what is this??

[GAHorn]

My pipes are cut with a fore-to-aft slant...looks like it should produce a positive pressure on the exhaust system....Only the left stack leaves the gray residue....go figure...

John

N2786C, Ratty ole Alaska Bush Plane

One side will leave more deposits than the other due to "whirlwind" effect of the prop-blast.

[Bruce Fenstermacher]

Frank there are lots of techniques. Some have some technical basis others don't.

By comparison my C-85 powered Cub has identical cylinders as our C-145/0-300. In fact the A-65/75 found in most Cubs has very similar cylinders. Four cylinder Continental engines are essentially the same as our C-145/300 but with just four cylinders. One difference though is very few Cubs have a mixture control and those that do are pretty ineffective. You can not shut down a Cub with the mixture if you have one in any case. Cub engines are stopped by switching of the mags.

Cubs and 4 cylinder Continental engines have the same ignition system and spark plugs as the C-145/300 if they've been converted to a shielded system. Lots of Cubs and four cylinder Continental engines are converted.

So you would think that with the lack of leaning capability my Cub and perhaps with four cylinder Continentals in general, there would be a higher occurrence of lead plug fowling and valve sticking. But I have not experience that to be the case. When I remove the plugs from my Cub I expect them to look the same as those from my 170. And I've experienced valve sticking in about the same amount of hours.

Not saying you shouldn't lean your engine or lean on the ground or the shut down procedure you described does not good, just sharing an interesting observation from an aircraft with practically the same engine that can not be leaned.

[flyguy]

Miles In case you didn't know......nothing "bad" ever happens to guys with pocket protectors W.

"Sure you don't want to buy a couple of these? - Jerry (Nice suit walking down the street selling P.P.s)
"Huh?" - Unknown (man sleeping in park)
"See this? (Barry , new temp, showing off his P.P.)
"I respect a man with a pocket protector" - Betsy (attractive office worker)
"I never have arrested a man wearing a pocket protector" - Sam (Policeman in South Dakota)
"Phear the man with the pocket protector" - Jim (some kind of free software programmer)
"See this? (Barry again, showing off his P.P.)
"So what?" - Unknown (man carrying sign about working for food and God bless)
"OK, I see your P.P. but may I see your drivers license" - (Large man in police uniform)
"Wrong door, bud, trust me." - Unknown (gruff man downtown in some old building)
"It fit my shirt pocket, wow!" - Barry ( showing of his new P.P.)
"Sure it looks great, now this is my corner OK?" - Angel (Girl of the street, downtown)
"See this? (Barry again, showing off his P.P.)
"Here is a dime, call someone who cares." - (new gal from the temp agency- would not give her name)
"No, and you see that sign over there." Unknown (serious security guard when offered a P.P.)
"Sure, thanks. Would you like fries with that?" Jill (restaurant worker)
"Man I like these , I really like these, thanks man" - ( Barry again when offered a six pak pf P.P.s)

MAKENO SENTS TU ME

[hilltop170]

Say what?

[HA]

time to break out the Crown until I follow that last post

then I will have achieved enlightenment. whoops, supposed to fly tomorrow morning - perhaps I better remain part of the unwashed

[170C]

I agree with you Bruce. I am not sure what actually causes stuck valves. I have really been lucky by not having one---YET! I do try to lean as I taxi out to fly, but am remiss in not remembering to do so upon my return to the hangar. I do lean in flight with the method mentioned earlier--lean till rpm drops, then enrichen until it smooths back out/returns to the rpm prior to leaning. I also wonder why we don't hear of stuck valves in C O-470's or IO-520's

[GAHorn]

It DOES happen in larger engines. I had one once in an IO-720 that bent the pushrod and the engine then snapped the valve-head off in flight (at night) and really got my attention.

Fortunately I was already on downwind and merely idled the engine and landed.

[170C]

Yea George, but that was a Lycoming

[jrenwick]

One difference though is very few Cubs have a mixture control and those that do are pretty ineffective. You can not shut down a Cub with the mixture if you have one in any case. Cub engines are stopped by switching of the mags.

This is really a function of the carburetor, not the aircraft or engine type. My Cub originally had an A65 with a Stromberg carb. That carb has a semi-effective mixture control that won't kill the engine. In mine, it was wired full rich. When I replaced the A65 with a C90, I got a Marvel-Schebler carburetor like what's on my 170, with a real mixture control. It will kill the engine, but only if it's running something above idle speed. At idle, the engine is getting enough fuel through the idle jet to keep the engine running. The idle jet is not affected by the mixture control. The need to be running above idle for the lean cutoff to work might be the reason for advancing the throttle as you pull the mixture lean.