[tech]: help with compression readings...pretty please?

[rabbit16v@prodigy.net (Dave Ewing)]

I would be concerned about the 170 because the 215's are more than likely
correct.  I get those readings regularly from 16v motors.  I would hope for
carbon buildup on the valve face/seat especially if it has been sitting for
a while but is probably a burnt exhaust valve or bad valve guide.  You can
try a fuel additive to see if it will clean it up and get better.  Was the
engine cranking over smoothly and evenly on all cylinders when starting?
That is a good sign of uneven compression also.  Plus, how many rpms were
you having the motor crank with the gauge installed?  I usually do 6 but if
you are checking a low cylinder you may want to try 5 or 4 because the
faster cranking can cause higher compression than normal.  If it is running
smoothly, then it must be sealing good enough for it to run halfway decent
but is probably short lived unless you get lucky and clean out some carbon.
How many times did you check it?  I have noticed that the gauge wasn't in
just right or connected just right so I ALWAYS do low cylinders 2 or 3
times.  HTH!!

Dave

compression on the new 16v rocc, which though it has more mods than my old
2l/2l head combo, seems quite a bit slower. i got:

215/215/170/215

i don't think the scale is accurate, but the 215's are what i got on the
"old" newly rebuilt engine, so i assume they are really in the 180-190
range. cylinder #3 is barely, if at all, out of spec (>44 psi below other
readings). when i crank it though, it doesn't rise as fast on the first
crank as the others. sometimes it doesn't move till the second crank.

tried a wet compression test, but i think it was useless since the readings
were above the gauge's scale (~300).

i'm thinking a stuck valve maybe, broken piston ring, or headgasket? the
engine supposedly has 34k on it (mods below), and is super quiet/smooth for
a scirocco 16v. no evidence of headgasket leak.  anyway to a) find out for
sure short of pulling the head, and b) unstick the stuck valve, if that's
what it is?

lastly, stupid question, but how much of a performance issue should these
readings be? thanks,

-michael
new 87 16v scirocco with: 1.8 bottom bored/stroked to 2l, 1.8 head with euro
intake, fuel enrichment, tt header/ss exhaust.

old 88 16v: 2l bottom/2l top. stock dp/cat, tt cat back.

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