Not 700 hours -- see my post above for the actual Lycoming-recommended intervals.
The wobble test detects signs of excess wear of the valve guide. Once found the only cure is a new set of guides being pressed in.
Correct, although new valves may also be needed, as the valve stems can wear excessively "neck down" as a result of wobbling inside the guides.
Sticking is a different issue.
Not necessarily. One cause of sticking can be a result of the excessive valve guide/stem wear resulting in a larger gap between the stem and the inside wall of the guide. With that larger gap, flame up from the combustion chamber can combine with oil down from the lube system to form "coke" -- a hard carbon substance. This can fill the gap between valve stem and valve guide inner wall causing the valve to stick. It's not the only cause of valve sticking, and it's not the only possible bad outcome of valve guide wear, but it's a possibility which must be considered.
Another cause can be simple sticking due to surface galling or combustion deposits (not just lead). Here will be one of the few times you will ever see me recommend foo-foo juice.
AVBLEND is the only reliable type of foo-foo juice I have found. Much too expensive BUT way, way cheaper than having to ream the guides. I use it every other oil change. ymmv
There is no reliable evidence based on controlled studies to suggest that any aftermarket oil additive will do anything to prevent valve sticking. None.
Point 1: I've always believed that Shell, Phillips, and the rest have a vested financial interest in producing and selling the best possible oil for your aircraft engine. Just ask Mobil what happens when you screw that up. Further, they do not have any vested financial interest (to my knowledge) in any engine overhaul shops or engine parts manufacturers. Therefore, I figure that if any of these additives were really useful, the big refiners would buy up the rights, put it in their own oil, and either charge more for the better oil or grab more market share at the same price once we aviators found out how much better it is. And I doubt that any of the additive inventors would find the serious offer of a major oil company for such a product too small to accept.
Point 2: I heard about a test run a while back on some car engines. An oil additive outfit was running ads showing how they added their magic stuff to engine oil, ran the engine a while, and then drained the oil and ran the engine for like 20 minutes before it seized. "See," they said, "after using our stuff your engine can run for 20 minutes after the oil is lost!" Some consumer advocate outfit duplicated the test, but this time with a control -- an identical engine with the same oil but without the additive. Guess what -- the control engine also ran for 20 minutes and failed the same way.
Point 3: If your engine is still in warranty, you should be aware that Lycoming says that the use of any oil additive (other than LW-16702, an anti-scuffing, anti-wear additive -- see Lycoming SB's 446 and 471, and SI 1409, which you can them faxed to you free by calling Lycoming at 1-800-258-3279 or 570-323-6181, for details on which engines this is allowed/not allowed/required in) is unnecessary and against their recommendations – which could void your warranty.
There is one exception to this general advice, and that’s CamGuard. CamGuard’s history lies in the development of Exxon Elite back in the 90’s. They wanted superior corrosion protection during periods of disuse, and put in a package of additives not included in previous oils like Phillips X/C 20W50 and Aeroshell 15W50. One of the folks who developed that package later left Exxon and continued work on an aftermarket additive product which would give other oils similar capability. This product is CamGuard. Tests by Aviation Consumer showed that Exxon Elite was measurably superior to the other oils in corrosion protection, but adding CamGuard to those other oils produced similar results to Elite. Adding CamGuard to Elite showed little improvement over Elite alone. My suggestion is that if your engine goes more than a week between flights, you either use Exxon Elite or add CamGuard to whatever else you’re using.
So before you go dumping anything other than aviation oil per the engine manufacturer’s recommendations into your oil system, consider all three points and some additional words noted below.
Also, if you read Savvy Aviator Mike Busch’s column “Slippery Stuff” in the February 2011 EAA Sport Aviation (
http://www.sportaviationonline.org/sportaviation/201102#pg92), you’ll see he says much the same as I’ve said above – don’t bother with anything but CamGuard, but CamGuard does appear to help.
And from engine guru Howard Fenton...
