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#11
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O-360 sticking valve update
Interesting theory, but I have a hard time believing that the oil warms up
appreciably in 60 seconds. My thoughts: The application of full power on an aircooled engine causes things to heat up very rapidly since there is little thermal inertia. On startup & taxi, the oil bypasses at the relief valve & doesn't get much access to the heat of the engine until you get to a certain point, where it really begins to remove heat, quits bypassing and then warms up quickly. The specific heat of oil isn't very high yet the heat input once things get to spraying around the crankcase are probably pretty substantial. Somewhere the intake manifold might be changing from a mixed liquid/vapor flow to an all vapor flow at a corner or an obstruction. Look up the manifold and on the carb gasket when you do the throttle plate bit. Check for loose clamps etc on the manifold tubes - but it sounds like your mechanic etc (I. e. you) are pretty well on top of things and have done that already. Q - How well did the Lycoming clearance measurement thing work? I built one but have not used it yet. Was your's per their plans? |
#12
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O-360 sticking valve update
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#13
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O-360 sticking valve update
nrp wrote: : The application of full power on an aircooled engine causes things to : heat up very rapidly since there is little thermal inertia. On startup : & taxi, the oil bypasses at the relief valve & doesn't get much access : to the heat of the engine until you get to a certain point, where it : really begins to remove heat, quits bypassing and then warms up : quickly. The specific heat of oil isn't very high yet the heat input : once things get to spraying around the crankcase are probably pretty : substantial. : Somewhere the intake manifold might be changing from a mixed : liquid/vapor flow to an all vapor flow at a corner or an obstruction. : Look up the manifold and on the carb gasket when you do the throttle : plate bit. Check for loose clamps etc on the manifold tubes - but it : sounds like your mechanic etc (I. e. you) are pretty well on top of : things and have done that already. I'll check that. Remember though, that it has done this in the summer as well as now in the "winter." Not like the forecast high of 63 degrees today could really be called "winter," but it was about 40 the last time it acted up. I'm pretty sure when I left Milwaukee at New Year's time it acted up on takeoff too... probably 35 degree late-morning after a cold-soak overnight at 25 (with preheaters on). : Q - How well did the Lycoming clearance measurement thing work? I : built one but have not used it yet. Was your's per their plans? Well, due to liability concerns, they've killed all the student-accessible machine shops. I basically had to beg the shop to chuck up the aluminum stock into the lathe and ream out the 0.496" hole. The rest of it I built with a spoon and my teeth (i.e. drillpress and hacksaw). It was a crude approximation of the tool outlined in the SB388, but it worked to extend the valve's stem. As far as measurement part, I used a dial indicator with magnetic base and manipulated it to hit the rod vertically at 2.5" from the valve guide as per the SB. I didn't build the holder doodad that goes on the rocker arm pivot rod. Not very elegant, but it did work... just more of a pain to set up and move from jug to jug. The biggest problem that I had was how much to open the valve. When it was well-seated (i.e. fully closed) the clearance was very small. One it was opened a bit, it opened up to about the limits. The SB doesn't describe how much the valve should be open. I suspect the magic Lycoming tool compresses the valve spring enough to deseat the valve, but it never says how much. -Cory -- ************************************************** *********************** * Cory Papenfuss * * Electrical Engineering candidate Ph.D. graduate student * * Virginia Polytechnic Institute and State University * ************************************************** *********************** |
#14
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O-360 sticking valve update
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#15
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O-360 sticking valve update
Your observations were discussed at our coffee-shop klatch this morning
& a new possible theory came out. A local EAAer had a factory reman Continental C-90-12F that would sag immediately post-takeoff. He wrestled with the problem for about 300 hrs before he tore it down. He found that there was insufficient ring gap and that the cylinder bores had become glazed such that they looked like mirrors. He rehoned them and reassembled & it fixed the problem completely. I too find it hard to believe, but it might at least be worth a look into the cylinders next time you have the plugs out. |
#16
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O-360 sticking valve update
nrp wrote:
: Your observations were discussed at our coffee-shop klatch this morning : & a new possible theory came out. A local EAAer had a factory reman : Continental C-90-12F that would sag immediately post-takeoff. He : wrestled with the problem for about 300 hrs before he tore it down. : He found that there was insufficient ring gap and that the cylinder : bores had become glazed such that they looked like mirrors. He rehoned : them and reassembled & it fixed the problem completely. : I too find it hard to believe, but it might at least be worth a look : into the cylinders next time you have the plugs out. Interesting. How does that cause a power sag... just extra friction? Seems unlikely in my situation since I've got chrome jugs (*already* mirror smooth except for channels), excellent compression (78-80/80 on all four), and 8 hours/qt of oil consumption. Might try to get ahold of a borescope and have a looksee though. -Cory -- ************************************************** *********************** * Cory Papenfuss * * Electrical Engineering candidate Ph.D. graduate student * * Virginia Polytechnic Institute and State University * ************************************************** *********************** |
#17
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O-360 sticking valve update
Supposedly the power sag was due to friction. I didn't witness it
myself. You probably wouldn't need a borescope. Just lower a small bulb into the cylinder in a dark room & look at the walls. There might be a scenario where your excellent compression & low oil consumption is a symptom.......! nrp |
#18
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O-360 sticking valve update
nrp wrote:
: Supposedly the power sag was due to friction. I didn't witness it : myself. : You probably wouldn't need a borescope. Just lower a small bulb into : the cylinder in a dark room & look at the walls. : There might be a scenario where your excellent compression & low oil : consumption is a symptom.......! I have a hard time believing that friction could be the culprit. If I'm losing 5% power, that 5% of ~150 hp (fixed-pitch prop at 2000'DA). If all of that 10kW is going into *friction*, something gonna fry and wear through pretty quickly. I've never considered 8 hours/qt "low" oil consumption... Probably healthy since too little can be worse than too much oil consumption. Anyway, I'll try to take a look. -Cory -- ************************************************** *********************** * Cory Papenfuss * * Electrical Engineering candidate Ph.D. graduate student * * Virginia Polytechnic Institute and State University * ************************************************** *********************** |
#19
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O-360 sticking valve update
This may be a shot in the dark, but many years ago we had a similar problem
(slight sag in power during initial climb) with the O-320 in a Cherokee-140. After some troubleshooting we determined that most of the lost power could be restored by significantly leaning the mixture. That led us to determine that the cause was a partial obstruction of the intake air path between the air filter and the carburetor, causing the mixture to be excessively rich. I don't recall what the obstruction actually was (or how it got in there) but it seems that it would be most pronounced at high power and high nose-up attitude. If you haven't done this already, next time the "sag" occurs, see if leaning helps a bit. Sorry if you have previously reported that you've already tried this. -- -Elliott Drucker |
#20
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O-360 sticking valve update
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