?Sticking Valve or Carb Ice?

[ginbug92b]

I would replace ALL springs, intake and exhaust. Now that you said that the overhaul wasn't complete, (same cylinders and springs re-installed) I am leaning even more that your problem is valve springs.

[n2582d]

I've got a Triumph Spitfire. ... Thank God Lucas didn't get into aviation...

Positive ground depends on proper circuit functioning, which is the transmission of negative ions by retention of the visible spectral manifestation known as "smoke". Smoke is the thing that makes electrical circuits work. We know this to be true because every time one lets the smoke out of an electrical circuit, it stops working. This can be verified repeatedly through empirical testing.

For example, if one places a copper bar across the terminals of a battery, prodigious quantities of smoke are liberated and the battery shortly ceases to function. In addition, if one observes smoke escaping from an electrical component such as a Lucas voltage regulator, it will also be observed that the component no longer functions. The logic is elementary and inescapable!

The function of the wiring harness is to conduct the smoke from one device to another. When the wiring springs a leak and lets all the smoke out of the system, nothing works afterward.

Starter motors were considered unsuitable for British motorcycles for some time largely because they consumed large quantities of smoke, requiring very unsightly large wires. It has been reported that Lucas electrical components are possibly more prone to electrical leakage than their Bosch, Japanese or
American counterparts. Experts point out that this is because Lucas is British, and all things British leak. British engines leak oil, British shock absorbers, hydraulic forks and disk brake systems leak fluid, British tires leak air and British Intelligence leaks national defense secrets.

Therefore, it follows that British electrical systems must leak smoke. Once again, the logic is clear and inescapable.

In conclusion, the basic concept of transmission of electrical energy in the form of smoke provides a logical explanation of the mysteries of electrical components especially British units manufactured by Joseph Lucas, Ltd.

And remember: "A gentleman does not motor about after dark."
Joseph Lucas "The Prince of Darkness" 1842-1903

A few Lucas quips:
The Lucas motto: "Get home before dark."
Lucas is the patent holder for the short circuit.
Lucas - Inventor of the first intermittent wiper.
Lucas - Inventor of the self-dimming headlamp.
The three-position Lucas switch--DIM, FLICKER and OFF. The other three switch settings--SMOKE, SMOLDER and IGNITE.
The Original Anti-Theft Device - Lucas Electrics.
If Lucas made guns, wars would not start
Back in the '70s, Lucas decided to diversify its product line and began manufacturing vacuum cleaners. It was the only product they offered which did not suck.
Q: Why do the British drink warm beer?
A: Because Lucas also makes refrigerators.

[mrpibb]

I've got a Triumph Spitfire. A drip under the engine, transmission and rear end means they've got oil and good to go! Thank God Lucas didn't get into aviation...

Oh contrar my friend, there are a many Airbus products in the skies sporting systems designed by lucas aerospace.

[GAHorn]

[...Oh contrar my friend, there are a many Airbus products in the skies sporting systems designed by lucas aerospace.

That explains it. (Why Airbus is such a dismal airplane.)

[fangzz]

New Data.

Thought that perhaps the baby step, non-invasive peening of all 6 exhaust valves had solved the problem. Also begun using some MMO in the fuel. We’ve flown 3.5 uneventful hours since, being very careful to always have an escape route, until we're sure the problem is finally resolved. Yesterday, toward the end of a one hour flight, the classic symptoms showed up. No symptoms until beginning descent with a power reduction, and there she went. But, here’s some new info.

Close to home, and at altitude, we looked at several things to shed light on what might be the cause. Dove and accelerated. Noeffect. Increased power, decreased power. Nothing. Noticed that max rpm was about 2400 without carb heat engaged. This was new and different and afforded a good measure of maneuverability and airspeed. Still slightly rough engine and reduced power and response. Checked mags, again, nothing. Then, I pulled power to idle to begin a glide to touchdown. Bingo. Resolved immediately. That may be coincidental, but in any case, that was the shortest duration of any episode except the first one last winter, which was mistaken as carb ice. Could also be the MMO. Normal throttle response til shutdown. Hopped out to see if I could detect a cool valve cover. Nope. All same, best I could detect.

Any new ideas?

Have ordered an Insight G1, 12 point egt/cht analyzer and should have it flying in a week and a half.

[Bruce Fenstermacher]

By peening you mean you removed the valve covers and smacked the exhaust valve stem with a rubber mallet to cause the valve to rapidly open and close? If so this might nock off or crush carbon from the valve set and valve that could be holding a valve open causing an air leak during a compression check but I can not see it having any effect on a sticking valve. The MMO might help but won't cure it.

