Thread: leak down results

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these are the results of a leak down test done recently on a 1969 427/400 3963512 block

1 3 5 7
35% 18% 16% 23%


2 4 6 8
18% 43% 33% 30%

What's it look like the problem may be? The engine was running great before the test was done. Good oil pressure, ran fairly cool, started up easily, but noticed a little smoke from the R exhaust on startup, that disappeared after 30 seconds.

Was the spark plug #4 a little oily????

One common thing on BBC and especially older ones are that the valve seals fall apart and oil the cylinders---

Idea of doing leakdown tests is that you can listen at intake, exhaust, valve cover breather to see where IT SOUNDS LIKE THERES A LEAK!!!!

Hello Jerry,

I didn't do the test, but was told it was probably the rings. I guess what you are saying is that you can't tell from the pattern?

No--the pattern there would be about the same as doing a compression check----a leakdown lets you listen for the air escaping which will tell if its rings, intake, exhaust valve, gasket, etc