Posted by George Marsh on October 16, 2012 at 14:30:00 from (220.127.116.11):
In Reply to: Re: GX390? posted by Billy Shafer on October 16, 2012 at 07:50:42:
Billy, Checked valve clearance. Both were close. Tightened the exhaust perhaps .001-.002 inches. Nothing major. However, I did notice what Honda called using the exhaust valve as a decompression valve. When I rolled the motor over slowly, the intake valve open and closed. On the compression stroke, the exhaust valve opened a small amount and just breifly. Then on the exhaust stroke, the exhaust valve opened even more and stayed open for a longer time.
How does Honda do this? I'm guessing it has 2 lobs on the exhaust cam. Or is there another way to get the exhaust valve to open briefly on the compression stroke just while you are starting the engine? Wouldn't this send a small amount of fuel/air mix out the exhaust before there is a spark?
Do other small engines do the same thing making it very critical to keep the exhaust valve clearance spot on the money?
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