Have you checked your carb for a one piece venturi properly installed?

[fangzz]

You got it Bruce. Just whacked them firmly. They weren't leaking, but we're grasping for straws here. Every thing looks and behaves so well..until it doesn't. She went about 225 smoh before the thing started showing up, and as I've said, first mistook it for carb ice. It's still rare, but it needs to be never. Had an episode in the Spring on my cross country (thinking carb ice) and it didn't show up for the about15 flying hours. We were burning 100LL on the way up here, but I don't think it has anything to do with it one way or the other. I'm less convinced it's a valve now. I've actually begun to think fuel flow, but strainers are clear and gascolator was inspected and cleaned up during annual in April, just prior to the long trip. It obviously has something to do with a reduction from cruise power to descent power and some associated reduction in pressure or vacuum or something. Can't say for sure it's not a valve, but after the analyzer install (12 point) in a week or so, I'll know for sure if it is or isn't.

[blueldr]

Have you ever had the carburetor off and looked up inside the intake manifold in the oil sump to see if there is a possible malfunction up in there? It seems to me that I remember a splitter or some sort of divider up in there.

[fangzz]

Sure haven't. But, carburetor is getting higher on my radar, after the engine totally recovered after going to idle, beginning descent. But, could something like you're thinking be so darn intermittent? 3-10 hours between?

[ginbug92b]

When I had my problem I swapped out my carb with a KNOWN good one, it wasn't the carb and I don't think the carb is your problem. Review my earlier posts, my opinion is still that you need All new valve springs, not just exhaust. Don't know why a lot of folks seem to zero in on the exhaust.

[DaveF]

Just in case there haven't been enough suggestions, here's another one. Check for a muffler blockage. The symptoms you describe sound just like a problem I had once, in which the internal muffler flame tube broke off and partially blocked the tailpipe. Symptoms were power loss and vibration, but intermittent, as the detritus moved around.

That was a single exhaust on a Lycoming engine with a single muffler. If this happened on a 170 you'd lose power on three cylinders so the vibration would be worse. I confess that since I own an Avcon conversion I'm not familiar with the innards of a Hanlon-Wilson or pancake muffler so I don't know if they have baffles flame tubes inside.

[fangzz]

Aryana, thanks for hanging with this thead and Dave, that sounds like a possibe!

[canav8]

Ok since you have isolated it. Now check the shaft going through the carb. check the bushings on there for leaks. Generally it will cause irregular operations at low induction pressures.

[HA]

hey Dave nice idea on the muffler innards. yes the Hanlon mufflers have internal flame baffles and a couple annuals ago I had to replace one of mine due to that problem. Although it wasn't to the point of blocking things yet so I can't verify the symptoms.

also a good idea on the posible intake leak at the throttle bushings on the carb. it would have to be pretty loose though, so definately noticable. I'm still waiting to hear that you made dead certain that the carb venturi isn't loose at all too, that would be one of my top picks.

[fangzz]

Guys, great inputs. Carb and/or muffler seem to be logical. We'll be checking those when we can get on 'er. In the meantime, since a lot of pertinent stuff is pretty deeply buried earlier in this thread, here's a consolidation and update I think might help you experienced maniacs, er, mechanics:

Engine Power loss Issue – What we know

Continental 0300A, 145 horse, 6cyl, 5 chrome, 1 steel.

Carbureted (Shebler) (DON’T know about single venturi yet; written data has a “pma V 64.” Haven’t looked at carb w/ cowling off to see if the V is there)

250 smoh, symptoms began about 200 at long intervals afterward.

compression all cyl’s good, NO LEAKING

plugs look good, no fouling

This year, mogas used, except on flight out from Florida (20 hrs with 100LL)

No additives used until this month (beginning to grasp at straws here) in an effort to halt the episodes (occurring every 3-10 hrs) –MMO

Symptoms and Conditions
Only after an hour or so of flight
Engine at full temp
At beginning descent, with slight power reduction to around 2200
Engine begins to shudder and loses power. Thereafter, max rpm about 2400 (2200 with carb heat)
Diving and accel has no effect
Mags check good
Condition lasts 5-10 minutes
Carb heat seems to have no effect
Last flight, discovered that symptoms quit when power reduced to idle (may be coincidental, this was after several minutes duration)

So far, it has resolved itself prior to landing, precluding finding a cold cylinder after landing (pointing to a valve problem)

Aryana, agree. The day we undress her to put analyzer on, we'll pull that stuff off and grab our mag glasses

Drew