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#2407879 - 11/23/17 12:09 PM Stock 1970 340 T/A Block Compression Test
f2502011 Offline
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Registered: 04/19/12
Posts: 274
Loc: US
I did a cold dry compression test on a stock 1970 340 T/A block. Engine hasn't been cranked in several weeks. Air cleaner in place, throttle plates closed. Ambient temp ~60 degrees. I still need to do a wet test and one after it’s warm and throttle plates open air cleaner off. Results were all consistent except one cylinder. Not sure what they are supposed to be. Any help with this that anyone offer would be greatly appreciated.

Right 78 80 83 85


Front-------------------->Rear


Left 82 80 85 110
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1970 EK2 T/A 727

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#2408033 - 11/23/17 07:01 PM Re: Stock 1970 340 T/A Block Compression Test [Re: f2502011]
Grizzly Online   tonguue
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Registered: 08/24/05
Posts: 4742
Loc: at work
I'd say you have one cylinder with good valves.

The rest doesn't look so good. twocents

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#2408051 - 11/23/17 07:56 PM Re: Stock 1970 340 T/A Block Compression Test [Re: f2502011]
fastmark Offline
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Registered: 01/20/03
Posts: 4413
Loc: Abilene, Texas
A leak down test is best to determine true condition of the motor.

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#2408071 - 11/23/17 09:01 PM Re: Stock 1970 340 T/A Block Compression Test [Re: Grizzly]
f2502011 Offline
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Registered: 04/19/12
Posts: 274
Loc: US
Originally Posted By Grizzly
I'd say you have one cylinder with good valves.

The rest doesn't look so good. twocents


Do you think it needs a head job or complete rebuild? Test was done in a way that would likely provide the lowest possible reading. Cold, throttle closed, dry, air cleaner on.
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1970 EK2 T/A 727

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#2408112 - 11/23/17 10:16 PM Re: Stock 1970 340 T/A Block Compression Test [Re: f2502011]
Grizzly Online   tonguue
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Registered: 08/24/05
Posts: 4742
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I'm not 100% sure, you should post in Unlawfuls Race and Engine tech section.

I'm used to seeing one really low cylinder if I've got a miss, but 7 down? Something must be really wrong there.......

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#2408119 - 11/23/17 10:46 PM Re: Stock 1970 340 T/A Block Compression Test [Re: f2502011]
fastnos Offline
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Registered: 11/30/06
Posts: 500
Loc: Jasper, Indiana
How did it run when you last started it up? Really need to do it right, throttle wired wide open, charged battery, then follow up with about 3 or so squirts of oil in each cylinder as you do a wet test. Not really enough info to give you even an educated guess.
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#2408210 - 11/24/17 10:04 AM Re: Stock 1970 340 T/A Block Compression Test [Re: fastnos]
f2502011 Offline
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Registered: 04/19/12
Posts: 274
Loc: US
Originally Posted By fastnos
How did it run when you last started it up? Really need to do it right, throttle wired wide open, charged battery, then follow up with about 3 or so squirts of oil in each cylinder as you do a wet test. Not really enough info to give you even an educated guess.


I think it runs pretty good but doesn’t really have the power it should. So I decided I would check compression. Should I warm it up first before checking again or is it okay to do it cold?
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#2408217 - 11/24/17 10:30 AM Re: Stock 1970 340 T/A Block Compression Test [Re: f2502011]
buildanother Offline
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Registered: 08/30/05
Posts: 10930
Loc: chicagoland,usa
I would run it up to operating temperature, then shut it down and wait maybe an hour or so, then test. You can roll it through about 4 cycles as the first and second are still pumping up the gauge hose etc. Those numbers you have do not sound right.(Too low)

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#2408325 - 11/24/17 02:17 PM Re: Stock 1970 340 T/A Block Compression Test [Re: buildanother]
dogdays Online   content
I Live Here

Registered: 01/20/03
Posts: 15912
Your test results don't mean anything. Your procedure was incorrect. Nobody seems to have noticed that.

