# Bad Test Equipment



## MariettaMike (Jun 14, 2012)

For no particular reason I picked up a free rental compression tester at AutoZone while I was there for some other stuff on Thursday. Pulled plugs, put the tester on top, gave it a spin. EIGHTY! middle SEVENTY-FIVE! bottom SEVENTY-SEVEN

After 48 anxious hours I tested it again with a different gauge at the Yamaha dealer and found 118T-110M-118B

Lesson Learned: Don't trust free diagnostic test equipment from a place that only sells parts.


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## cutrunner (Jun 8, 2010)

There wasnt really anything wrong with the guage technically. Im sure it was very used and probably dropped a few times.... but it still gave readings within 10percent of each other. Also EVERY guage is different, and ive proven that to my snap on guy by taking 2 brand new guages off his shelf and testing the same motor back to back.
also you need to be checking your compression on a warm, just ran motor for more accurate results


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## priscillatgorilla (Nov 29, 2014)

> There wasnt really anything wrong with the guage technically. Im sure it was very used and probably dropped a few times....  but it still gave readings within 10percent of each other. Also EVERY guage is different, and ive proven that to my snap on guy by taking 2 brand new guages off his shelf and testing the same motor back to back.
> also you need to be checking your compression on a warm, just ran motor for more accurate results




true !

you're looking for uniformity - "specs" are often misleading


compression tester results will vary


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