Here is a web site that gives a complete, technical, professional
description of doing a differential compression check on an aircraft
engine. If you ever want to understand the what's, the why's, the
wherefores of compression testing on any gasoline (don't know how this
applies to diesels) engine, then this is a very worthwhile read. Flat,
opposed cylinder aircraft engines are not that much different from
aircooled or WBX watercooled engines, so the principles apply.

The Differential Compression Test is more accurate that the standard
automotive test, and it is worth knowing how to do, and to do it.

http://www.amtonline.com/publication/article.jsp?pubId=1&id=2234

Regards,

John Rodgers
88 GL Driver
Chelsea, AL

Geza Polony wrote:
> John,
>
> What I'm reading from this person's description is basically that you pump
> air into the spark plug holes and listen where it comes out--exhaust,
> intake, or coolant. Why do you need even to measure the pressure? Are there
> some specs to measure against, eg., each cylinder should hold x amount of
> pressure for x seconds? If so, what are the specs? I've never done one of
> these tests before.
>
> Thanks,
>
>
> Geza
>
>
>