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#2409358 - 11/26/17 08:09 PM Re: Stock 1970 340 T/A Block Compression Test [Re: f2502011]
f2502011 Offline
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Registered: 04/19/12
Posts: 280
Loc: US
I’m ready to do a leak down test. I have the harmonic balancer timing mark lined up at 0 and can see that the #1 piston is as close as it could be to the bottom of the spark plug or underside of the head. Couple of questions. The instructions say to do on a warm engine. Everything else I’ve read and heard say cold engine. Firing order I believe is 1-8-4-3-6-5-7-2. How much do I rotate the crank to get TDC on the next cylinder to test?
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1970 EK2 T/A 727

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#2409369 - 11/26/17 08:34 PM Re: Stock 1970 340 T/A Block Compression Test [Re: f2502011]
amxautox Offline
Still Retired. Still Posting on Moparts. A Lot.

Registered: 05/13/03
Posts: 96644
Loc: On The Boat, On The Lake, Wa. ...
90 degrees.
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"Everyone should believe in something; I believe I'll go fishing."

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

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#2409949 - 11/27/17 10:48 PM Re: Stock 1970 340 T/A Block Compression Test [Re: amxautox]
f2502011 Offline
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Posts: 280
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Originally Posted By amxautox
90 degrees.
I'm going to do the leak down on Weds. Just to make sure. I have the harmonic balancer at the 0 mark and it appears that #1 is TDC. I rotate the crank clockwise 90 degrees and cylinder 8 will be TDC another 90 degrees and 4 will be TDC and so forth and so on?
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#2409967 - 11/27/17 11:21 PM Re: Stock 1970 340 T/A Block Compression Test [Re: f2502011]
buildanother Offline
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Registered: 08/30/05
Posts: 11220
Loc: chicagoland,usa
as long as you're certain that it is set to fire #1 with timing mark lined up at top dead center, and not set to fire cyl #6 which also lines up the same way.

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#2409975 - 11/27/17 11:43 PM Re: Stock 1970 340 T/A Block Compression Test [Re: buildanother]
Cab_Burge Offline
I Win

Registered: 08/23/03
Posts: 31224
Loc: Bend,OR USA
Originally Posted By buildanother
as long as you're certain that it is set to fire #1 with timing mark lined up at top dead center and not set to fire cyl # 6 which also lines up the same way.

If you align the timing tab on zero with the timing mark on the balancer align with the tab on #1 it will not leak out of the valves very much, if it is align on #6 it won't hold any pressure at all due to it having both valves opened on #1 overlap stroke with #6 on the firing stroke shruggy work
Either way if it isn't on #1 TDC on the firing stroke you can move the hose to the other cylinder at TDC on the firing stroke (#6) and start testing from there work up


Edited by Cab_Burge (11/27/17 11:45 PM)
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#2410524 - 11/28/17 11:29 PM Re: Stock 1970 340 T/A Block Compression Test [Re: f2502011]
f2502011 Offline
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Registered: 04/19/12
Posts: 280
Loc: US
Not sure of the circumference of the harmonic balancer and I don't have timing tape. I believe when I have done something like this in the past I was able to use a piece of painters tape cut to an exact length and put marks at 90 degrees intervals around the balancer. I need to know the circumference of the balancer or the correct length of the piece of tape that I need to make to do a template that will allow me to make marks all around the balancer at 90 degree intervals so I can do the test correctly and efficiently.
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#2410762 - 11/29/17 01:31 PM Re: Stock 1970 340 T/A Block Compression Test [Re: Cab_Burge]
f2502011 Offline
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Registered: 04/19/12
Posts: 280
Loc: US
Originally Posted By Cab_Burge
Originally Posted By buildanother
as long as you're certain that it is set to fire #1 with timing mark lined up at top dead center and not set to fire cyl # 6 which also lines up the same way.