“Several years ago I finished a two-year blind study on [an oil additive].
“Using all kinds of aircraft engines from radials to flats where I had an oil analysis history prior to the owner starting to use the product and continuing on for two years as the owner continued to use the product. We measured the wear metal results over the study period and summarized them by specific engine group. Not 100% scientific but this was an independent study that I personally funded. I had no bone to pick with anybody one way or the other and the people who owned the product at that time were helpful but made no demands. I called it like I saw it.
“The net result was that the product does not hurt the engine and in a few cases (from testimonials) it seemed to help with valve sticking problems in some small Continentals and a few Lycomings. Our Tiger seemed to have a lazy valve on cold start which seemed to go away when I added the product. But, I no longer use the product and the condition has not returned.
“Now a personal opinion, if you want to spend $25.00 just do a short interval oil change and I believe you will get as much if not more for your dollars. I am also very skeptical of any snake oil that advertises using the phrase: ‘Try our unique “Engine Overhaul In A Can” 100% risk free!’
“To quote a famous aircraft engine man,(me) ‘There Ain't No Mechanic In A Can.’
“It won't surprise me to soon see its companion automotive product advertised with reference to the "FAA-approved" aviation additive. Testimonials don't turn me on and I have found that sponsors often get favorable comments. In fact, I have never known of a sponsored race car driver bad mouthing his sponsors products via the media.”
Regards,
Howard Fenton
Engine Oil Analysis
TUL
And from former oil company chemist Larry Tatsch
“Having worked in the Technical Service Department of a major oil company for 20 years, I know that every oil additive on the market is tested under controlled conditions in comparison with a company's standard lube products. Every additive tested by my company proved to be no better (but in some cases, worse) than the standard oil. Consumer Reports has also done similar testing over the decades with similar results.
“Lube oils are complicated blends of several base oils selected for viscosity and other properties, and packages of additives that include extreme pressure (EP) additives, neutralizing additives, detergents, etc. Additive packages can include as many as 10 components. There are very few secrets in blending oils, and most newer oils depend on changes to the base oils, such as synthetics, or incremental improvements in additive packages. Oil companies typically "reverse engineer" their competitors' oils to determine their additive packages - its a very competitive business.
“So much for fact. Now let’s do a little reasoning:
“Do we really believe that an oil additive exists out there that is so different that all the major oil companies have somehow overlooked it? This additive must be fully compatible with every oil made and must have no adverse effects. When added to the best oil available, it must provide advantages so significant that they are obvious in test engines. And despite its amazing performance, ExxonMobil failed to use it in its newest aviation oil!
“Does this seem reasonable? Not to me, with my knowledge of oil blending. When we see the photos of test engines, we should ask exactly what the additive was tested against. Was it the poorest quality straight mineral oil, or Aeroshell 15W-50?? And we all should realize that from Wheaties to Marlboro to oil additives, celebrity endorsements mean nothing. And finally, FAA approval merely means that the additive does no harm - not that it actually improves an already high quality oil.
“After reading Tom's summary of MMO use in oil, I have to add my comments to Ron Levy's. Besides all his sensible discussion about the actual value of this stuff, adding one quart of MMO to 5 or 6 quarts of oil HAS THE POTENTIAL OF DOING REAL HARM TO YOUR ENGINE.
“The reason: MMO has a very much lower viscosity than aviation oil. It will dilute the oil and dramatically change the viscosity of that 40 weight or 15W50, or whatever, to a much lower, but unpredictable, viscosity. Its the same as pouring one quart of kerosene in your engine.
“Our engines were built with clearances to accommodate specified oil viscosities. When you suddenly lower that viscosity, you run the risk of scuffing bearings and cams, which can lead to engine failure. It may be OK in many engines under various conditions, but at some point, a combination of temp and low viscosity will cause damage.
“So, is it really worth it to experiment with your engine using a product that has NO objective proof of performance???”
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