Subject: RE: Guzzi machinists near Sacramento, San Francisco CA?
Author: gerar-@netzero.net
Date: Mar 23, 2005, 10:45 PM
Post ID: 1718591342
Hello Patrick-
| First, how did you LOCK the engine at TDC? Air will blow the piston back down unless you have the flywheel locked in some way. |
The air compressor I used was quite small. I found that the TDC mark did
not move after I did the leak down test. I had to rotate the crank all
the way to the most advanced timing mark before the compressor would
push the piston down.
| Second, were you certain to be on TDC of the compression stroke? There is another TDC between the exhaust push and the intake suction. Can't get valid readings there. |
I am aware of that. I set it at TDC by rotating the crank at the pulley
under the front cover while holding my thumb over the spark plug hole
and waiting to feel pressure building. Then I set it at the timing mark
for the #1 cylinder and to another scratched in mark for TDC for the #2
cylinder after feeling compression develop in the #2 cylinder.
| Third, how did you "pump air" into the cylinder? Just hold a nozzle up there? Converted an old spark plug to an air jack? Built yourself a leakdown tester? |
I built a primitive leakdown tester similar to the one shown at
http://vmaxoutlaw.com/tech/leakdown_tester.htm. I could not get the
porcelain out of an old spark plug, so I used the spark plug fitting
from an old extra compression tester and used that. The gauge was
reading only 10% retained air. I sprayed down the tester and line with
soapy water to see where air could be leaking, but there were no
bubbles. I also noted the air was clearly coming out of the oil system,
NOT the valves. Granted, if I held my thumb tight over the spark plug
connector, the gauge would only show 30% retained air. That's when all
the other connectors on the tester would start blowing bubbles when
sprayed with soapy water! I suppose I should order a tester online.
Thanks so much for the offer, but I'm reluctant to drive up and back
when I can lazily punch some keys online! :)
| Fourth, that compression seems fine. I wouldn't tear into a motor that had that compression, especially if both sides were near each other. What was the difference between the two sides? Did you hold the throttle WFO during the test? |
Yes. We did the test several times. Incidently, I repeated the test
before I responded. Different compression tester, similar figures. Hmm.
I confess a certain amount of frustration with the idling. I have
rebuilt the carbs, rebuilt the distributor, set the valves, timed the
ignition, replaced the exhaust with stock pipes. It seems like I've done
everything except fix the compression, so perhaps I've got a hammer and
everything looks like a nail.
Gerard