That was a good read - you just had to pull one for a Porsche though, didn't you?
On Apr 19, 2011, at 8:57 AM, Gene Henry wrote: > The real poop: Cylinder leak down testing: from > http://www.carcraft.com/techarticles/116_0406_cylinder_leakdown_tester/index1.html > > More poop: from > http://www.dietersmotorsports.com/Compression-leakdowntest.htm > Compression test vs. Cylinder leak down > How, why and what do they mean? > > When the time comes to purchase a used vehicle the first question that comes > to most prospective buyers minds is, “How’s the compression?” This has been > the standard engine condition test since the internal combustion engine was > invented. > > But what exactly is a compression test; and what do the readings tell us? > > A compression test measures how much pressure the piston creates in the > cylinder when traveling from bottom dead center (BDC) to top dead center > (TDC) with the valves closed. The reading is taken at the spark plug fitting > in the cylinder head. > > Because we are trying to recreate normal operating conditions there are a few > parameters that need to be met before performing the test. > > • The engine must be at or near operating temperature. > • All the spark plugs must be removed. (It is advisable to loosen all the > spark plugs ½ turn, and then start the engine for 15 seconds. Then completely > remove the spark plugs from the cylinder head. This blows out any carbon that > might get broken loose and caught between the valve and valve seat. If this > were to happen you could get a false, low compression reading.) > • The throttle must be all the way open (WOT) > • The ignition and/or fuel system should be disabled > > It is important to disable the ignition/fuel system for safety reasons and > engine health, as well as operator health. > > Most Porsches produced after 1983 have a single DME relay, which can be > removed to disable fuel and spark. On earlier 911s the 14-pin engine plug in > the left rear corner can be removed and then bridge connector 1 & 14 to crank > the engine. > > Insert the compression gauge into the proper spark plug hole and crank the > engine 5-6 times noting the first and final readings. Repeat on each > cylinder. More important than the exact number of times the engine is > cranked, is the consistency between cylinders. If you crank #1 cylinder 6 > times, all cylinders must be cranked 6 times. Another concern is the battery > condition. The engine must crank at the same speed for all cylinders. > > The most important factor in a compression test is consistency between > cylinders. A good rule of thumb is to have less than 10% variance between > cylinders. So if an engine has an average compression reading of 150-psi > there should be less than 15psi between the highest and lowest cylinders. > > Lets say for instance that we have the following compression readings: > 1-150, 2-180, 3-140, 4-145 > > 1,3 & 4 are all within the 10% specification but 2 is 20% higher than the > average of the other cylinders. Does this mean number three is high or the > others are low? > > To get to the bottom of this question we need to start by examining the spark > plugs. Do they all look the same? Is #2 badly carbon fouled? If you have one > or more cylinders with high compression and oil burning, the high compression > can be caused by the build-up of carbon on top of the piston. > > In our test case, the high compression of #2 cylinder can be caused by > excessive carbon build-up on the piston. Now to prove it! > > Cylinder leakdown test- > > While a compression test is a dynamic test (engine moving), a cylinder > leakdown test (C.L.T.) is a static test (engine at rest). The compression > test measures how much pressure the engine can produce while cranking; in > contrast to the C.L.T., which measures how much pressure is lost in the > engine. In a C.L.T. the engine is placed on TDC of the cylinder in question > and using a similar type of connector as the compression test, we fill the > cylinder with pressure. The tester then measures the volume of air needed to > maintain a predetermined pressure in the cylinder. This reading is expressed > in a percentage. Good cylinder leakdown readings should be below 5-8%. > > The great thing about C.L.T. is that it deals with how well the cylinder is > sealing and nothing else. The readings are not affected by carbon deposits, > cam timing, or even engine cranking speed. > > Another great feature of the C.L.T. is the fact that you can hear where the > air is leaking out of the cylinder. When a cylinder has high percentage of > leakage, first check the oil filler cap. Do you hear a hissing sound? If so, > you may have pressure leaking by the rings. Is there air escaping out the > exhaust? Is it escaping out the intake system? Then a burned valve may be the > problem. If two adjoining cylinders have similar low readings and you hear > leakage out the other cylinder, then a failed head gasket may be the problem. > > Being able to pinpoint the exact source of the compression loss will tell you > where the problem is; and not just that you have one. This knowledge will > greatly assist you in the next step… the repair. > > > > ----- Original Message ----- > > From: Kurt Nolte > To: [email protected] > Sent: Monday, April 18, 2011 11:47 PM > Subject: Re: [Nighthawk Lovers] Need some help - I think the GS-1000 has a > major issue > > How much pressure do you use for your leakdown tests? Just curious. > > Kurt > > >> On Apr 19, 2011 12:23 AM, "[email protected]" <[email protected]> >> wrote: >> >> and my buddy was just talking about his leak down testers today.... As a >> matter of fact there sitting on my nav station right now..... >> >> sorry, not constructive, just an observation >> >> paul >> -----Original Message----- >> Date: Monday, April 18, 2011 10:06:47 pm >> To: <nighthawk_lovers@googlegrou... >> >> From: "Gene Henry" <[email protected]> >> Subject: Re: [Nighthawk Lovers] Need some help - I think th... >> >> Cylinder Leak-Down Tester >> Item #94190 Only:$39.99 (less 25% Easter Sunday!) >> >> >> Hope this will help.... >> >> Hello All, >> Discovered today in the 140 odd miles since I did an oil >> change the GS-1000... >> > > > -- > You received this message because you are subscribed to the Google Groups > "Nighthawk Motorcycle Lovers!" group. > To post to this group, send email to [email protected]. > To unsubscribe from this group, send email to > [email protected]. > For more options, visit this group at > http://groups.google.com/group/nighthawk_lovers?hl=en. > > -- > You received this message because you are subscribed to the Google Groups > "Nighthawk Motorcycle Lovers!" group. > To post to this group, send email to [email protected]. > To unsubscribe from this group, send email to > [email protected]. > For more options, visit this group at > http://groups.google.com/group/nighthawk_lovers?hl=en. -- You received this message because you are subscribed to the Google Groups "Nighthawk Motorcycle Lovers!" group. To post to this group, send email to [email protected]. To unsubscribe from this group, send email to [email protected]. For more options, visit this group at http://groups.google.com/group/nighthawk_lovers?hl=en.
