Compression Test

[Frank]

Good Evening
Could you please advise the procedure for carrying out a compression test on the stag engine
Many Thanks
Frank

[Lingen]

Frank.
When I do it, I warm the engine a little bit, then disconnect the +ve lead to the coil. Then remove all the sparking plugs and test the cylinders one by one with the accelerator pedal depressed. The pressure should built to the maximum in around 6 compression strokes. Don't forget to replace the coil lead!
Mike.

[Frank]

Thanks Mike
Could you just confirm you remove all eight spark plugs or just four (one bank)at a time
Regards
Frank

[sujitroy]

remove all

[Lingen]

Frank.
As Sujit says, remove them all, which will allow the engine to turn over more freely. Not essential, but kinder on the starter motor.

[sujitroy]

Mike. Why depress the accelerator

[JeffW]

Frank.
When I do it, I warm the engine a little bit, then disconnect the +ve lead to the coil. Then remove all the sparking plugs and test the cylinders one by one with the accelerator pedal depressed. The pressure should built to the maximum in around 6 compression strokes. Don't forget to replace the coil lead!
Mike.

+1

[wilf]

Mike. Why depress the accelerator

To allow the engine to breathe fully, and stop inlet vacuum from corrupting the compression readings.

Also it establishes a "standard" way to compare readings across engines.

[Lingen]

Sujit.
See Wilf's reply!
Mike.

[sujitroy]

Thanks. Aren't the butterflies in the carbs slightly open enough?

[wilf]

No. If they were, you would not have plenum vacuum at idle.

[garyf]

I know I'm going to make myself look even thicker than usual but I've always wondered what 'depressed' means
foot on accelerator or foot off accelerator?
I genuinely don't know lol

[wilf]

Foot on i.e. wide open throttle.

[Lingen]

It also has a Covid-related meaning. No wonder English is such a difficult language for others to learn!
Mike.