If you align the timing tab on zero with the timing mark on the balancer align with the tab on #1 it will not leak out of the valves very much, if it is align on #6 it won't hold any pressure at all due to it having both valves opened on #1 overlap stroke with #6 on the firing stroke shruggy work
Either way if it isn't on #1 TDC on the firing stroke you can move the hose to the other cylinder at TDC on the firing stroke (#6) and start testing from there work up


I just tried to do the test and I must be doing something wrong. I have #1 at TDC. Checked with a tool and harmonic balancer is lined up with zero. I tested #1 first and have 45% leakage. I hear a hissing in the opposite valve cover on the passenger side and can feel air coming out of the breather hole. So I moved over to #6 and same result 45% hiss and air on the same side. Thoughts?
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#2410764 - 11/29/17 01:35 PM Re: Stock 1970 340 T/A Block Compression Test [Re: f2502011]
amxautox Offline
Still Retired. Still Posting on Moparts. A Lot.

Registered: 05/13/03
Posts: 96644
Loc: On The Boat, On The Lake, Wa. ...
Air coming out of the valve cover breather would be air coming up from the oil pan, which would be coming past the piston, and therefore would be bad rings.

Turn the crank over a couple times and try again.

And make sure the rotor in the dist, is pointing to #1 tower. I also like to put my finger in #1 hole while cranking it up to #1 tdc to be sure it's the compression stroke. You can tell by the 'lots more' pressure building up, the exhaust stoke won't build up that much pressure. When close I'll watch the timing marks and piston top to be sure it's at tdc. That's where the straw comes in, sometimes you can, sometimes you can't see the piston top thru the sparkplug hole. Or use a bore scope. Just don't insert it very far so it doesn't get stuck between the piston and head. Barely stick it in the plug hole.
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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

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#2410786 - 11/29/17 02:06 PM Re: Stock 1970 340 T/A Block Compression Test [Re: amxautox]
f2502011 Offline
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Registered: 04/19/12
Posts: 280
Loc: US
Originally Posted By amxautox
Air coming out of the valve cover breather would be air coming up from the oil pan, which would be coming past the piston, and therefore would be bad rings.

Turn the crank over a couple times and try again.

And make sure the rotor in the dist, is pointing to #1 tower. I also like to put my finger in #1 hole while cranking it up to #1 tdc to be sure it's the compression stroke. You can tell by the 'lots more' pressure building up, the exhaust stoke won't build up that much pressure. When close I'll watch the timing marks and piston top to be sure it's at tdc. That's where the straw comes in, sometimes you can, sometimes you can't see the piston top thru the sparkplug hole. Or use a bore scope. Just don't insert it very far so it doesn't get stuck between the piston and head. Barely stick it in the plug hole.


I’m doing this on a cold engine and using low pressure (gauge says 7-100 psi) I’m using about 15-20 psi is this ok? Also if the rotor is pointing close to cylinder one on distributor does that mean it’s at TDC on compression stroke?
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#2410793 - 11/29/17 02:14 PM Re: Stock 1970 340 T/A Block Compression Test [Re: f2502011]
amxautox Offline
Still Retired. Still Posting on Moparts. A Lot.

Registered: 05/13/03
Posts: 96644
Loc: On The Boat, On The Lake, Wa. ...
Originally Posted By f2502011
Originally Posted By amxautox
Air coming out of the valve cover breather would be air coming up from the oil pan, which would be coming past the piston, and therefore would be bad rings.

Turn the crank over a couple times and try again.

And make sure the rotor in the dist, is pointing to #1 tower. I also like to put my finger in #1 hole while cranking it up to #1 tdc to be sure it's the compression stroke. You can tell by the 'lots more' pressure building up, the exhaust stoke won't build up that much pressure. When close I'll watch the timing marks and piston top to be sure it's at tdc. That's where the straw comes in, sometimes you can, sometimes you can't see the piston top thru the sparkplug hole. Or use a bore scope. Just don't insert it very far so it doesn't get stuck between the piston and head. Barely stick it in the plug hole.


I’m doing this on a cold engine and using low pressure (gauge says 7-100 psi) I’m using about 15-20 psi is this ok? Also if the rotor is pointing close to cylinder one on distributor does that mean it’s at TDC on compression stroke?
Yup.
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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

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#2410803 - 11/29/17 02:25 PM Re: Stock 1970 340 T/A Block Compression Test [Re: f2502011]
f2502011 Offline
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Registered: 04/19/12
Posts: 280
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Just checked distributor rotor and it’s pointing straight toward the back of the car so basically toward cylinder 6
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1970 EK2 T/A 727

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#2410816 - 11/29/17 02:40 PM Re: Stock 1970 340 T/A Block Compression Test [Re: f2502011]
amxautox Offline
Still Retired. Still Posting on Moparts. A Lot.

