Compression Test Adapter

I’m using the Denso Iridium plugs in my Lycoming O-390 and need to do a compression test. I would like to get an adapter for the tester rather than remove the threaded adaptor for the plugs. What size adapter do I order? Forgot to measure before I left the hanger and now I’m on a work trip. I think I need the 12mm adapter from spruce and would like to ke to get confirmation before I order. Any thoughts?

The pretty much universal thread for automotive sparkplugs is 14 X 1.25

Larry

Frankster13 said:

I’m using the Denso Iridium plugs and need to do a compression test. I would like to get an adapter for the tester rather than remove the threaded adaptor for the plugs. What size adapter do I order? Forgot to measure before I left the hanger and now I’m on a work trip. I think I need the 12mm adapter from spruce and would like to ke to get confirmation before I order. Any thoughts?

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You don’t mention what engine you’re doing the test on. I’ve been using the ATS adapter and it works great. Like Larry says, I think the one you need is 14mm. The 12mm would be for Rotax motors.