| Author |
Message |
Mike Z (Spike308)
New member
Username: Spike308
Post Number: 38
Registered: 1-2003
| | Posted on Wednesday, July 23, 2003 - 9:02 am: | |
thanks....
very helpful |
Mitch Alsup (Mitch_alsup)
Member
Username: Mitch_alsup
Post Number: 898
Registered: 4-2002
| | Posted on Tuesday, July 22, 2003 - 1:47 pm: | |
If you get any useful leak-down in a leak-down (duh) test, you can then use you ear to listen for which part of the combustion chamber needs work: a) intake valves his back into the (duh) intake, b) exhaust valves leak into the (duh) headers, c) rings or upper cylinder wear leak into the oil pan. |
Andrew A. Illes (Andyilles)
Junior Member
Username: Andyilles
Post Number: 169
Registered: 10-2002
| | Posted on Tuesday, July 22, 2003 - 11:27 am: | |
Ooops... forgot to answer the "what does it mean" part. Both test cylinder sealing/integrity, i.e. are cylinders efficiently utilizing combustion pressures to generate power.. or leaking it out. Obviously, you want that pressure working on the pistons... not leaking out. |
Andrew A. Illes (Andyilles)
Junior Member
Username: Andyilles
Post Number: 168
Registered: 10-2002
| | Posted on Tuesday, July 22, 2003 - 11:20 am: | |
Hi Doc.. I'll try to answer. Both tests are performed with the engine warm, and all spark plugs removed.
Compression tests measure maximum pressure in psi that cylinders can achieve at starter speed. The tester (just a pressure guage) is screwed into each plug hole in turn, and the engine is cranked until the guage reaches max pressure. Readings are recorded. 140 to 160 psi is about right, but the key indicator is variance between cylinders.
A leakdown test requires an air compressor and a special 2 guage tester, which is screwed into a plug hole with that piston at TDC, and air is admitted at a constant 100 psi. The second guage reads the pressure the cylinder can maintain and reports in % terms... e.g. if the cylinder keeps at 98 psi, the guage will report 2% leakdown... if 88 psi, then 12% leakdown.
Though similar to compression testing, leakdown tests are more useful as a diagnostic. Listening to the crankcase, carb, and exhaust - or seeing air bubbles in the radiator overflow - pinpoints exact locations of ring, valve (and whether I or E,)or head gasket leakage.
Hope that helps.
Regards,
Andy |
Mike Z (Spike308)
New member
Username: Spike308
Post Number: 37
Registered: 1-2003
| | Posted on Monday, July 21, 2003 - 6:00 pm: | |
forgive my ignorance...
what does the compression test part of the PPI test / what does it mean?
How about the leakdown? |
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