Compression Test - How To

[Bdogridgeback]

Hey Guys
Just bought an 05 ridgeback and was going to check the compression but wasn't sure if I needed to ground the plugs or disconnect the coils. Can anybody guide me here where I don't fry anything?
Also what pressures are good between the two cylinders.
Thanks for the help !
Lp

 

[Sven]

Book approach vs. NOLTT is the day I walk out to the vehicle is the day it won't start. Has fuel, has spark, only thing left is compression. I run a cold number as if waking out to take a ride and that day is more or less room temp. Book suggestion is to warm bike, then take a compression test hot. This shows parts expanded, tighter seal, and then a new number to digest. Your choice.

Charge battery before test, then charge after test>> if using starter. That, or forgo moving the spark away from the plug holes [if kill also kills the starter motor], find 6th gear, run that bike up the street till the needle stops... no charging needed; just a paramedic.

The two thoughts in pounds are; a 10% or 15% difference between cylinders is within [so-so] specs, so a closer pulse difference would be the 10% difference. If the pounds are 100 psi and the other cylinder is 115 psi, think the lower number as the problem child.

 

[john sachs]

Simple method:
Cold Cranking Compression Check. Both spark plugs removed from heads, installed in wires, and resting on an engine metal part(grounded).
1- Fully charged battery. Disconnect compression releases.
2- Screw gauge in cylinder. Open throttle all the way.
3- Crank engine until the gauge stops moving. Record number.
4- Next cylinder- repeat like the first.
5- If more than 10-15 lb. difference, low cylinder could be a problem.(do leakdown test next).
John

 

[Bdogridgeback]

Thanks guys, what do I need to look for in disconnecting the releases?
The bike has had a new hard wired harness installed I was told due to previous issues.
Thanks guys
Lp

 

[Mr. Wright]

If you can't find the plug to disconnect the compression relieses, run a jumper wire from the battery to the start solinoid, thins will spin the engine without inguaging the solinoids

 

[john sachs]

If you can't find the plug to disconnect the compression relieses, run a jumper wire from the battery to the start solinoid, thins will spin the engine without inguaging the solinoids

Leave the ignition switch OFF when jumping the solenoid.
John

 

[Bdogridgeback]

Jumped the starter since the releases were hardwired, running about 185 front and rear cylinders cold , throttle open with a snapon guage. Does that sound about right ?
I tried a harbor freight guage and it was reading about 140 on both.
Thanks guys