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Good Afternoon All,

Can anyone tell me what the normal cylinder compression is for a 327 straight 8. My son overheat my Patrician this summer. I've changed the head gasket, new spark plugs, new hoses, new thermostat, new coil, etc. The car will not start. I did a compression check and I got 30-40 psi on each cylinder. This seems really low to me. Any information will be greatly appreciated.

Ramon

That is really low. My 327 by comparison is around 118-122 per cylinder. Something is really wrong if you are getting 30-40 across every cylinder. How are you taking the measurement?

Maybe not holding the throttle open all the way to allow air in? I know that always makes a big difference on my readings. I have a bike with 130 PSI with an open throttle and 60 with it closed. Didn't do it right the first time and i was so worried i was in for a rebuild before i found out i had to open the throttle blades so it could get air in. *duh*!

30 - 40 psi is VERY low. Try some starting fluid.
Did u squirt oil into the cylinders before checking compression???? That is important as well as holding throttle open.

In nearly all engines, compression much below 70 psi will cause difficulty in cold start and some difficulty to a lesser degree at hot start.

The 30 - 40 psi is really not acceptable.

*Duh* is right. I was cycling the motor from under the hood while holding the compression gauge. It sounds like I need to get my lazy son out there to depress the gas pedal while I take the readings. As always, thanks for the great advice. Will post my results as soon as I re-test the compression. Ramon

This may be too elementary, but when I check compression this is how I do it.

Remove air cleaner

Remove all spark plugs

Ground distributor primary wire (the small one from the coil to the distributor.

Hold throttle wide open, and on a cold engine make sure choke butterfly is fully open too. Generally, compression tests are done on a warm engine, but a cold engine can be tested too.

Insert/install compression gauge securely into spark plug hole, and crank engine at least four cycles until highest reading is obtained on gauge. Gauge reading should increase with each cycle.

Note reading.

Repeat for remaining cylinders.

Look for differences of more than 20% and large differences between adjacent cylinders.

This is for a "dry" test.

For a "wet" test squirt some engine oil into the cylinder and crank the engine without the gauge installed; then repeat the procedure as in the "dry" test.

Compression reading increase over "dry" test is a sign of worn piston rings.

As I said at the beginning this may be too elementary for most, but it bears repeating from time to time.

(o{I}o)

Thanks JW, it's never too elementary for me. Thanks for the suggestion. I got the car started! I'm still gonna do the compression test as suggested, just for my own peace of mind. Thanks to all for the advice. Ramon