Compression
Thread Starter
Heel & Toe
Joined: Dec 2012
Posts: 20
Likes: 0
Compression
What is the average compression per cylinder for 1964 327 300 HP 10.5 compression? I am showing between 160 and 165. Showing oil deposits in 2 spark plugs. I believe the engine was rebuilt after removing the oil pan. Had balance numbers showing on the pistons and each rod and cap were stamped per cylinder. I removed the intake manifold. I had oil coming up through 2 bolts where the exhaust comes up to the carburetor. I believe someone used permtext on the ends of intake gaskets--walked away and then came back day or days later and installed the intake. Nothing was sealed in between. Do you have any suggestions?
Thanks
Thanks
Instructor
Joined: Aug 2001
Posts: 145
Likes: 1
From: Crown Point IN
Compression Check
Hey JW - Compression numbers are important, but so are the variances between highest and lowest readings. The best tool for evaluating an engine's overall health and determining the location of serious problems is a Leakdown Gauge. You remove the spark plug from a selected cylinder (make sure both valves are closed/engine is in compression stroke) and thread the tool into the spark plug opening. You apply compressed air into the cylinder and note the difference in air pressure on the twin gauges. A large discrepancy indicates the cylinder is losing too much pressure. Listen for the sound of air "whooshing" in the following areas:
Carburetor - positive sound indicates leaking intake valve
Exhaust pipe - positive sound indicates leaking exhaust valve
Oil filler tube - positive sound indicates leaking piston rings
If you get readings indicating leaking piston rings, that's a good sign that an engine overhaul is in order. I know that's not great news but it does save you a lot of money spent in other areas in a hopeless effort. The local speed shop also won't be able to sell you a bunch of "performance parts" that will have little impact.
Carburetor - positive sound indicates leaking intake valve
Exhaust pipe - positive sound indicates leaking exhaust valve
Oil filler tube - positive sound indicates leaking piston rings
If you get readings indicating leaking piston rings, that's a good sign that an engine overhaul is in order. I know that's not great news but it does save you a lot of money spent in other areas in a hopeless effort. The local speed shop also won't be able to sell you a bunch of "performance parts" that will have little impact.
Le Mans Master
Joined: Feb 2008
Posts: 6,463
Likes: 1,889
From: Folsom CA
I do not remember the factory spec for compression on the 300 HP 327. Having all 8 within 5 pounds is very good. Says rings and valves are all working equally well.
The cam in the engine will affect cranking compression, mild cam will give higher numbers than a performance cam. Less over lap and less compression bleed off.
The two plugs showing oil could be valve stem seals, not hard to change without pulling the heads. It sounds like you have a well built engine that was balanced. Stem seals are no big deal to fix. If stem seals are guilty you should have blue smoke on start up from those cylinders. Good Luck.
The cam in the engine will affect cranking compression, mild cam will give higher numbers than a performance cam. Less over lap and less compression bleed off.
The two plugs showing oil could be valve stem seals, not hard to change without pulling the heads. It sounds like you have a well built engine that was balanced. Stem seals are no big deal to fix. If stem seals are guilty you should have blue smoke on start up from those cylinders. Good Luck.
