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Posted by Chriscase [76.201.18.183] on Wednesday, February 17, 2010 at 14:49:50 :
In Reply to: Cracked piston posted by Robert N [70.184.66.179] on Wednesday, February 17, 2010 at 11:52:29 :
Back to teh basic knock test:
rev slightly, until you get max noise. Now try disconnecting plug wires at the dist. If no change, try it at a different speed. You may find a spot that gets quiet when disconnecting a plug wire, or you may find a spot that makes more noise when the wire is unhooked.
The knock can come from two places. A loose bearing may knock at the crank.
A very loose bearing may allow the piston to hit the head. This may be dampened by the air in the cylinder, or the pressure of the combustion. This may break the piston, since it hits only to one side. Low throttle means less air to dampen the piston's motion. Lots of throttle will load the piston with a bigger power surge.
All these noises vary with speed, throttle, or load. Is there one spot of rpms where the noise is worst? Or better? Try pulling plug wires in both places.
Are you sure it isn't just pinging? Usually sounds like a jingling noise.
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