I'll respond with what I've done:

Denny wrote:
: Hmm, your reported 79/80 seems excessive, even for 3 year old jugs...
: Perhaps the mechanic needs to test his differential compression rig
: against a calibrated orifice...

He used to have an old simple differential compression rig that I admit I was
skeptical of 79/80-80/80 on. The last few times has been with a brand new gauge set
with extra calibrated orifice for his own Continental TSIO-360. I believe the numbers
(also cannot hear any leaking at all through intake, exhaust, or breather tube).

: First, do a bit of investigation...
: Physically look up in the carb and see that the butterfly opens all the
: way at full throttle... Ya, ya, ya, I know that means you have to
: remove the cowling...
: If you are not sure where full open is it's actually a hair past
: straight up and down pull the bolt out of the throttle cable end and
: how it opens then put the bolt back in... Should be the same....
: Make sure the heat box flapper is tightly closed... Use mirrors and
: bright lighting...
I haven't visually verified the actual carb butterfly, but I have looked at
the rest of the system recently (and after the problem first manifested). Heater box
flapper is good, as is the rest of the air intake tube. I've
field-approved a MP gauge on it and I saw 26" MP at 3500 MSL last night.... I'd
believe that for full-throttle.

: Visually inspect the entire air intake tube for any blockage... ditto
: Fly it without the air filter to see if that makes a difference...
Haven't flown without, but new filter FWIW.

: Measure the fuel pressure at the carburetor, with an external gauge, at
: full throttle...
I've got the autofuel STC so the pumps are a bit different than stock. I've
watched the pressure carefully since insect parts found their way into a fuel line off
the right tank once... that was exciting too. At full power, power-on-stall attitude,
the pressure will drop down to 2 psi or so with the engine pump, but the electric
boost brings it back up to 4-5 no matter what. This is on the stock gauge in the
panel and is measured at the carb.

: Check the fuel level in the bowl (a biggie - this is often way off)...
Have not looked at this.

: Test run the electric pump with the fuel line dumping into a measuring
: can to ensure you
: are getting rated fuel flow...
Have not done this, although watching the fuel pressure go up/down a bit with
power and attitude make me believe that it's all OK.

: Make the mechanic prove to you that the mags are all timed at 25
: degrees... are the
: mags roughly at mid range on their adjustment slots - if all the way to
: one end you could have a worn acessory gear
I timed them myself with my mechanic there a number of times. We have also
swapped points and re-timed the internal timing of both. Before/after timing (it was
only off by 1-2 degrees ever) the problem persisted.

: Verify that the impulse cam (spark retard) is releasing after the
: engine starts...
Mag drop is normal when up to speed, so it must be, right?

: What is the difference in static rpm on L mag versus R mag?
No difference... both about 100 RPM. POH says 125 or 150 IIRC.

: Verify that the prop has the correct pitch... another biggie
Brand new, stock 60" prop when we got it. Only 4 hours on the logbook and the
plane performs by the numbers in the POH.

So, it sounds like I probably am close to being here...
: If nothing is found above, then rig up a dial indicator and measure the
: lift on each valve, could be illuminating... I wouldn't worry about
: oil in the lifters... Just do each measurement 3 or 4 times... Call
: Lycoming, they can give you the lift specs...
: If the cam looks OK then pull the rocker arms to:
: 1. See how the bushings look.. If egg shaped you are losing lift and
: power... Don't let
: some yahoo try to tell you that the hydraulic lifters make up for this
: - they do not!
I do not recall checking the dry tappet clearance when it was assembled 3
years ago. That could be off.

: 2. see if the valves are free... WIth the rocker out of the way you can
: use a lever to
: depress each valve for sticking... The exhaust are the ones to be
: suspicious of... If any doubt rope the cylinder and remove the valve
: spring and see if the valve is free...
That's what I was thinking. Ream the guides? I still need to get ahold of SB
1425 to check the procedures... cannot seem to locate it online.

: If everything mechanical seems up to specs then squirt solvent oil down
: each valve stem and work the valve up and down (WD40, Mouse milk,
: Marvel Mystery Oil, etc.) then change oil for a fill up of lightest
: weight oil you can get leave the filter as is add a can of AVBLEND
: and a pint of MMO (Marvel Mystery Oil) to the fill up, and go fly the
: heck out of it for 5 hours... See if that solves it...

: denny

Thanks... will keep all posted.

-Cory

--

************************************************** ***********************
* Cory Papenfuss *
* Electrical Engineering candidate Ph.D. graduate student *
* Virginia Polytechnic Institute and State University *
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