Comp. Test Procedure....Any Consensus ?

best way is firstly to make sure the car has had a run and is running as well as it can be. Performing a comp test on a car that's sat around for 6 months or so is meaningless really (especially dirty old carb cars).

So, if it runs ok, drive it for 30 minutes to "clear" it out.

Then, disable the ignition by grounding the points wires.

Disable the fuel pump by pulling the fuse or pump wire.

Remove all the plugs (put them down in order of where they were removed).

Open the throttle wide, and trap it open with a wedge of some kind (Dont pump a carb car).

Make sure the battery is healthy, and starter turns consistently. Use jump leads if in doubt.

Connect the comp tester and spin the engine equally for each cylinder. usually 8-10 compression beats is enough to observe no further rise in the pressure.

Then, to learn more about the engine, do a leakage test. need another tool for this.

 

usally i just remove the coil wires from the coils. the ones that go to the dist.that way no spark will go to the dist. when you remove the spark plugs examine them closely. they will tell you alot about your motor. take your time and good luck.

 

Excepting that on a Ferrari, the coil leads are fastened inside the distributor cap. Although I suppose you could use spare coil wires to ground the coil, it may be safer on all concerned ( like me ) to simply disable it. If you simply removed the coil wires from the coil, the coil could still jump spark from the tower to the ground lead, burning a carbon track into the coil, among other maladies. I dont think that was meant, but I just want others to be aware of that potential damage.

I have been electrocuted by an ignition system, and I will tell you it is one horrible experience. A "friend" decided to start a V8 engine I was working on, while I had three spark plug wires in my hand I had just pulled off. I could not let go, and until he shut the car off, I got probably close to a hundred good shocks in a few seconds time while I danced aroung herky jerky, feeling ZAP ZAP pause ZAP pause ZAP ZAP pause, in a rapid reapeating pattern. Actually it was #1, #3, pause, #5, pause......Luckily it was an old point style ignition and not some newer CDI type, or I may not be here to tell of it. Needless to say I am rather paranoid of ignition systems, and sometimes feel shocks mark you in some way, so that you become some kind of human lightening rod, easily zapped while someone closer to it remains unscathed. Not unlike spider bites.

 

No worries Brettski. I actually gain out of it... hopefully... people will put questions on here, rather than email or phone me up for free consultation while I'm trying to earn a living duruing the day.

On a points/carb car, you don't really have to diable ign and fuel if you dont want... it's just proper practice to, thats all.

Grounding the little points wire, either at the coil Neg or dist body will suffice. Simply pulling the Col HT lead out will cause it to arc and crack around...potentially dangerous.

 

On further recollection, it was 5,7, then 3, then 5,7, then 3. repeat as necessary. God, I been thinking of that all day. In 5 seconds with the engine turning 500 rpm, I would have been bit almost 90 times.

 

Krowbar:
I liked your little story it reminded me of getting zapped myself! ;-)

Glad you clarified the firing order.

Mark

 

I got zapped by a BB once... explains a lot of things ....CDI system to the brain!