Knock,knock,knock

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  #1  
Old 11-19-03, 12:28 PM
needles
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Knock,knock,knock

I just rebuilt a Briggs 12 hp I/C engine. I got it when it was siezed,it was run with no oil by the previous owner. I got it unsiezed,polished up the crank,cleaned up piston,everything put to factory specs. I got a connecting rod out of the same exact engine that I had,the rod was mint,so I used it,it matched up to everything on the piston and was identical to the old rod,that was gouged to hell. After everything,mouted it on the tractor,ran it,and was happy that it ran,but at high RPMs,it has the worst knock I've ever heard,low RPMs is fine. The engine is running pretty strong,just that knock. Without ripping it all apart again,anybody have an idea what it might be? I'm leaning towards the connecting rod. Help me out.
 
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  #2  
Old 11-19-03, 02:09 PM
gmcfan
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Did you use plasigauge to check the clearance between the crank journal and the rod? When it siezed, the heat could have made journal out of round.
 
  #3  
Old 11-19-03, 02:21 PM
Terminator20's Avatar
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Good advice. Another thing you should check is your crank shaft and your piston rod. They may be bent. You never know, that might cause something nlike this too. Wait for Cheese to reply to this message before you do anything. He is the expert on engines.
 
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Old 11-19-03, 03:36 PM
needles
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Yes I did use plasiguage,the journal on the crank wasn't out of round,although it might of been. Terminator,on alot of your posts I've seen you usually post the obvious,easy solutions. If the rod and crank was bent I think I'd be able to tell. I'm probably going to have to rip the engine apart again anyways,I just posted to see if anybody had any ideas.
 
  #5  
Old 11-19-03, 06:24 PM
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Hi needles!

If the engine was run out of oil, I almost guarantee that the top journal for the counterweight is bad, and the bearing in the weight is bad. Did you check these? I had one a month or two that knocked like yours at high rpm. I wound up taking it apart probably 7 times or more trying to figure out why. The problem I found was a bent crank. It was not visibly bent, until it was chucked up and measured for runout. I pulled it out and smacked it with a hammer a few times in the journal areas to make sure I wouldn't mix it up with the other good cranks I had lying around.

Did you measure the crankshaft end play? If it is too much, you could possible get a knock at high RPMs.
 
  #6  
Old 11-20-03, 08:43 AM
needles
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Yes I did measure crank endplay,and it was to specs. Thanks cheese,I'll take that into consideration.
 
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