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valve adjustment question


sdodder's Avatar
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10-01-15, 07:43 AM   #1  
valve adjustment question

Hi, I've seen instructions on how to set the crankshaft position for valve adjustment
and I have a question: when 1/4 inch past TDC is specified, is this a measurement
of piston travel, or a distance around the flywheel, or crankshaft pulley? I'm assuming this is to get past the compression release, right? This is on a B&S 16hp Vanguard V twin. Any clarification would be appreciated. Steve

 
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marbobj's Avatar
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10-01-15, 08:35 AM   #2  
It's to get past the compression release - correct. TDC is the piston position in the cylinder and the reference mark is on the flywheel. Piston travel is expressed in terms of inches or metrics and the flywheel rotation is stated in terms of degrees.

 
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10-01-15, 08:42 AM   #3  
I use a thin screwdriver in the spark plug hole. Have a good one. Geo

 
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10-01-15, 11:47 AM   #4  
AFAIK, it would be the crankshaft pulley. I would think that the valves should be closed before TDC As the intake valve on the opposite cylinder starts to open, you'll feel the compression load as you turn the engine, by hand. I was taught to adjust valves when the compression loads.

There is a youtube video that does it using yet another method. They open the exhaust valve all the way & adjust the intake valve on the same cylinder to .004". Then they do the same with the intake valve opened, all the way. The same method is repeated, on the other cylinder.

 
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10-01-15, 04:44 PM   #5  
You do it with the piston 1/4" down from TDC, measuring the actual piston travel, not the flywheel or crankshaft. Don't do it with one valve open and then the other valve open. Valve adjustment is critical on these for more reasons than the obvious. You can get these close enough to start and run with sloppy adjustments but if there is too much clearance, you risk ruining the camshaft. What happens with the soft lobes on the newer camshafts that aren't cast iron, the cam lobe comes around and slaps the lifter over and over until it wears marks in the lifter and then the cam lobe wears off to a round circle in short order. Keeping the clearance within specs eliminates this "slapping" action and saves the cam.


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sdodder's Avatar
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10-02-15, 04:33 PM   #6  
valve adjustment

Thanks for all the reply's. I appreciate the information, and love the accumulated knowledge on this message board. I'm sure I'm not the only one that reads these posts almost daily. Sharing this kind of knowledge is what makes this message board great! Thanks, Steve

 
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