Thanks Craig, very enlightening. I'll be trying it on my 250gp bike
first (which I believe is running as well as ever). It will be
interesting
indeed.
Don Tiana
Topanga Cyn., CA.
Still searching for that elusive Lotus Eleven
On Fri, 28 Jun 2002 08:31:10 -0700 Craig Wright
<cwright@pdghightower.com> writes:
> Hi Chas,
>
> Being a two stroke won't change how it is used, except you don't
> have to worry it you are
> at TDC on a comporession stroke or not. For you, TDC is always a
> comporession stroke.
>
> Leak down gauges have a very small orifice between the two gauges.
> One gauge reads
> incoming air pressure and the othe reads pressure in the cylinder.
> The difference between
> the two readings is the pressure loss accross the orifice as air
> flows through it. The
> leak down test is the industry standard and requirement for testing
> aircraft engines. It
> is an extremely sensitive test and will expose problems long before
> you would notice any
> reduction in performance.
>
> Typically use 80 psi to to the test.
> Make sure the engine is at TDC and out of gear.
> Screw the output hose into the spark plug hole. Make sure that it is
> snug and will not
> leak. Many units use an "O" ring on the adapter.
> Turn on the 80 PSI air and read the cylinder pressure.
> If the cylinder is perfect (very rare) both gauges will read the
> same, 80 PSI.
> Usually the rings leak some which will cause air flow through the
> orifice and reduce the
> reading on the cylinder pressure gauge.
> Since you don't have any valves all of your leakage will come from
> the rings. In a 4
> stroke the source of leakage is determined by listening in the
> exhaust pipe (exhaust
> valves), listening in the intake carburetor (Intake valves), or
> listening in the crankcase
> vent (Rings)
>
> Rules of thumb for 80 PSI input: (Only ring leakage is acceptable,
> any valve leakage will
> deteriorate quickly.)
> 70-80 - Excelent
> 60-70 - good/OK
> 45-60 - You won't notice any loss of power and it will still idle
> fine, but things are
> starting to wear. Start saving money for a rebuild
> <45 - Aircraft engines are grounded at this level, in a race car you
> may get several more
> races. You still will not notice any reduction in power.
>
> I have a 427 Ford that showed two cylinders at <15 PSI (the valve
> seats had stared to
> sink). The week end before, I was on the track and the engine was
> running great. As I said
> before, the test is extremely sensitive.
>
> Have fun,
>
> Craig Wright
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