OK Roadster faithful, the newly identified reason for the ignition miss has
come to light. First, to those of you who suggested the leak down test: GOOD
CALL. It did however take some extra sleuthing...
So, I did the leak down, first by testing each cylinder on TDC with the
compressor set at 100lbs. The first time I did it I did not set the brake
hard enough and got my foot run over when I put the air to the cylinder. Even
with the brake set hard, it still wanted to creep even in 5th gear. Number 1
had virtually no leak down, though I am sure it is leaking some (1-3lbs
maybe). Those Total Seal rings appear to be doing their job. I continued on,
testing 3 then 4 with the same results. When I got to #2 however, air started
coming out of #3... and #4? Huh? How can that be? If the head gasket was
blown between 2 and 3, then it would make sense that #3 would hiss, but #4?
Hmmm, is my head a banana?. Continued testing, confirming again that both 3
and 4 were the same as #1with virtually no readable leak down. I could have
concluded that I had a blown head gasket, but the air coming out of #4 bugged
me, plus I was not getting any leak into #2 when testing 3 or 4. So then I
decided to pull all the rocker arms in order to fully isolate each cylinder.
That was when the issue became apparent. Cylinders 1, 3, and 4 all remained
with unmeasurable leak down, but #2 was loosing 12-15lbs. A quick listen
around to the carbs and exhaust identified a burnt (or more likely bent)
exhaust valve... hissing in the exhaust pipe. The reason I was getting air in
3 and 4 through 2 was that the exhaust valves for 3 and 4 are just slightly
open when the rockers are installed, so air leaking past #2 exhaust valve was
sneaking its way into 3 and 4 through the header.
So there you have it. I will be pulling the head shortly, and fully expect to
find a damaged #2 exhaust valve. It could be burnt, but I doubt it. More
likely we did not relieve quite enough off that piston... it was a custom job
to make them fit in the first place (Venolia forged pistons I got at Shasta
several years ago)... that is why I know my compression is 11.7 to 1... we
kept having to play with it until the head would seat down. We clayed all
the chambers to make sure the valves did not hit, but I later had the head
disassembled and reassembled by a different shop and the assembled height may
have changed just enough to contact a valve.
So, a bit of a bummer, but nothing terrible. Hopefully the head studs will
not give me too much trouble. And I can hardly wait to see what this engine
will do with all 4 hitting at 100%... heh heh heh...
Again, thanks for ALL the suggestions and thoughts. I will let you know how
it turns out!
Greg Burrows
#588 (still love her)
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