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Cub Motor Knock?

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#1 Justin2655 OFFLINE  

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Posted May 31, 2013 - 10:16 PM

I have a cub 102 with the 10hp kohler, it's been setting for quite some time as we took the carb apart it was totally junk, not worth saving or any chance of anything, I had a spare around to throw on so covered that problem. When you turn the motor over it sounds as if it has quite a bit of a knock/slop back and forth. But when I started it. It actually ran very well, then all of a sudden outta no where a horrific knock started for about 10 seconds, then quite, throttled it up some, ran smooth and then it happend again, I don't get it, I've never heard a motor do that, what would my problem possibly be? It sounds like it knocks real hard and runs like crapper and then it runs fine, no knock or smoke at all

#2 superaben OFFLINE  

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Posted June 01, 2013 - 07:20 AM

Knocks can come from all over the place on an old engine. 


Have you checked the flywheel?  Is it on securely?  I'd start there.  That's the main thing I can think of for a knock that comes and goes... that's really unusual.  Usually a knock comes and is "here to stay." 


If it rocks freely back and forth a little bit while you turning it by hand while its not running, then I'm worried that the connecting rod is toast.  Pull the engine head and hold down the piston while rocking the flywheel back and forth. If you feel the piston move with the rocking, then everything is probably in decent shape (although if I was you I would still pull it off the oil pan and check it over).  However, connecting rods on Kohlers are usually pretty hardy critters unless someone abused it.


Otherwise, there is a probably a bearing out.  However, I would think you would hear that all the time!


Ben W.

#3 motobreeder OFFLINE  



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Posted June 01, 2013 - 08:35 AM

I'm interested in this discussion.  I have a motor that only knocks at various RPMs and only when warmed up.


I still need to make sure the knock isn't coming from something connected to the motor - PTO clutch or drive shaft.

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Posted June 01, 2013 - 09:02 AM

I have a 147 that had been sitting, and starting knocking when I started it again. An oldtimer told me that it could be a points problem and not an internal engine problem. I still haven,t checked it out yet, though.

#5 Grumpy OFFLINE  



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Posted June 01, 2013 - 02:22 PM

I would pull the head look for carbon build up,  or maybe a screw out of the old carb.

#6 EricFromPa OFFLINE  



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Posted June 06, 2013 - 08:29 PM

I bet the cylinder is egg shaped.Piston slap sounds almost identical to a rod knock.But with a rod knock it will do it all of the time.

It will knock worse if the spark timing is off or if the Cam lobes are worn.