Date: Wed, 11 Dec 1996 14:21:23 -0800 (PST)
Sender: Vanagon Mailing List <vanagon@vanagon.com>
From: "Christopher M. Smith" <csmith@sdsc.edu>
Subject: Engine Tests Interpretation ?
Thanks for your concise explanation of the power balance test. It has
helped in my understanding of what the test does. If you don't mind,
I'd also like to get more of your thoughts related to the results
of further testing (leak down test, compression check).
To complete the story, I'll include a bity more detail on the engine's
history. The engine was rebuilt in 94'. I replaced *everything* in the
case, including push rods, tubes, hyd lifters, heads (remanufactured, from
GEX in L.A., Cal), oil pump, air flow sensor, clutch, pressure plate, etc.
All stock parts. This was my first solo rebuild. The rebuilt engine has
only 15K miles on it, about 50:50 city:highway. To qualify, city driving
were short trips around town, highway usage no daily commuting, but long
trips, 6+ hour RT excursions. Change oil/filter 600 miles after rebuild
and every 3K miles after that. It runs fine at idle and high speed (60-65
mph, I don't drive faster than this). Vehicle was driven in Nebraska (cold
Winters, hot Summers) up til' this past Summer. It's now in S. Cal. It has
a hard time climbing steep hills or long, gradual grades, but what VW
doesn't!
Power Compression Leak Leak Down
Balance Test Down Leak Spots
#1 73 48 16/100 Head Gasket, Exhaust, Rings
2 62 138 95/100 Rings
3 16 98 96/100 Intake, Rings, Exhaust
4 5 142 98/100 Rings
I do know that the head gasket on the #1 cylinder is leaking (I can
actually hear it squeak), so this easily explains the low compression and
low leak down value. This is confirmed by the finding that the pressure
loss primary site is the head gasket. I am VERY confused on how/why a
cylinder that is leaking as bad as it is is producing the
majority of the power for this vehicle (Power Balance 73).
No. 2 cylinder seems fine to me. Good compression and very little pressure
leakage.
No. 4 is a mystery. Good to excessive compression and very little pressure
leakage, yet it contributes very little, if any, power to the vehicle. My
first guess is that the mechanical innards are working fine, but that the
spark plug is not firing. This would explain the high HC (1000 ppm
pre-cat, unburnt fuel) in the exhaust. I'm going to check the
electrical/electronic components , as well as injector function. Your
thoughts ... ?
No. 3 is another mystery. Low compression (typical for no. 3 on the
air-cooled engines), seems to jive with the leakage via three separate
routes, but the leakage rate is no better or worse than No. 4 or No. 2.
This would indicate that any leakage through the valve ports has a more
deterimental effect on engine power than leakage via the rings and head
gaskets. But can this differential cause-effect account for such a lack of
power from the cylinder (as indicated by 16 power balance value) ? There
is also the possibility that the plug is not firing on this cylinder
either ? I'll perform the same tests here as I do for the No.3. More of
your thoughts ... ?
Thanks, Chris
82' Vanagon
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