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Timmy-Boy 11-15-2012 09:26 PM

Compression Test?
 
I was wondering how I could do a compression test on my 1972 skylark. It has a 350 with a 2bbl carb. I was also wondering If there's any other engine tests I could run. Since I just bought the car. It runs great and all but I just wanna check on whats going on In there.

gearheadslife 11-15-2012 10:21 PM


techinspector1 11-15-2012 10:39 PM

Quote:

Originally Posted by Timmy-Boy (Post 1611804)
I was wondering how I could do a compression test on my 1972 skylark. It has a 350 with a 2bbl carb. I was also wondering If there's any other engine tests I could run. Since I just bought the car. It runs great and all but I just wanna check on whats going on In there.

Cylinders are numbered the same as a small block Chevy, from the front on the driver's side and going toward the firewall, 1-3-5-7. From the front on the passenger side and going toward the firewall, 2-4-6-8. Firing order is the same also, 1-8-4-3-6-5-7-2.

First, use tape and a magic marker or Sharpie or other indelible ink pen. Tear off a 4" piece of tape and wrap it around the spark plug wire right next to the boot where the boot pushes onto the spark plug. Mark each tape with the cylinder number as you pull the boots off all the spark plugs so you will get the correct wire back on the correct plug.

Remove the air cleaner and use a piece of wire or heavy string to hold the primary throttle blades wide open so the motor can breathe.

Find the + (positive) terminal on the ignition coil, remove the nut and remove the wire, wrapping the end of the wire with tape to prevent arcing against metal in the presence of the combustible mixture being pumped out of the spark plug holes as you rotate the motor with the starter.

Remove all the spark plugs so the motor will turn over easily.

Thread the hollow adapter into the spark plug hole, hook up the hose to the gauge and have your buddy turn the starter while you monitor the gauge. Let him stay on the starter until you get enough "chuffs" on the gauge to top out the needle so it won't go any higher, usually 3 or 4 "chuffs".

Write down the pressure you found, listing the cylinder number and move on to the next cylinder.

Post your findings on this thread.

I see gearheadslife got there before me. Thanks. I started my reply, then got interrupted.

cobalt327 11-15-2012 10:58 PM

Another test you can do is a vacuum test. You want to use an undamped 'diagnostic' type vacuum gauge. Use the info here to interpret the readings.

On a stock engine, often setting up the distributor's mechanical advance can help, along w/adding some initial timing. This can depend on how much compression the engine has, along w/the quality of the gas you're using. The idea is to give the engine as much timing as it can use, w/o causing it to detonate. More on that here. You'll notice the page was originally on the GM HEI (which could be a good swap for you to make), but the timing advance info still applies.

Good luck.


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