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| Rpm drop & head gasket Q https://www.ausmini.com/forums/viewtopic.php?f=2&t=48743 |
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| Author: | MUNKEY [ Sat Dec 27, 2008 11:01 pm ] |
| Post subject: | Rpm drop & head gasket Q |
When i pull each lead off the engine the first cyl makes a big difference and the rpm drops a fair bit but on number four when i pull the lead off it doesnt make much diference. why is this?, ive swaped plugs and leads between the two but its still the same outcome. How can i diaognose/what are the signs of a blown head gasket other than oil in the water & water in the oil? thanks 
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| Author: | 1310/71 [ Sat Dec 27, 2008 11:08 pm ] |
| Post subject: | |
Can't explain the rev drop but your other question about diagnosis. A compression check on each cylinder can in some circumstances help diagnose a headgasket issue (particularly if you had a benchmark previously which suggested they were similar to begin with). KB |
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| Author: | drmini in aust [ Sun Dec 28, 2008 5:57 am ] |
| Post subject: | |
1&4 should drop the same rpm, but if motor has a big cam in you will probably find 2&3 have less rpm drop than 1&4. Blame the siamesed inlet ports I think... 
If 1&4 are different it could be a leaky valve, or worn rings, in one cylinder. Not always a head gasket....
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| Author: | mugginsmoo [ Sun Dec 28, 2008 7:59 am ] |
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number 1 cylinder will always have a bigger effect than the rest. this is because the engine is timed to number 1, and the other cylinders "follow" along. every engine has a certain amount of tolerance (+ or -), this goes for the crank journal timing in relation to each other, they can be (and usually are) a few degrees out. rod lengths can vary, affecting compression ratios in each cylinder. even the cam lobes are not always perfect. unless you have "blue-printed" your engine there will be differences in how each cylinder works, its a compromise. |
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| Author: | DOZ [ Sun Dec 28, 2008 8:18 am ] |
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Go buy a compression gauge - they are cheap enough. I check my cylinder pressures at every oil change and write them down. Daniel |
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