The correct procedure for a compression test is remove all spark plugs, block throttle wide open, then do compression test. The engine has to spin over at least three times to get a good reading.

Sorry I'm sounding so cranky. My wife didn't even make me a turkey sandwich yesterday.

R.

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#2408380 - 11/24/17 04:59 PM Re: Stock 1970 340 T/A Block Compression Test [Re: f2502011]
f2502011 Offline
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Registered: 04/19/12
Posts: 274
Loc: US
With the throttle wide open will I need to do anything to the fuel supply? I’m going to test it tomorrow. Also if the results tomorrow are consistent with these what is the likelihood the valves are out of adjustment?


Edited by f2502011 (11/24/17 05:47 PM)
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1970 EK2 T/A 727

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#2408433 - 11/24/17 07:54 PM Re: Stock 1970 340 T/A Block Compression Test [Re: f2502011]
Pacnorthcuda Offline
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Registered: 11/19/07
Posts: 18722
Loc: Kirkland, Washington
Originally Posted By f2502011
With the throttle wide open will I need to do anything to the fuel supply? I’m going to test it tomorrow. Also if the results tomorrow are consistent with these what is the likelihood the valves are out of adjustment?


No on the fuel supply--it's fine. Just be sure when you open the butterflies you get them open on the first attempt so you don't dump a bunch of gas into the motor by operating the accerator pump more than the one time.

Pull your coil wire so there is no arcing from plug wires laying around--that's a fire hazard if the motor spits any fuel out the plug holes.

Charge your battery! You want a fully charged batt.

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#2408492 - 11/24/17 09:56 PM Re: Stock 1970 340 T/A Block Compression Test [Re: f2502011]
NANKET Offline
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Registered: 12/13/03
Posts: 3766
Loc: northwest USA
Don't pull the coil wire because the cool will still make a spark.

Remove the wire from the ballast resistor, the side where the blue and brown wires that go into one connector at the resistor.

Remove the throttle return spring and the carb stays open a lot easier.

Do this with the engine warm-hot, don't let it cool for an hour.

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#2408511 - 11/24/17 10:41 PM Re: Stock 1970 340 T/A Block Compression Test [Re: NANKET]
Pacnorthcuda Offline
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Registered: 11/19/07
Posts: 18722
Loc: Kirkland, Washington
Originally Posted By NANKET
Don't pull the coil wire because the cool will still make a spark.

Remove the wire from the ballast resistor, the side where the blue and brown wires that go into one connector at the resistor.

Remove the throttle return spring and the carb stays open a lot easier.

Do this with the engine warm-hot, don't let it cool for an hour.


Ya pull the coil wire out of the coil--no spark. Pulling the ballast wires will work too.

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#2408514 - 11/24/17 10:52 PM Re: Stock 1970 340 T/A Block Compression Test [Re: Pacnorthcuda]
amxautox Offline
Still Retired. Still Posting on Moparts. A Lot.

Registered: 05/13/03
Posts: 96083
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warm engine

wire throttle FULLY open, that'll shut off any fuel supply as the fuel won't flow unless there is air passing thru the carb, which it won't be at cranking speed, which is also how you start a flooded engine.

by the time you remove all the plugs, the engine will be cool enough

spin the motor over a FEW times, that'll spit out any fuel in the system -intake, carb passageways, head passageways, combustion chamber.

screw in the gauge and go for it.

crank a minimum of 3 revolutions

don't worry about any spark, as there won't be any fuel there, just don't touch any wires while doing the test, as in holding the gauge too close to a wire. laugh2 If you really want to, then just pull the coil wire from the coil.

Oh, and there won't even be any sparks if you don't use the ignition key to crank over the engine, that is what a remote starter switch is for. Buy one, or make one using a push button momentary switch from the hardware store, been there, done both, have both.


Edited by amxautox (11/24/17 10:57 PM)
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#2408549 - 11/25/17 12:27 AM Re: Stock 1970 340 T/A Block Compression Test [Re: NANKET]
f2502011 Offline
enthusiast

Registered: 04/19/12
Posts: 274
Loc: US
Originally Posted By NANKET
Don't pull the coil wire because the cool will still make a spark.

