Greetings Jim,
The following is taken from our Technical page of the Cape Cod
British Car Club's website. This has been assembled by Jay Welch, our
club secretary. Lot's of the info is culled from postings on this list
and others, and offers valuable assistance to other enthusiasts. (and
thanks for the kind words...)
Good luck with the smokin' blues,
Kevin Thompson
Cape Cod British Car Club
http://clubs.hemmings.com/capecodbritish
Leakdown Test - 1. Take out all spark plugs. 2. Bring cylinder #1 to
TDC (top dead center) on the compression stroke. At this point, all
valves for that cylinder will be closed. An easy way to determine TDC
is to turn the crank in its normal direction with your thumb plugging
the spark plug hole until you can feel compression building. Then place
a long, thin, dowel with a rounded end in the spark plug hole to find
the point at which the dowel is neither rising nor going down. I like
to use a rounded end to avoid the dowel digging into the piston if it
gets jammed. 3. Remove the dowel, screw the gauge adapter into the
spark plug hole & connect the gauge. The gauge has a fitting to connect
the extender hose to the spark plug hole, & another to connect the air
hose. 4. Apply the compressed air (about 80 lbs) & modulate the knob to
get a steady reading from both faces on the gauge. Use the same pressure
on all cylinders. You may need an assistant to either hold the
crankshaft still or step on the brake while in gear. 5. LISTEN for the
sound of compressed air. Remove the oil filler cap & listen. If you can
clearly hear a whooshing/howling sound you're losing compression through
the rings. Listen at the exhaust pipe. If you can hear it or even feel
puffs on your hand it is your exhaust valves. Listen at the throttle
body & intake manifold. If you can clearly hear a whooshing/howling It
is your intake valves. If the results are inconclusive, it is probably
your head gasket. If you suspect a blown head gasket, which has
symptoms such as reduced power, white or blue smoke out the tailpipe,
oil in the coolant or coolant in the oil, listen at an adjacent plug
hole. If you can hear the air you have a bad head gasket. Remove the
coolant cap & watch the coolant level when you add the compressed air.
If it rises or you see bubbles, you have a leaking head gasket.
Hydrocarbons detected in the coolant is another symptom. 6. Continue to
cylinders 5, 3, 6, 2 & 4. Much like the compression test, when you are
looking at gauge readings you should be looking for consistency.
Consistently low numbers across all cylinders is most likely just
showing varying degrees of normal wear. You will be judging engine wear
by reading the percentage of leakdown indicated by the leakdown gauge.
Leakdown gauges start around $70. For more technical information on the
leak down test, see http://www.w-p-c.com/buggyleakdown.htm &
http://www.vclassics.com/archive/leakdown.htm You can also use a more
primitive form of this test by pumping air into the cylinder without the
leakdown gauge. Performing the test this way might give you a feel for
where the problem lies. You can make your own single gauge leakdown
tester by visiting http://www.briggs-racing.com/tech/leakd.htm or
http://members.tripod.com/~Wrenchbender/leakdown.html
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