Re: Valve tap-or rod knock?


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Posted by casebro on Friday, October 04, 2002 at 7:56PM :

In Reply to: Valve tap posted by Joey on Friday, October 04, 2002 at 5:14PM :

Diagnosis method #1:
Cylinder balance test:
After it's warmed up,try disconnecting one spark plug wire at a time- at the distributor so you don't get zapped. All cyls should drop speed equally. If the knock goes away on one cyl, you've got a rod knock,(it's most often #6.

Diagnosis Method #2
Localize the noise:
Using a long rod, long extension, or a mechanic's stethoscope, listen at the low edge of block, lifter covers, & cylinder head for where the noise is loudest. If it is the head, your rod is so worn it allows the piston to strike the head.

Note, a compression test won't help locate any problem but burned valves or bad head gasket, both of which can be diagnosed quicker with a cylinder balance test (see #1 above), then use compression test to verify.



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