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
Flatoo8@aol.com wrote:
>
> I recently was given a dual gauge leak down tester to replace my homemade
> single
> gauge unit. No instructions (can't complain, free is a good price). I am
> confused (old). How do I use this thing? I know about getting the cyl.s @ TDC
> but after that ...? To confound things, this is a two stroke engine. TIA,
> Chas.
/// unsubscribe/change address requests to majordomo@autox.team.net or try
/// http://www.team.net/mailman/listinfo
/// Archives at http://www.team.net/archive/vintage-race
|