Carbon & Exhaust Valve

[PA1195]

Re: Carbon & Exhaust Valve

Gary, I have been running Phillips XC20W50 per recommendation of my AI. A few years ago I had a C150 with a C200 and used Aeroshell 100 in summer and 80 in winter. I'm having trouble wrapping my head around the Phillips same weight for winter and summer, maybe I'm just old school and ignorant? Saveral have mentioned leaning. Since my Tcraft and most do not have a mixture control I assume you mean you adjust the mixture at the carburetor twice a year?

Thanks,

Darrin

Hi Darrin and thanks for the comments re oil. My experience with that oil is limited but ok. I have seen the oil pressure fall off after ~20 hrs use, and assume it's due to shearing in the accessory case (gears/pump), some loss of viscosity improver effectiveness, and possible dilution with combustion byproducts or fuel over time. If you like by all means it use it. Monitor your spark plugs and exhaust for soot in case it tends to burn some oil more than a single viscosity 'might'. It's a 20W oil that thins but not as much as a single grade at high temps due to additives.

I have a Marvel carb and lean to peak rpm whenever on the ground. Dropoff at mixture cut is ~25rpm and I adjust the idle mixture seasonally...out 1/2 turn in the winter; in the same during the summer.

Marvel carbs usually have an accelerator pump that ads additional fuel when the throttle is quickly opened, Strombergs don't (or at least those I had didn't). Using carb heat when opening the throttle will richen the air fuel mixture via less dense heated air being ingested and may minimize stumbles.

Gary

[M Towsley]

Re: Carbon & Exhaust Valve

Darrin,

Depending upon the carb they have on their particular engine they may be able to lean like 'conventional' engines. The Stromberg NS-A3A1 on most of these A-65's can have a mixture control, but it does not become really effective until over 5,000 feet. Most are wired in place. Search on here for much more information regarding the Stromberg's mixture 'quirks'. You cannot lean on the ground with this model of Stromberg, it will just kill the engine as you try to apply throttle.

[dkenney1]

Re: Carbon & Exhaust Valve

Thanks Scott. As a new owner of an old design C-85 (now newly stroked) I'm going to try and minimize running problems. My preference is 100LL diluted to 20-25% with regular mogas, straight weight W80 (Shell has been good for me), periodic borescope and valve examination, leaning when full rich not needed, and 75% power in cruise.

I've had two incidences of valve carbon in 4-cyl Lycomings causing sticking. Both in flight that were intermittent but of long enough duration to subsequently compromise the associated cam lobe and lifter body faces. It gets expensive real quick when they loose surface hardnesss and start spalling and rolling metal. Both were with multi-grade oils, and while it may have been coincidental, it soured me on that product. Corrosion was also indicated even though the engines were flown frequently.

On the other hand I flew three Cont IO-520's to TBO and never had to pull a cylinder with straight weight oil or had excessive lead fouling indicated by the overhaul shops. Again it may have been coincidental but proper multi-cylinder EGT management was routine.

Gary

Gary, I have been running Phillips XC20W50 per recommendation of my AI. A few years ago I had a C150 with a C200 and used Aeroshell 100 in summer and 80 in winter. I'm having trouble wrapping my head around the Phillips same weight for winter and summer, maybe I'm just old school and ignorant? Saveral have mentioned leaning. Since my Tcraft and most do not have a mixture control I assume you mean you adjust the mixture at the carburetor twice a year?

Thanks,

Darrin

[PA1195]

Re: Carbon & Exhaust Valve

Thanks Scott. As a new owner of an old design C-85 (now newly stroked) I'm going to try and minimize running problems. My preference is 100LL diluted to 20-25% with regular mogas, straight weight W80 (Shell has been good for me), periodic borescope and valve examination, leaning when full rich not needed, and 75% power in cruise.

I've had two incidences of valve carbon in 4-cyl Lycomings causing sticking. Both in flight that were intermittent but of long enough duration to subsequently compromise the associated cam lobe and lifter body faces. It gets expensive real quick when they loose surface hardnesss and start spalling and rolling metal. Both were with multi-grade oils, and while it may have been coincidental, it soured me on that product. Corrosion was also indicated even though the engines were flown frequently.

