Might have time to do a Compression test today.
Thread Starter
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From: Just because I'm paranoid doesn't mean people aren't out to get me...
St. Jude Donor '09
Might have time to do a Compression test today.
I found this proceedure on line.
I'm going to perform the test on a cold engine. I'm not starting it again until I firgure out my problem. Should I perform it on all 8 cyl or only on the side where I'm blowing smoke?
What are normal readings for a BB? 60+
Any suggestion or tips welcome.
Screw the gauge into cylinder 1 and rest it somewhere you can see the dial while you crank the engine. Open the throttle fully either by pressing the accelerator or wedging the linkage open under the bonnet. If the throttle isn't open then air can't get into the cylinder and the readings will be far too low. Crank the engine until the gauge stops rising and count the revolutions while you do so. It should normally take no more than 10 engine revolutions (5 compression cycles) to get a full reading. You can count the cycles by watching the gauge too - each jump of the needle is one compression stroke. Write down the final reading and also make a mental note of how quickly the gauge rose on the first few cycles. Then just repeat for the other cylinders. Make sure that each cylinder reaches its highest reading after the same number of engine revolutions. If all readings are good then the test can end there. If any cylinders are low then a "wet" test can be done. This involves squirting a few ccs of oil into the cylinder and repeating the test. The oil will help seal bad rings and increase the reading but won't affect it if the problem lies in the valves or head gasket. Copyright David Baker and Puma Race Engines
What are normal readings for a BB? 60+
Any suggestion or tips welcome.
Safety Car
Joined: Oct 2000
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From: Carbondale Pa.
Hi, definately do all 8, both wet and dry to give you an idea of the overall condition,,,good vs. problem side. A lot more work involved but worth the effort to ease your mind. Peace,,,Craig 
Race Director
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From: Forked River NJ
Do all your cylinders. The overall number is not as important as what is the difference between cylinders. I would allow no more than 10% difference between cylinders with a new engine should be closer to 5%.
Thread Starter
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From: Just because I'm paranoid doesn't mean people aren't out to get me...
St. Jude Donor '09
Will all that cranking wear on my new battery? You think I should hook up my charger during the test as a precaution?
Thread Starter
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From: Just because I'm paranoid doesn't mean people aren't out to get me...
St. Jude Donor '09
Ok, what's our spark plug hole size? The compression tester has a 14mm threaded end but doesn't want to screw in and I don't want to FU my aluminum heads. Why metric? I bought it back in the early 80's as part of a set and it's never been used.
One step forward, two steps back.
One step forward, two steps back.
Team Owner
Joined: Sep 2003
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From: eville in
Originally Posted by Jughead
Will all that cranking wear on my new battery? You think I should hook up my charger during the test as a precaution?
keeps the numbers more even , then let us know
Melting Slicks
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St. Jude Donor '03,'11
Originally Posted by Jughead
Ok, what's our spark plug hole size? The compression tester has a 14mm threaded end but doesn't want to screw in and I don't want to FU my aluminum heads. Why metric? I bought it back in the early 80's as part of a set and it's never been used.
One step forward, two steps back.
One step forward, two steps back.
Make sure you take all the plugs out before you start.
you only need the comp tester hand tight. It has a big rubber o-ring to seal against.
I've done several searches on the internet. All spark plugs are coming up metric. You're ok.
Last edited by turtlevette; Oct 8, 2005 at 11:11 AM.
Burning Brakes
Joined: Apr 2004
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From: Des Allemands LA
Also remember to unhook the hot wire to coil so a loose plug wire doesn't arc put on something it isn't supposed to. Spark plugs are metric thread, sometimes it's a little difficult to get the tester started. As mentioned above, only habd tight is required due to the o-ring. It also helps protect the oring if you put a drop of oil on it before tightening-just keeps it from "grabbing" on the head.
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Thread Starter
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From: Just because I'm paranoid doesn't mean people aren't out to get me...
St. Jude Donor '09
What a major PIA!! 
I can't get the compression extesion into the spark plug hole because it won't clear the casting over flow on the exhaust manifold. There's excess on every hole! I'll have to grind the excess away before I can even get to screw in the compression tester. 
I can't get the compression extesion into the spark plug hole because it won't clear the casting over flow on the exhaust manifold. There's excess on every hole! I'll have to grind the excess away before I can even get to screw in the compression tester.
Le Mans Master
Joined: Jun 2002
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From: I can walk to MA
Is it a flexible hose ? I've seen flex extensions that might get you in there.
Good luck.
I seem to recall pressures up near or over 100psi, but as noted
above ... relative differences are more telling.
Good luck.
I seem to recall pressures up near or over 100psi, but as noted
above ... relative differences are more telling.
Thread Starter
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From: Just because I'm paranoid doesn't mean people aren't out to get me...
St. Jude Donor '09
Originally Posted by NHvette
Is it a flexible hose ? I've seen flex extensions that might get you in there.
Good luck.
I seem to recall pressures up near or over 100psi, but as noted
above ... relative differences are more telling.
Good luck.
I seem to recall pressures up near or over 100psi, but as noted
above ... relative differences are more telling.
Yeah, there's a rubber hose that'll screw right in, problem being you have about 18" of hose you're twirling around while screwing into the hole. It's a little easier using the extension adapter which screws into the plug hole first bringing the hole out further where you can see it.
Safety Car
Joined: Jul 2001
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From: York PA
Originally Posted by Jughead
Yeah, there's a rubber hose that'll screw right in, problem being you have about 18" of hose you're twirling around while screwing into the hole. It's a little easier using the extension adapter which screws into the plug hole first bringing the hole out further where you can see it.
Melting Slicks
Joined: Feb 2003
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St. Jude Donor '03,'11
put your thumb over the spark plug hole and have your wife crank the engine and be done with it. You are either going to have plenty of compression or your not.
you're keeping us in eternal suspense here.
you're keeping us in eternal suspense here.
