Compression Test results - We have a problem
Thread Starter
Le Mans Master
Joined: Sep 2000
Posts: 9,078
Likes: 7
From: DFW TX
Cruise-In VII Veteran
St. Jude Donor '07
Compression Test results - We have a problem
Started working on the car again tonight with a friend and I need help with my results.
1 - 135
2 - 160
3 - 170
4 - 150
5 - 180
6 - 165
7 - 170
8 - 130
Looks like 1 and 8 have some type of problem. We plugged a pressurized hose to 1 and it would pressure up, then bleed of a few psi, then pressure up again. Process just repeats itself. Some of the other cylinders just slowly bleed off pressure. What's going on with it? :confused:
1 - 135
2 - 160
3 - 170
4 - 150
5 - 180
6 - 165
7 - 170
8 - 130
Looks like 1 and 8 have some type of problem. We plugged a pressurized hose to 1 and it would pressure up, then bleed of a few psi, then pressure up again. Process just repeats itself. Some of the other cylinders just slowly bleed off pressure. What's going on with it? :confused:
Le Mans Master
Joined: Aug 2000
Posts: 9,662
Likes: 7
From: Semper ubi, sub ubi
Cruise-In VI Veteran
Cruise-In VII Veteran
Re: Compression Test results - We have a problem (Budman78)
Buddy the only way I know of the really narrow down the cause of the leak down is to do a real leak down test, with the right setup. I've seen it done a few times by mechanics, and I know it requires some specialized gauges and equipment. Done right it should tell you if it is a the valves or rings.
But, looking at your readings I'd take a wild guess that you have some burnt exhaust valves on #1 and #8.
But, looking at your readings I'd take a wild guess that you have some burnt exhaust valves on #1 and #8.
Race Director
Joined: Apr 2000
Posts: 17,676
Likes: 201
From: Who says "Nothing is impossible" ? I've been doing nothing for years.
Re: Compression Test results - We have a problem (Smokehouse69)
Turn it over about eight times and the pressure you see on the dial is what you go by. All cylinders will slowly bleed off pressure after you stop the test. Some of the cylinders are OK (around 180psi) others are in trouble, Sould not have more thatn 10% difference between top and low cylinders.
You can do a poor man's leak down test if you have compressed are just pumo it into the cylinders and listen where you hear it leaking out, thru the diptick or tailpipe it is the rings and thru the carb it is the valves. Note that you will still hear a little hissing even on good cylinders. :D
You can do a poor man's leak down test if you have compressed are just pumo it into the cylinders and listen where you hear it leaking out, thru the diptick or tailpipe it is the rings and thru the carb it is the valves. Note that you will still hear a little hissing even on good cylinders. :D
Safety Car
Joined: Jul 2002
Posts: 3,770
Likes: 3
From: St Louis MO
Re: Compression Test results - We have a problem (Budman78)
Jegs has a leakdown tester for less than $120.
http://www.jegs.com/cgi-bin/ncommerc...76&prmenbr=361
Brett :thumbs:
http://www.jegs.com/cgi-bin/ncommerc...76&prmenbr=361
Brett :thumbs:
Melting Slicks
Joined: Jun 2002
Posts: 2,843
Likes: 99
From: Orrtanna Pa.
Re: Compression Test results - We have a problem (Brettmc)
Put a shot of oil in the low cylinders through the spark plug hole,retest the compression. If it improves most likely the rings are shot.If not valves or cam lobe.You can do a visual on the cam by watching the rockers while you crank it over.
Racer
Joined: Jul 2003
Posts: 287
Likes: 0
From: Dayton Area Ohio
Re: Compression Test results - We have a problem (The Money Pit)
Quote: {Put a shot of oil in the low cylinders through the spark plug hole,retest the compression. If it improves most likely the rings are shot}
:iagree:
Also, re-adjust the rockers, and do another test just to be sure you have a good base to go by.
:iagree:
Also, re-adjust the rockers, and do another test just to be sure you have a good base to go by.
Thread Starter
Le Mans Master
Joined: Sep 2000
Posts: 9,078
Likes: 7
From: DFW TX
Cruise-In VII Veteran
St. Jude Donor '07
Re: Compression Test results - We have a problem (The Money Pit)
Food for thought...
Cam is functioning correctly.
#3 and #5 pressurize fine with a slight leak down. (Normal)
Why would #1 pressurize for a second or two, then make a pisssss noise. Then pressurize again. It seem if it was a burnt exhaust valve, it would just bleed off without holding pressure.
:confused:
Cam is functioning correctly.
#3 and #5 pressurize fine with a slight leak down. (Normal)
Why would #1 pressurize for a second or two, then make a pisssss noise. Then pressurize again. It seem if it was a burnt exhaust valve, it would just bleed off without holding pressure.
:confused:
Race Director
Joined: Sep 1999
Posts: 11,360
Likes: 382
From: Plano TX
Re: Compression Test results - We have a problem (Budman78)
Something in your write-up makes me wonder if you are testing this correctly...
1. Take all plugs out
2. Make sure battery is in good shape.
3. Connect compression gauge to #1
4. Block throttle fully open
5. Crank engine until needle stop climbing or max 10 revolutions.
1. Take all plugs out
2. Make sure battery is in good shape.
3. Connect compression gauge to #1
4. Block throttle fully open
5. Crank engine until needle stop climbing or max 10 revolutions.
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Thread Starter
Le Mans Master
Joined: Sep 2000
Posts: 9,078
Likes: 7
From: DFW TX
Cruise-In VII Veteran
St. Jude Donor '07
Re: Compression Test results - We have a problem (zwede)
Zwede, The only thing I didn't do is leave the throttle wide open. I will re-check tonight.
Le Mans Master
Joined: Apr 2000
Posts: 5,202
Likes: 10
From: cincinnati ohio
St. Jude Donor '09
Re: Compression Test results - We have a problem (Budman78)
Leak down test is the way to go, pressurize and then just listen to where the air is going...exhaust or carb=valve crankcase=rings or piston....
Thread Starter
Le Mans Master
Joined: Sep 2000
Posts: 9,078
Likes: 7
From: DFW TX
Cruise-In VII Veteran
St. Jude Donor '07
Re: Compression Test results - We have a problem (yellow 72)
Not good new... It seem she is broke. I filled #1 up with some oil and pressure tested it again. The gauge goes up to 170 and blows by. The best reading with oil was 150 average. Reassembled the plugs and started it up. It is pulsing bad at 3000 rpms. I either fried the crank or the convertor. :eek: :sad: :sad: :sad: :sad: :sad: :sad: :sad:
