<VV> Engine issue
bicknell at cfanet.com
Mon Nov 29 21:05:07 EST 2010
I understand that lean mixture can cause detonation. However, the #2
cylinder is the shortest path from the carburetor and so I figured it was
the least likely to get leaned out.
From: Michael Kovacs [mailto:kovacsmj at sbcglobal.net]
Sent: Monday, November 29, 2010 6:13 PM
To: Bill Bicknell; VIRTUALVAIRS at CORVAIR.ORG
Subject: Re: <VV> Engine issue
It was like this when you purchased it. Is there a possibility that #2 isn't
getting a full charge of fuel/air? In other words a lean mixture? Could
something be restricting the intake manifold up stream of #2. This is a wild
shot, but one cause of detonation is a lean mixture.
I assume you are using the proper plugs. Sounds like you did all the right
stuff to cool the cylinders.
----- Original Message ----
From: Bill Bicknell <bicknell at cfanet.com>
I have recently acquired a 1962 Rampside with #2 piston burned from what
appeared to be detonation. All other pistons/cylinders looked normal.
After replacing the piston and honing the cylinder to clean up the aluminum
transfer, the same #2 piston became burned due to detonation. The engine
would idle fine at 14 degree timing, but with lack of power. At about 18
degree timing it seemed to run reasonably and with good power, but with
pinging noticeable when starting from a dead stop. I have replaced the #2
piston again, this time with a different used cylinder and still notice the
detonation from start, but haven't driven it much until I can learn more
about what's going on.
When I replaced the first piston, I also changed rings and bearings and
timed the camshaft to the crankshaft as accurately as I could determine.
This seemed to be a challenge. I used keyway positions checking with
machine squares. Since such advanced distributor timing is required, I am
still wondering if this is an issue. What is the best technique for this
timing operation? But why did the same cylinder position have the problem -
I have been rebuilding conventional water-cooled engines for decades, for a
while professionally, so I know engine basics but something is eluding me
here. Perhaps something unique to Corvairs. Knowing that
pre-ignition/detonation can initiate from carbon build up and/or sharp
edges, I wire brushed all combustion areas, valves, and valve cavities
clean prior to assembly. All fins were cleaned to avoid hot spots. The
sheet metal air deflectors are in place. The thermostat properly opens the
air deflector valve when the engine heats up.
Can someone help with some suggestions?
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