compression test

K

kb3gup

Seaman Apprentice
Joined
Jul 9, 2007
Messages
47
Hello all,

I know when doing a compression test to pull the lanyard out so the ignition system isn?t firing, but won?t that still put raw fuel/oil into the cylinders? Then when you start it you run the risk of detonation?

Thanks

VJ60TLENE
92 60hp
 
D

daselbee

Commander
Joined
Jan 20, 2009
Messages
2,765
Re: compression test

First of all, remove all the spark plugs. This allows the engine to turn faster while you are doing the comp. test.

Pull that lanyard if you want.

You will notice that most of the fuel/oil charge is blown out of the open spark plug holes. I have never had one flood or "detonate" from a compression test.
 
5150abf

5150abf

Vice Admiral
Joined
Aug 12, 2007
Messages
5,808
Re: compression test

You want to pull the plugs and either pull the lanyard or make sure the plugs are grounded or you could damage the ignition, they need to either not spark or have soemwhere for the spark to go.

As far as extra fuel, no, that isn't a concern.

Detonation is when the gas charge iginites before the spark has gone off, with too much gas in the cylinder this can't happen.

You may be overthinking this one, nothing to worry about.
 
J

James R

Commander
Joined
Feb 1, 2007
Messages
2,664
Re: compression test

Remove from the cylinders and ground your plugs to allow them to spark. I use a simple piece of copper house ground wire fastened under one of the thermostat bolts. Coil the copper wire around the threads of each plug and away you go.
 
F

F_R

Supreme Mariner
Joined
Jul 7, 2006
Messages
28,195
Re: compression test

WARNING!!!! Allowing sparking whille cranking is a good way to start a fire. Ask me how I know....

Just lucky I wasn't standing in front of the plug holes!! I might not be here to write this!

Disable the ignition!!
 
tashasdaddy

tashasdaddy

Honorary Moderator Emeritus
Joined
Nov 11, 2005
Messages
51,019
Re: compression test

yea, but it shows you have great spark. had one cylinder blow fire once.
 
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