On the other hand I flew three Cont IO-520's to TBO and never had to pull a cylinder with straight weight oil or had excessive lead fouling indicated by the overhaul shops. Again it may have been coincidental but proper multi-cylinder EGT management was routine.

Gary

[Scott]

Re: Carbon & Exhaust Valve

I admit that when I was turning wrenches full time, all these engines were running on 80/87. Can't say that there was any noticeable difference as 100LL gradually became the only option other than car gas, ie the old continental suffered from periodic sticky valves before and since 80/87.

One of the discouraging things about general aviation is that comparatively very little progress has been made in terms of engine development due to the absence of a sound business case and various court decisions over the the last 50 years. So while all forms of non-aviation engines benefit fro new alloys, various electronic controls and in many cases bullet-proof reliability, we're still using all the 1930-50 materials and technology. Think about it, cars, outboards, motorcycles haven't has contact breakers for about 35 years, yet we're flying around with what amounts to 1920s farm tractor technology!

If development had continued we likely wouldn't have any of the reoccurring problems, but manufactures who did continental to develop their products ran into troubles in the courts. The argument was the a change in design, confirmed their product was defective beforehand. Manufactures lost big time and even then the potential GA market was too small and too risky for any real profit potential. So here we are with our simple old engines that the manufacturers and regulators hope won't last, but we keep fixing them and flying em complete with all the old quirks.

Yes all the valves a supposed to rotate on the continentals( and I think most other engines). This is achieved simple by grinding the rocker tappet at a slight angle. A problem occurs when the rocker wears (another weakness) and eventually the valve stops turning.

[PA1195]

Re: Carbon & Exhaust Valve

Yes absolutely. Anything to displace moisture and oxygen even just plain clean engine oil. Unfortunately if you have a sticky valve when you put the engine in storage, it will likely be just as sticky when you return the engine to service

In the world of air cooled motorcycles (I've had 53 since 1960) carbon formation is also an issue, but valve sticking is less than aged aircraft apparently experience. Part of the disparity may due to fuel (currently the lack of lead additives), and the use of detergents and soluble anti-wear components (zinc-based and Moly). I won't go into a discussion of the difference between the designs, just say that a stuck valve in a BMW Airhead (two cylinder horizontally opposed) is fairly rare. Modern motorcycles use hardened exhaust valve components that no longer require lead in fuel. Motorcycles (like Harleys) can reach head temperatures in the mid-300F range and oil temps in the mid-200's just like aircraft.

One method motorcyclists employ is to steam away deposits...ingest either water or a water/alcohol combo while running. Another is to add a compatible solvent to the oil to dissolve and suspend them in the lubricating oil. Such methods are not approved by regulatory agencies for aircraft as far as I know.

One thing aircraft cylinder manufacturers have done is employ an exhaust valve rotation device (ECI has a patent, there may be other methods like offset or off-camber ground rocker arms) in an attempt to turn the valve and consequently prevent the accumulation of deposits on the seat and guide.

Edit: I use straight weight oils in aircraft engines of old design. Looking back at mine (not always good with multi-grades...carbon, valve sticking, camshaft/lifter body failure) and asking older pilots about their experiences with oil related issues, it seems to me that some of the problems we're discussing may have increased with the advent of multi-grade lubricants. This is not an oil thread but it's been my choice to eliminate one potential source of an engine problem for that reason.

Gary

[Scott]

Re: Carbon & Exhaust Valve

How about the periodic cold application of some elixir like Aero Kroil or PB Blaster? The open valves are exposed through the spark plug holes, intake and exhaust ports, and the upper stem under the valve covers.

I've used Kroil on motors to penetrate and prevent corrosion and seizing while stored. Spray some on, rotate the innards, repeat as required.

Edit: Another product? http://www.sharpshootr.com/carb-out/

Gary

Yes absolutely. Anything to displace moisture and oxygen even just plain clean engine oil. Unfortunately if you have a sticky valve when you put the engine in storage, it will likely be just as sticky when you return the engine to service

[3Dreaming]

Re: Carbon & Exhaust Valve

Never let the facts get in the way of a good story ( Mark Twain)

Ass soon as I have facts instead of opinion to compare with the anecdotal evidence I will make sure the facts don't get in the way.

