Engine sputtering and low static RPM?!

[170C]

"Idling at 800 RPM and pulling the mixture without advancing throttle is my preference."

What am I missing here George? Didn't you just state that advancing the throttle while pulling out the mixture was putting raw fuel into the engine which could leed to more lead being left on the plugs?

[jrenwick]

Is there a procedure for "aggressive leaning"? Is it the same as in the owner's manual, but simply running full-rich as little as possible, or is it a different leaning technique? What is the definition of this often-used-but-seldom-defined term?

[GAHorn]

"Idling at 800 RPM and pulling the mixture without advancing throttle is my preference."

What am I missing here George? Didn't you just state that advancing the throttle while pulling out the mixture was putting raw fuel into the engine which could leed to more lead being left on the plugs?

I guess I don't understand your confusion, Frank. What are you specifically not understanding?

Is there a procedure for "aggressive leaning"? Is it the same as in the owner's manual, but simply running full-rich as little as possible, or is it a different leaning technique? What is the definition of this often-used-but-seldom-defined term?

The Owner's Manual gives a good description for carburetor-equipped, non-EGT, fixed-prop technique. Set cruise power, slowly lean until first indication of rpm-loss, enrichen only back to max rpm...no more. (Some folks seem to think if enrichening back to max rpm is good...then enrichening a bit more is better. For purposes of eliminating lead fouling, Not true of course, for "aggressive" purposes. Remember, leaning aggressively is unlikely to injure the engine at power settings at/below 65%.)

With a constant speed prop an EGT or engine analyzer is virtually required equipment for accurate leaning. Lean-of-Peak is probably the best current thinking on that subject, and multi-probe/analyzers are necessary for that, but beware of some specific engine models mfr-cautions on that.

[Bruce Fenstermacher]

It's not a good idea to "lap" valves which are not leaking, and it's never a good idea to do it with the cylinder on the engine.

If valves don't leak then there is no need to remove material from engine parts which lapping valves and seats does, I agree. And to subject the cylinder to the grit and dirt lapping requires "just because" is foolish. But I assure you that a light lapping of a valve and seat can be successfully accomplished with the cylinder installed. You must work neatly and with the precision and cleanliness of a surgeon however. I would prefer the cylinder not be installed but I'm not going to remove it for a touch up lapping. It is a judgement call.

Aggressive leaning to me means leaning at least by the book method at every available opportunity without exception.

I say I don't lean aggressively because I have never leaned in a taxi, and I rarely lean by the book method. I do lean the engine of my 170 when I remember to, from full rich to something less than full rich and I may not even see an RPM rise. In reality I may not actually be leaning at all. I should add that I fly at sea level or close to it and leaning has never been required for performance.

[170C]

After rereading my post & yours, I see the difference is that an IA told me to run the rpm's up (to about 1200), then pull the mixture & as the engine coasts down from lack of fuel to advance the throttle to full open. Your method appears to stop the plane, let it idle for a short time, then pull the mixture & advance the throttle. Your method may not put raw fuel into the intake as much, if at all, than doing so from a higher (1200 rpm) setting. In either case, what does opening the throttle as the engine shuts down do?

[jrenwick]

The owner's manual for a B-model says, in the "after landing" part of the Operating Check List on p.26:

"(3) Stop engine by pulling mixture control knob to full lean position. Do not open throttle as engine stops."

The previous step has you idling at 800 RPM as necessary to allow the engine to cool down if you've been taxiing a long time. If the throttle is at idle when you pull the mixture knob, the engine will take longer to stop, because the mixture control does not close the idle jet.

The carburetor has an accelerator pump: a device that squirts a jet of fuel into the manifold as the throttle is opened. This prevents the engine from hesitating due to a sudden increase in manifold pressure before the additional fuel gets to the cylinders. If you open the throttle as the engine stops, the accelerator pump will squirt gas into the manifold, resulting in some unburned fuel remaining in the cylinders as the engine stops.

[Bruce Fenstermacher]

After rereading my post & yours, I see the difference...... Your method appears to stop the plane, let it idle for a short time, then pull the mixture & advance the throttle.

Frank, I've reread George's comments and he NEVER suggests advancing the throttle after the carb mixture is pulled full lean to kill the engine. In fact he says NOT to do it several times.

[170C]

Guess I needed to reread it more carefully Bruce You are correct. I haven't used the method the IA suggested in a year of so and am glad to know that I haven't been creating more problems by doing so. Thanks

[Hattrick]

This discussion reminds me that diagnostics need to be addressed from a logical starting point and progress thru to a logical conclusion. Some basics were skipped as assumptions were adopted without proof.

Example:
Stuck valves can be detected by simply "pulling the prop thru" and listening to the exhaust/intakes hissing in conjuction with loss of compression on the affected cylinders. This would likely have brought us to the diagnosis very early. (I often fail to acknowlege some owner's level of experience and then fall into this trap.)