Registered: 05/13/03
Posts: 96644
Loc: On The Boat, On The Lake, Wa. ...
Turn the crank until the rotor points at #1 tower. Should be just one revolution of the crank.
_________________________
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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#2410977 - 11/29/17 07:13 PM Re: Stock 1970 340 T/A Block Compression Test [Re: f2502011]
f2502011 Offline
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Registered: 04/19/12
Posts: 280
Loc: US
Leak Down Results


Right 45% 45% 40% 50%


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


Left 45% 47% 45% 34%

Disclaimer: The gauge was new, but I don't trust the gauge at all. It would give consistently inconsistent results and was hard to get regulated. Sometimes it would go straight to 100% loss then you would have to reset it and start over because once it hit 100% it somehow cuts off the air flow. Never could get it to start at exactly 0 so some of the results with this gauge could be off by 5-10% or more. Turning the regulator on the gauge would some times get it in the yellow start range, right in the middle, but once I finished it would be out of that range. Also turning the regulator was so inconsistent in what it did on the gauge. Sometimes a lot of turning resulted in little movement of the needle and other times a little would make it move a lot or it would keep moving after it was set. I believe if the engine was warm it would have been much better but not for sure. Either way regardless I could hear air in each valve cover, out the breather port and dipstick hole. Nothing in the coolant and nothing at the exhaust. One time I got 100% loss over and over again and I ended up moving to the next cylinder I had previously tested and gotten different results and it did the same 100% loss vs 40% I got before. I got it regulated on that one cylinder and then went back to the other and ended up getting 47% instead of 100%. Thing is to go back to that cylinder I rotated the crank backwards 90 degrees. Is this okay? That's the only time I went backwards.
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#2411004 - 11/29/17 07:51 PM Re: Stock 1970 340 T/A Block Compression Test [Re: f2502011]
Cab_Burge Offline
I Win

Registered: 08/23/03
Posts: 31224
Loc: Bend,OR USA
You need to read what pressures that gauge instruction sheet wants you to use, I haven't seen any leak down gauge that will work below 50 lbs of pressure, but there are a lot of things in this world I haven't seen yet also shruggy
A single gauge unit probably wants between 80 and 100 lbs., my two gauge aircraft legal calls for 80 lbs static before starting and the using the regulator to bring the first gauge (left hand side looking down at them) back to 80 lbs. with the valve opened reading the leakage so I would see 80 Lbs. on the left gauge and say between 78 Lbs. to 0 lbs. on the right gauge with a hole in the piston or a broken valve shruggy
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#2411010 - 11/29/17 08:08 PM Re: Stock 1970 340 T/A Block Compression Test [Re: Cab_Burge]
f2502011 Offline
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Registered: 04/19/12
Posts: 280
Loc: US
Originally Posted By Cab_Burge
You need to read what pressures that gauge instruction sheet wants you to use, I haven't seen any leak down gauge that will work below 50 lbs of pressure, but there are a lot of things in this world I haven't seen yet also shruggy
A single gauge unit probably wants between 80 and 100 lbs., my two gauge aircraft legal calls for 80 lbs static before starting and the using the regulator to bring the first gauge (left hand side looking down at them) back to 80 lbs. with the valve opened reading the leakage so I would see 80 Lbs. on the left gauge and say between 78 Lbs. to 0 lbs. on the right gauge with a hole in the piston or a broken valve shruggy


It's a dual gauge setup. The instructions literally say "NOTE: Set the air compressor's regulator to 7 to 100 PSI. Never opperate this tester with air pressure set higher than 100 PSI which can damage this tool."
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1970 EK2 T/A 727

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#2411135 - 11/30/17 12:41 AM Re: Stock 1970 340 T/A Block Compression Test [Re: f2502011]
Cab_Burge Offline
I Win

