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LEAK DOWN Vs. COMP. TEST

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Posted (edited)

Am I doing something wrong? First a I did a Comp Test , whiched failed around 45-50 PSI but the leak down passed with flying colors. Does a leak down test disqualify a compression test ?

 

Thanks

2005 DRZ400

 

Edited by Bigmacdirt

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the DRZ S and SM has an auto decompressor on the cam to allow easier starting this would cause a bad comp test

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Did you hold the throttle wide open during comp test? And was the engine warm?

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2 minutes ago, Atolduso said:

Did you hold the throttle wide open during comp test? And was the engine warm?

Thottle open and Choke on , Engine runs very poorly to pretty much doesn't run

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5 minutes ago, Bigmacdirt said:

Thottle open and Choke on , Engine runs very poorly to pretty much doesn't run

Interesting. No idea, besides your compression tester is just faulty/leaking pressure around the fitting etc. 

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Just now, Atolduso said:

Interesting. No idea, besides your compression tester is just faulty/leaking pressure around the fitting etc. 

No Problem , thanks for trying to help , I tried 2 different Gauges and hoses/adapters both same results , Think It has something to do with this decompressor , I slightly saw something in the repair manual about it ,

 

 

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Posted (edited)
6 hours ago, Bigmacdirt said:

No Problem , thanks for trying to help , I tried 2 different Gauges and hoses/adapters both same results , Think It has something to do with this decompressor , I slightly saw something in the repair manual about it ,

 

 

Did you use the same hose on both test ? You need to remove the valve for the leak down test , otherwise You’re not pushing air into the engine and your gage will show no leak , ask me how i know. 

Edited by habs
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All DRZ's have an auto release on the stock ex cam. With this decompression working the factory manual states compression should be around 130 psi.

Compression test is a good quick health check.

Leak down test goes further in helping you diagnose where you are loosing compression.

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11 hours ago, Bigmacdirt said:

Am I doing something wrong? First a I did a Comp Test , whiched failed around 45-50 PSI but the leak down passed with flying colors. Does a leak down test disqualify a compression test ?

 

Thanks

2005 DRZ400

 

With stock cams compression test results have  compared against specs accounting for the dcomp device.  Did you use jumper cables, jump pack or other power source while cranking the bike? Throttle full open?
After the low test numbers did you try again having squirted some oil in the cylinder?

You did not say what the leak down test numbers were that you felt passed with "flying colors"...assuming leakage was 15% or less or "passed with flying colors"

In answer to you question, NO ,if both tests were down correctly with functioning tools I can see no way to get 30-40psi on a compression test and 85% or better on a leak down test

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Posted (edited)
2 hours ago, Erik Marquez said:

With stock cams compression test results have  compared against specs accounting for the dcomp device.  Did you use jumper cables, jump pack or other power source while cranking the bike? Throttle full open?
After the low test numbers did you try again having squirted some oil in the cylinder?

You did not say what the leak down test numbers were that you felt passed with "flying colors"...assuming leakage was 15% or less or "passed with flying colors"

In answer to you question, NO ,if both tests were down correctly with functioning tools I can see no way to get 30-40psi on a compression test and 85% or better on a leak down test

No Jumper or Squirt of oil ( how much oil)

 

I am 110% sure that I am using the right hoses , valved for comp test and no valve for leak down

 

Using a OTC leak down gauge , set 90 psi going in , second gauge is pounds held in Chamber which reads 86 psi 

 

 

 

 

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Edited by Bigmacdirt

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Compression is a dynamic test (moving parts) and leak-down is static. If only a a portion of the cylinder wall was badly scored you may indeed have a low compression reading and if the piston/rings happened to be located on a "good" zone of the cylinder while running a leak-down it could result in a good test.

But as most others have said, check to make sure valves are fully closed first.

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