View Full Version : Performance Air in Boise
07-11-2004, 01:47 AM
Talked to Steve Tubbs(?) at Performance Air, inc. in Boise Friday about my chronically hot O-320. He does a lot of cub work and knew more about cooling mods on cubs than anyone else I've ever talked with. He gave me a list of things to check and hit a home run, as I found one of the big reasons why it runs hot, and doesn't seem to have the power of other cubs....I will follow up in a week or so with numbers in the 'high CHT' thread as I get the motor modified and test for results. :D :D :D :D :D
07-11-2004, 09:35 AM
I met Steve and his son in Caldwell several years ago. They were very friendly and had a really nice shop. Can you relate his list of things to check?
07-11-2004, 11:14 AM
Just waiting for someone to ask!...he said to check that I didn't have a dash-12 carb, as it tends to lean out the rear cylinders, but especially check to see that I didn't have the conical throat air inlet to the intake manifold, as it forms a ledge after the carb which causes power loss and leaning of the rear cylinders. (Which is what I found) Lycoming makes an adaptor which drops in...(anyone know where to get one?)(cheap?) Also, measure the valve lift and see if I had a cam problem. (Haven't done that yet)
The throat size of the MA4 (-32) carb is about 1 13/16 inches diameter, and the opening into the manifold is about 2 1/4 inch diameter, almost a half inch mismatch! My guess is, that the bozos who put this engine in, ordered the wrong dash number engine, or got a 'deal' somewhere, and didn't even notice the size mismatch.(This might be a cherokee engine, designed for that MP5 pressure carb) When it was rebuilt in '97, after a prop strike, the shop didn't notice it either. This has only cost me about three cylinders.....and a heckuva lot of stomach acid.....fob
07-11-2004, 11:37 AM
07-11-2004, 11:49 AM
This might be the time to mention this....a friend of mine forwarded an e-mail to me concerning a discovery that the BD-4 boys had discovered on an engine with hot cylinders(#2 and 3) LF and RR...they noticed that the heat problem moved with the cylinders being swapped around the motor(to cool cylinder positions). Upon inspection, they saw that the heat fins between the head and the rocker box (about six of them) were almost totally blocked down inside by flash at the mold separation line.
Careful filing with needle files lowered the cht's on these cylinders about 40 degrees(F)! I checked mine, and sure enough, the hottest cylinders had the most flash, and were blocked about 60%. After an hour of filing on my hottest, I flew it, and discovered no change!!! I think now that the beneficial effect was lost due to the other problem mentioned above....namely, the carb opening mismatch... I sent this e-mail to Steve at Performance Air in partial payment for the immense favor he did for me....send me an e-mail address, and I'll forward it...
Another thought, the flow rate of air through a heat exchanger has an optimum value. Too fast, or too slow, will reduce efficiency. So don't go nuts with the filing, some roughness or restriction may be desirable. Also remember, I'm not a mechanic...ignore everything I say.
In theory, theory and practice are the same; in practice, they aren't.
07-11-2004, 11:51 AM
Dig, I guess the correct term would be a tapered riser....fob
mmmmmm...found this thread from a few years ago....
07-11-2004, 01:05 PM
I didn't mean to imply that Performance Air did my rebuild in '97, (it was SP Aircraft in Boise, I do most of my crashing in Idaho, it seems) Anyway, I just need the adaptor, anyone know where to get it and how much??? It looks like from the link, that the sump is the wrong type for my A2B engine:
The millstones of the gods grind slowly, but they grind exceedingly fine....
07-11-2004, 01:35 PM
Here's another piece of the puzzle:
"The carburettor, part number IO-3678-12, was the subject of Lycoming Service Bulletin No. 258, issued 29 May 1959. The Service Bulletin states that some aircraft have experienced rough engine operation due to an excessively rich mixture in the cruise power range and recommends that the carburettor be replaced with a "-32" model."
.... but, you need an adaptor, right?
"Precision" is the "NEW" owner of the M-S Carbs. Why don't you tell us the exact Model and S/N of your engine. also it would be hard to put a "Cherokee" sump on an A2B engine without a lot of modification.
07-11-2004, 08:05 PM
engine is a O-320-A2B TC 274 serial RL-50323-27A
80 oct 2700 rpm at 150 hp 25 deg spark
with a 2 1/4 in intake riser diameter(-A2A?)
carb is an MA4xxxxx 1 13/16 in throat (label was damaged)
serial A 37 17381
The cherokee bit was speculation...apparently the -12 carb took
the larger intake riser diameter(another guess)
07-11-2004, 09:42 PM
Natch, I didn't get the number of the sump....tomorrow night at the earliest, have to work tomorrow, and may not make it to the airport....it's a safe bet that they don't match....
07-12-2004, 11:52 PM
Called Lycoming this morning....the part number of the riser
adaptor is OS-5372-1....the dowel pin that holds it in is
STD 798 and the gasket is 66224. All this is described in
SB258. The local distributor can get it in three days for 138$$...
a good deal, in my mind... I'm thinking that the wrong sump(for an -A2A engine) got put on when my crank was being replaced in '97....these are the same guys that welded my left landing gear on crooked and adjusted the tire pressures to try to hide it......
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