Registered: 08/23/03
Posts: 31224
Loc: Bend,OR USA
Try testing it warm with the primary gauge pressure set at 80 and then divide your reading into each other, if it reads 78 on the low side and you divide 80 into that it equals 2.5%, correct scope
If you set the pressure at 100 Lbs. even and then read the low side it will read the percent leakage with no math, 100/98=2.0 %
Street motors that test from 3 % to 25 % aren't bad scope
If it leaks worst than 25 % then you have to decide to fix it or drive it until you can't stand the oil consumption and poor performance shruggy


Edited by Cab_Burge (11/30/17 12:42 AM)
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#2411167 - 11/30/17 07:01 AM Re: Stock 1970 340 T/A Block Compression Test [Re: f2502011]
fastmark Offline
master

Registered: 01/20/03
Posts: 4632
Loc: Abilene, Texas
I have never cut corners on tools. Mine is a two gauge Matco unit. Works real simple. Find tdc, input 100 lbs of air into the cly by first gauge, then read second gauge of the amount lbs it is maintaining. If it holds 80lbs, you have 20% leakage. Sounds like you have a worn out motor with bad rings to me.

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#2411258 - 11/30/17 10:35 AM Re: Stock 1970 340 T/A Block Compression Test [Re: Cab_Burge]
f2502011 Offline
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Registered: 04/19/12
Posts: 280
Loc: US
Originally Posted By Cab_Burge
Try testing it warm with the primary gauge pressure set at 80 and then divide your reading into each other, if it reads 78 on the low side and you divide 80 into that it equals 2.5%, correct scope
If you set the pressure at 100 Lbs. even and then read the low side it will read the percent leakage with no math, 100/98=2.0 %
Street motors that test from 3 % to 25 % aren't bad scope
If it leaks worst than 25 % then you have to decide to fix it or drive it until you can't stand the oil consumption and poor performance shruggy


I’ll retry this way some time next week. The thing is there’s no smoke or oil consumption. The gauge I’m using is from Harbor Freight. I don’t do a lot of these tests so I didn’t want to spend a small fortune on a gauge I may use once.
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#2411920 - 12/01/17 04:51 PM Re: Stock 1970 340 T/A Block Compression Test [Re: f2502011]
dogdays Offline
I Live Here

Registered: 01/20/03
Posts: 16216
Wow, next they'll be telling you to get a borescope!

Those compression numbers from your first legitimate test are low. They are lower than low.

You said there is a lot of carbon in the engine. Last year Hot Rod magazine in one of their "we fix a problem car" articles worked on a mustang and it had low compression in some holes. The mechanic said lets take it out and "blow the carbon out." I always thought that was just a myth. He told the writer that sometimes engines get carbon deposits holding the valve a little open and losing compression.
Go out and get the car warmed up[, do a bunch of hard acceleration runs and some high speed runs. That may help. Get back home and aim the exhaust system away from buildings, people, etc. Remove air filter and with engine running about 2500rpm, trickle some water into one side of the carb. You should get a blast of white steam, maybe carrying with it little chunks of carbon. It's pretty dramatic and will stain a wall or fence. Repeat for the other side. Take it out and run it back up to operating temp and do it again. This may help.

It sure sounds to me like rings aren't working. Try to seat the rings with some sharp acceleration blasts followed by letting the engine pull the car down to speed with throttle closed.

Leakdown tests can tell you the condition of things. If you pressurize a cylinder and air leaks out past the piston the next step is surgery.

R.

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#2411984 - 12/01/17 06:51 PM Re: Stock 1970 340 T/A Block Compression Test [Re: dogdays]
RapidRobert Offline
Circle Track

Registered: 11/20/03
Posts: 34008
Loc: Lincoln Nebraska
After "blowing the carbon out" likely you will need to clean/replace the plugs. On reseating the rings if you do rering here is a good read on ring sealing: go to www.mototuneusa.com & scroll down to & click on "breakin secrets". its a motorcycle oriented site but the principle works. their main take is (1) to run it HARD (with their procedure) for ring breakin (2) & you get ONE shot to get an excellent breakin that gives good leakdown numbers (as opposed to a so so breakin with average numbers).
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