Mike,
As already mentioned, I would expect the readings on a U20
to be a higher than 120 psi... but then again your compression
gauge maybe in error!
First... break loose the spark plugs when the engine is ice cold.
A little anti-sieze on the treads is a good idea.
Start the car and warm up to normal operating temp.
Pull the little wire off distributor. (that goes to the points).
Remove all four plugs.
PLACE A HEAVY BRICK OF THE THROTTLE! You want to keep the
throttle wide open during a compression test. Remove the little
fluid dampers ontop of the carb domes (allows the piston to reise
easier).
Start with #1 (towards the radiator). Have a friend crank the engine.
You should see study pulses rising on the compression.
Repeat with # 2-#4.
When you go to check #4... place oil into #1 cylinder (about 2cc,
less than half a teaspoon). Oil will coat #1 as you crank #4,
and displace the excess (yech, were old clothes). Repeat 1-4
with "wet compression check".
Hopefully you should see consistant readings. Post what you find
when WET and DRY.
I have gotten into the habit of RECHECKING #1 when I am all done.
I had a piece of carbon lodge in my nice MAC TOOLS compression
tester. Halfway though the dry test I got bad readings. Since
I usually check my own cars, I couldn't believe it as #3 & #4
were way down... meaning a blown headgasket. Thankfully I rechecked
#1... then puzzled, discovered the problem (reading was 140, and
dropped to 60 second time I checked it). Carbon removed... everything
was fine. Whew! Never forget the best tool is the one between
your errors.
Cheers,
Tom Walter
P.S. It took some years to LEARN all this. Like Daniel It took
a while to realize which cylinder was #1! I never did get the
firing order correct... just learned to leave the wires attached
to the distributor cap when I pulled the distributor out. WHen
installing a new cap, I'd just transfer one wire at a time.
Wasn't till years later I realize Subaru and VW labelled the
cylinders different. Hence they had did firing orders, yet
were identical. I like inlide fours! ;-)
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