George,
Thanks for your input... I actually did pull the prop through before deciding to pull the rocker covers off and had a hard time feeling the lack of compression in the prop pull through (due to lack of experience) although I'm pretty sure I did feel it. Of course after pulling the covers we found the stuck exhaust valves in the open position.

Today we spent about 3 hours pulling off the 3 cylinders and reaming the guides for the exhaust valves and cleaning/lapping the valves themselves... The two valves were very resistant to coming out of their guides and we need to use several taps with a mallet to drive them through the guides and out the cylinder. Now that we have reamed the guides they slip in very easily. Hopefully this work (essentially a top overhaul on the left bank) will prolong anything like this happening again anytime soon.

Saturday we will be putting everything back together with new gaskets, nuts, and even some studs that needed replacing. All in all I'm expecting about $500 out of pocket for everything maybe less maybe a little more.

It sucks I had such bad luck so early into my ownership of my 170 BUT on the flip side I really enjoyed getting dirty and taking everything apart today and truly seeing how everything is put together and works. That being said I REALLY hope I don't have to do this again for a long time to come.

[johneeb]

.........
Today we spent about 3 hours pulling off the 3 cylinders and reaming the guides for the exhaust valves and cleaning/lapping the valves themselves... The two valves were very resistant to coming out of their guides and we need to use several taps with a mallet to drive them through the guides and out the cylinder. Now that we have reamed the guides they slip in very easily. Hopefully this work (essentially a top overhaul on the left bank) will prolong anything like this happening again anytime soon.

Saturday we will be putting everything back together with new gaskets, nuts, and even some studs that needed replacing. All in all I'm expecting about $500 out of pocket for everything maybe less maybe a little more.
............

Mark,
Be very carefull turning the crankshaft while you have all the crankcase through bolts removed. There have been instances, noted here and Cessna Pilots Assoc, of main bearings shifting during this condition. A good technique is to leave the through bolts in place and use washers, to compensate for the missing cylinder flange, and reinstall the nuts while doing any crankshaft rotation.

[Bruce Fenstermacher]

Yes it does suck you had to do this so early in ownership. That is the first think I thought of.

[canav8]

What I find ironic ,and like George, I should have just listened before commenting. It amazes me how you go from purring like a kitten to giving kitty a bath and then pulling three jugs. It doesnt just do that. Sorry but Mark should have been more specific. I learned from this. John brings up a very important point. DO NOT SPIN THE CRANK with crancase bolts loose. The damage I have seen from it will make a wallet bare! D

[DaveF]

Don't beat yourself up about it, Mark. I've always found that the first year I own an airplane is the most expensive. In this case your hand was forced, but usually there are things you want to fix just to bring them up to your standards. I bought my 170 from good diligent guys, but I still found tailwheel problems, some fuel seeps, and old hoses.

[Bruce Fenstermacher]

Doug that is exactly the way as stuck valve is. Running like a clock one minute. You shut down and start up and she's running horrible. Like on 5 cylinders.

I wouldn't have been so sure of my diagnosis except the EXACT same thing happened to me. Running fine, washed the plane, ran like crap. It took me 4 days to diagnose it the first time on my plane and the valve was stuch hard open with NO compression in that cylinder. Basically all those things you all suggested I did over 4 days till I tripped on the open valve at the suggestion of a friend who didn't know what a stuck valve was but had heard the phrase at one time.

When Mark said running fine, washed the plane, running like crap ON BOTH MAGS I knew it was a valve. Fact is there was probably only one stuck when he ran it but the other one stuck turning it over slow by hand. Or they both stuck open when turned slow by hand and both were sticking enough to delay closing slightly thus running rough. The fact Mark may have felt some compression on all cylinders tells me they really weren't stuck open hard when running but sticking enough to run rough.

[canav8]

Doug that is exactly the way as stuck valve is. Running like a clock one minute. You shut down and start up and she's running horrible. Like on 5 cylinders.

I wouldn't have been so sure of my diagnosis except the EXACT same thing happened to me. Running fine, washed the plane, ran like crap. It took me 4 days to diagnose it the first time on my plane and the valve was stuch hard open with NO compression in that cylinder. Basically all those things you all suggested I did over 4 days till I tripped on the open valve at the suggestion of a friend who didn't know what a stuck valve was but had heard the phrase at one time.

When Mark said running fine, washed the plane, running like crap ON BOTH MAGS I knew it was a valve. Fact is there was probably only one stuck when he ran it but the other one stuck turning it over slow by hand. Or they both stuck open when turned slow by hand and both were sticking enough to delay closing slightly thus running rough. The fact Mark may have felt some compression on all cylinders tells me they really weren't stuck open hard when running but sticking enough to run rough.

Ok, so your simple answer is: Dont wash your planes and you will never have stuck valves. There!