Yep! I learned it from a Harley racer!
I agree with you all the way and the ring problem gets very interesting
with Dykes rings when you pressurize the cylinder slowly, sometimes you get
upwards of 75% leakage and when you pressurize it suddenly, the ring sets
and the leakage can go to near 0%.....
I try to do something about it if the leakage gets above 25% but have seen
the same cylinder go to 5% after the next pass!
Skip (Just adding more stuff to the confusion factor)
At 01:22 PM 6/4/01 , you wrote:
>Skip, that's very interesting, about the valves warping a little from
>standing open hot. Many years ago I recall some fellas I knew with hot
>Harley drag bikes had so much aggravation from the valves warping after
>a hard blast down the strip with their fuel bikes, they had a practice
>of jamming rags in the open pipes they used, as soon as they shut them
>off. They didn't remove the rags until it was time to run the bike
>again.
>
>Ardun Doug pointed out to me a while back that when leakdown testing,
>small movements of the crank to change the piston position of a given
>cylinder minutely, around the TDC where you are supposed to test it,
>make big differences in the leakdown rate. From nothing more than tiny
>shifts in the lie of the rings on the cylinder walls and in the piston.
>I've found the same thing. I believe that any running of a perfect
>valve is going to create a little bit of seepage, and the rings have to
>leak a little even if they are "Total Seal" type. Don't forget the
>leakdown test is a static test, and doesn't entirely prove how much air
>will be trapped in the chamber under running conditions. It takes
>"time" for leakage to occur and there isn't much of it. I'm told the
>FAA is pretty lenient about the leakdown rates that FAA-licensed
>mechanics can approve on piston engines at periodic inspection
>intervals. I think you have to combine leakdown testing with
>compression testing to get a feel for what's going on in your cylinders,
>but true, if you have 30+% or more leakdown, it's too much. It needs
>some work.
>
>Cheers Bill
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