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1. 11:30 AM - leaning, plugs, rockers, dry tappet clearance, CHT (TeamGrumman@AOL.COM)
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| Subject: | leaning, plugs, rockers, dry tappet clearance, CHT |
--> TeamGrumman-List message posted by: TeamGrumman@aol.com
Now, did that title get your attention?
Ken at LyCon had told me that the new style Lycoming rockers have a little
higher rocker ratio. He couldn't give me any numbers, that's just what he
said. He also said it was worth a few horsepower at 2700 rpm, so, what the hell,
I'd get some. First, they do have a different part number and they are all
the same style; that is, they all squirt at the valve stem.
Changing the rockers isn't so simple. The entire valve train has to come
apart and the lifters bled down and cleaned.
While pulling the plugs I noticed the top plugs were all the tan color
commonly accepted as indicating an ideal fuel:air mixture ratio. I expected to
see
some lead in the bottom plugs after 90 hours. There was none. Not that
there was a very small amount, there was NONE. Plug gap had gone from
nominally 0.018 to 0.022. I regapped the plugs and reinstalled.
Back to the rockers. Not sure where the rocker ratio was changed in the
geometry of the rocker, but all push rods had to be refitted to get the proper
dry tappet clearance. I also needed to get two LONGER (#36) push rods. I
expected, given some wear-in on new valves, that some of the play would be taken
up and the box of shorter push rods that I have (I have about a dozen #35s)
would suffice. Not the case. I did manage to get all the the exhaust to
around 0.060 +/- and the intakes to around 0.040 +/- on their clearances. It's
unlikely that I'll notice any difference in the engine.
On the last flight, before changing the rockers, the #3 CHT started bouncing
plus or minus 50 degrees. I suspected the probe and ordered one. While
putzing around the #3 cylinder, I noticed an ever-so-slight amount of exhaust
stain near the outside stud/nut. I wiped it with my finger and thought I saw
a
crack. After removing the exhaust riser, it was definitely cracked. The
crack on the inside was obvious. Fortunately, Knisley Aircraft Exhaust Systems
is just down the road.
I suspect the variation in CHT may have been caused by the high frequency
vibration due to the crack. I can only wonder. I replaced both the riser (I
got a new one, I still have the cracked one) and the probe.
Time to go to work.
Gary
PS, it's wonderful being here in Auburn and finally off that GD desert.
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