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15.5 OHV Briggs knocking at idle


e40's Avatar
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12-02-06, 06:57 PM   #1  
15.5 OHV Briggs knocking at idle

My very lightly used Craftsman mower with the 15.5 Briggs motor seems to be knocking at idle. It sounds like it's coming from the back side (bottom end) of the block. Once I increase the RPM, or apply a load such as the snowblower attachment, the knock goes away. Any ideas? TIA

 
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v8driver's Avatar
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12-02-06, 07:35 PM   #2  
are the mounting bolts (what holds the engine onto the frame) tight? and I mean very tight....

 
e40's Avatar
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12-02-06, 07:43 PM   #3  
They seem to be. I don't see any physical movement either.

I was just on the Briggs site and they said to check the flywheel, and pull the head and clean out the carbon. So I'll give that a shot and see what happens. (fingers crossed!)

 
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12-02-06, 08:09 PM   #4  
I have a 3.8hp techumse verticle shaft engine that did the same. It was my grandmas mower and it got so bad Ididnt want to use it but she said mow my yard. Anyways it got worse and finaly had no compression. I took it apart and the oil pump is plastic and cracked. I super glued it together and its been running for about 4 years now. It still knocks for a few seconds when I fire it up in the spring but runs like a top.

 
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12-02-06, 08:42 PM   #5  
Check the engine mounting bolts and the PTO pulley bolt to be sure all are very tight.


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v8driver's Avatar
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12-03-06, 09:21 PM   #6  
You won't really see the engine move much when running, or be able to move the engine much by hand back and fourth when not...
They must be very tight... or it will cause a knock noise at idle and usually clear up at speed (the bolts are bumping around in the frame mounting hole)

 
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