Remove the wire from the ballast resistor, the side where the blue and brown wires that go into one connector at the resistor.

Remove the throttle return spring and the carb stays open a lot easier.

Do this with the engine warm-hot, don't let it cool for an hour.


How's the best way to do a hot test without burning myself or melting a plug wire or compression gauge hose or ??? on a manifold?
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1970 EK2 T/A 727

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#2408555 - 11/25/17 12:58 AM Re: Stock 1970 340 T/A Block Compression Test [Re: f2502011]
Pacnorthcuda Offline
I Live Here

Registered: 11/19/07
Posts: 18722
Loc: Kirkland, Washington
Originally Posted By f2502011
Originally Posted By NANKET
Don't pull the coil wire because the cool will still make a spark.

Remove the wire from the ballast resistor, the side where the blue and brown wires that go into one connector at the resistor.

Remove the throttle return spring and the carb stays open a lot easier.

Do this with the engine warm-hot, don't let it cool for an hour.


How's the best way to do a hot test without burning myself or melting a plug wire or compression gauge hose or ??? on a manifold?


Just do the best you can. On my 440 Cuda access to the plugs is a beech. If the engine/headers are hot it's brutal.
There are other cars that you can perform the test on a much warmer engine.
The main thing is you want SOME warmth in the engine. It also ensures the oil rings are well lubed from the recent run, thereby ensuring some oil sealing of the piston/cylinder.

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#2408584 - 11/25/17 06:44 AM Re: Stock 1970 340 T/A Block Compression Test [Re: f2502011]
fastmark Offline
master

Registered: 01/20/03
Posts: 4413
Loc: Abilene, Texas
You are working on a small block here. A spark plug socket and a long extension are your friend. No manifolds to touch that way.

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#2408668 - 11/25/17 11:26 AM Re: Stock 1970 340 T/A Block Compression Test [Re: fastmark]
Cab_Burge Offline
Too Many Posts

Registered: 08/23/03
Posts: 29942
Loc: Bend,OR USA
As already said use a battery charger when testing and repeat the first test with the throttle opened and then warm the motor up (get it HOT, not barely warm tsk ) and do it again, you may be pleasantly surprised with the differences luck
What do you know about this motor? Was it rebuilt or is it is a stock motor with a lot of miles on it?
BTW,#7 is the leanest cylinder usually on most V8 with that have the firing order when #5 cylinder fires 90 degree before #7, especially on single plane single four barrel intake manifolds, not so much on stock Mopar intakes work scope
Let us know your results thumbs


Edited by Cab_Burge (11/25/17 11:27 AM)
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#2408676 - 11/25/17 11:55 AM Re: Stock 1970 340 T/A Block Compression Test [Re: fastmark]
Sixpak Offline
master

Registered: 01/20/03
Posts: 6132
Loc: The Swamp
Originally Posted By fastmark
You are working on a small block here. A spark plug socket and a long extension are your friend. No manifolds to touch that way.


And a piece of rubber fuel line can be pushed over the spark plug ends, once they are loose, to remove them and not burn yourself. Also works great to reinstall the plugs and not cross thread them.

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#2408681 - 11/25/17 12:14 PM Re: Stock 1970 340 T/A Block Compression Test [Re: Sixpak]
amxautox Offline
Still Retired. Still Posting on Moparts. A Lot.

Registered: 05/13/03
Posts: 96083
Loc: On The Boat, On The Lake, Wa. ...
Originally Posted By Sixpak
Originally Posted By fastmark
You are working on a small block here. A spark plug socket and a long extension are your friend. No manifolds to touch that way.


And a piece of rubber fuel line can be pushed over the spark plug ends, once they are loose, to remove them and not burn yourself. Also works great to reinstall the plugs and not cross thread them.
Yup, on the hose. A spark plug socket is best, it already has the rubber insert to hold the plug. grin
_________________________
Tom

"Everyone should believe in something; I believe I'll go fishing."

-Henry David Thoreau

Men and fish are alike. They both get into trouble when they open their mouths

author unknown


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