[PA1195]

Re: Carbon & Exhaust Valve

How about the periodic cold application of some elixir like Aero Kroil or PB Blaster? The open valves are exposed through the spark plug holes, intake and exhaust ports, and the upper stem under the valve covers.

I've used Kroil on motors to penetrate and prevent corrosion and seizing while stored. Spray some on, rotate the innards, repeat as required.

Edit: Another product? http://www.sharpshootr.com/carb-out/

Gary

[Scott]

Re: Carbon & Exhaust Valve

No I didn't miss it

We could ramble on about the claims made by additive manufactures to see that some are clearly BS, some are written in a way to be ambiguous at best, misleading more likely, and some are even true! (though they tend to be generalizations).

So, for example, let's look at what the statement actually says. "needs to withstand the heat and combustion of the fuel without burning" is true. Note that it doesn't say it will. The promotional material for these and other quick-fix products is full of statements like this. The statement is true enough, but the suggestion is not.

Synthetic or not it won't survive four stroke combustion in any appreciable beneficial way and even if it does it still has to somehow reach and perform miracles on the exhaust valve/stem/guide.

Perhaps you missed this part about some new synthetic oils.

"It needs to withstand the heat and combustion of the fuel without burning"

& yes I feel good knowing I'm getting at least some form of lubrication to the base of the exhaust valves,
as I'm sure some guys feel good about running MM additive.
It's really hard to dismiss success

[senior]

Re: Carbon & Exhaust Valve

Perhaps you missed this part about some new synthetic oils.

"It needs to withstand the heat and combustion of the fuel without burning"

& yes I feel good knowing I'm getting at least some form of lubrication to the base of the exhaust valves,
as I'm sure some guys feel good about running MM additive.
It's really hard to dismiss success

[Scott]

Re: Carbon & Exhaust Valve

Point taken.
It's all relative. Two strokes are incredibly tough engines and are capable of producing much mor horsepower per Cc and per kg than four strokes.

I'm a fan of two strokes. The point is however that two stroke eject unburnt fuel and oil out the exhaust, normally aspirated four strokes do not (appreciably) . Two strokes must have oil in the fuel or inject it in the induction system otherwise they will self destruct. Four stroke combustion is much more complete and any four stroke developed to the same degree as your Ski-doo example will always achieve more complete combustion over a wider range of rpm. Putting an additive in the fuel that will just be incinerated in the combustion Chamber seems a little pointless to me, particularly when you know it will contribute to carbon deposits.

But people are flesh and emotion not machines, so there's always going to be subjective considerations. Flying is no fun if you don't feel good about your engine. If your favourite fuel additive makes your more confident in your engine then it has value and the realities of combustion don't really matter.

[senior]

Re: Carbon & Exhaust Valve

" In terms of power, well we don't care too much about fuel economy. This fundamental reality of the two stroke cycle is why they burn far more fuel and are becoming a thing of the past in terms of environmental responsibility."

Scott: Seems you way of thinkin is based on your experiences formed a while ago.
In the world of smowmo's the last 10 yrs the fuel mileage king among the 120hp class including numerous 4 strokes has always been the Bombardier Ski-Doo 600cc two stroke. Yes it does struggle a little more to control emissions but it has met the new 2016 stringent standards! There's still a number of other 2 strokes still in the industry meeting the emission & fuel mileage demands of the public. Oil to has been constantly under development, I remember the original mix for my 1st Ski-Doo was 1qt of straight 30 motor oil to 5gls, yes it smoked, but a pocket full of plugs would take you for a good ride, then 2 stroke oil came out & it has constantly refined & still is being refined.

But don't let new devlelopments get in the way of your good story of bygone years

[Scott]

Re: Carbon & Exhaust Valve

Never let the facts get in the way of a good story ( Mark Twain)
Hey the bottom line is if it gives you peace of mind, it works.
One way or another someone's going to have to fix it right eventually

[3Dreaming]

Re: Carbon & Exhaust Valve

You can say all you want about MMO and how it can't work, and the problem would have went away even if you hadn't put it in there. I am not going to argue the science of it, but I have seen to much anecdotal evidence that it does work. You can say it was coincidence if you want, but I have seen problems come and go that seem to follow the use/non use of the MMO.