine is turning over. It sounds like air escaping somewhere in the engine. Could this be a compression leak somewhere in the engine?

 
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12-23-09, 10:34 PM   #5  
Remove the spark plugs and check for compression on both cylinders.


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12-24-09, 08:53 AM   #6  
How much compression should I be looking for? What numbers?

 
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12-24-09, 06:58 PM   #7  
Anything at all at this point. 90 psi and up is ideal, but I'm thinking this is a matter of some compression or none, not how much.


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12-27-09, 06:46 PM   #8  
OK. I finished all the Christmas celebration and have gotten back to the engine. I checked the compression and I'm not getting any reading on either cylinder, but it still runs. What am I doing wrong?
I started it and pulled the plug wire on one cylinder and got no change. I replaced that wire, then pulled the wire on the other plug and the engine died.

 
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12-28-09, 12:21 AM   #9  
That means the one cylinder that made no change is not producing power. You may have a bad compression gauge. Put your finger over the spark plug hole and see if it has compression on that cylinder. If not, put a pencil into the plug hole and turn the engine by hand. If you do not feel the pencil moving up/down with the piston, it has a broken rod which is what I have suspected.


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12-28-09, 07:06 AM   #10  
I pulled the cylinder head off yesterday and turned the engine over. The piston and valves all seemed to function fine.

 
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12-28-09, 10:24 AM   #11  
Pulled the head off? Did you check piston movement or to see if the spark plug is firing on that side before tearing it down?


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12-28-09, 10:59 AM   #12  
Yes, it was firing. I cleaned the head and valves and put it back together. I started it and it ran good and I thought everything was OK. I gave it some throttle and it responded well, so I idled it back down and let it idle for a few minutes. After 3 or 4 minutes of idling, it began to sputter and died.
When I tried to start it again, it just barely ran like before.

 
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12-28-09, 06:26 PM   #13  
If one side is skipping, it is either not getting spark, compression, or air/fuel mix. If it has spark (check when it is not running right, since spark can come and go at times if the coil fails in a particular manner). If it is sparking, then check compression when it's messing up (compression can also come and go if a valve is sticking or a valve seat is loose). If both check out good, then go for the carburetor. It could have a piece of trash floating around in the bowl blocking a jet sometimes, and sometimes not.


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12-28-09, 09:11 PM   #14  
I did find the oil leak that I thought was coming from the exhaust. It was leaking at the valve cover. Bad gasket. Could a bad valve breather gasket cause all this trouble?

 
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12-29-09, 07:52 PM   #15  
I never could get a compression gauge to give me a reading so I reversed the process and pumped compressed air into the engine. I turned the crankshaft until both valves were closed and pressured a cylinder. I could hear some air escaping through the carb, but one cylinder leaked down at the same rate as a 13 hp B & S engine I have that runs real good. The other cylinder would not build up more than 50 lbs of pressure as the air escaped through the carb too fast. Does this mean the intake valve or valve seat is bad?

 
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12-31-09, 05:27 PM   #16  
Sounds like the intake valve is not seating for some reason. I'd pull the head back off and have another look.


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12-31-09, 10:27 PM   #17  
I did just that. Cleaned the head, piston, and valves with Sea foam. I put it back together and it started right up. It has full power, starts easy, idles good, and responds well to the throttle and when the PTO is engaged. It's running good. Thanks for the help.

 
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01-01-10, 03:57 PM   #18  
Glad you got it. I figure there must have been some carbon or something interfering with either valve movement or the seating surface of the valve.


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