Compression Test ?

[RossL]

I have a decent compression tester I've used for years. Is there a special adapter needed to screw into the heads? It seemed very difficult to use what I have............... I couldn't seem to reach far enough to get the hose to thread into the head

What is the tread size for the spark plug openings?

[ward 57]

The compression testers I have ( why I have two I don't know ) but they both have conical rubber heads you just hold into the spark plug holes. No threading needed.

[MarkR]

the ones I ve used and the one I have now use an adapter. They need to screw in like a spark plug to be accurate.

[55blacktie]

Does your compression tester have 14mm threads or 18mm threads?

[MarkR]

Here’s the Maddox I used a few weeks ago. From Harbor Freight. That’s the extension with an 18mm fitting laying on the lid. I was calling the fitting an adaptor. It’s been a long few days.

[RossL]

My tester only has that size at the end of the hose and it doesn’t seem like the threads are deep enough to catch the threads on the head

I have to get a better adapter with longer reach

[MarkR]

Maybe this will help. Check the dimensions on the Maddox 18mm adaptor. You’ll need one this deep for a Y Block. Both hoses, the gauge hose and the extension hose, require an adaptor of the proper MM. Not sure about other brands but this Maddox gauge hose is too short for easy spark plug access. The extension makes for easy reach and you are able to turn it on the spark plug opening threads and then attach the gauge hose.
One note—make the adaptor to extension connection a bit more than hand tight and the adaptor to spark plug opening just snug by hand. That way you don’t leave the adaptor behind in the spark plug opening when you remove the assembly.

[RossL]

Harbor Freight kit had the correct adapter. Thank you to those that replied