Ok lets first clear up some terminology about 2 cycle oil being "Burnt" in these engines that will dispel the confusion of what we are talking about. The oil does not get "burnt" as in the fuel being burnt/ignited to create pressure on the piston to create forward motion of the motorcycle. The carbon deposits on the piston is the product of only a minute (0.0000001%) percentage of the total oil going through the engine that oxidises and leaves some deposits. In fact I will argue it is a minute amount of the additve pack instead later.
A nanoscule of oil only as 2 cycle oils are made with ashless low deposit base fluids (POE's, PAO's and PIB's when they are not too heavy) and ashless additives. Just because the oil gets blackened by the combustion event does not mean it has been burnt like "oil" does in a diesel engine.
Imagine if ALL your oil got "Burnt" or turned into deposits you would have to clean out your exhaust and take down your engine between heats due to the carboning. To completely burn the oil you would need a compression ratio of 17:1 like a typical diesel engine. Our bikes range from around 8:1 to 12:1.
In a 4 stroke engine when you have worn rings or guides and sump oil enters the combustion spaces the oil leave greater carbon deposits (usually hard, but excessive oil is used then black fluffy deposits are laid down) as the oil is NOT an ashless oil (except for in Aero engines like your Lycoming, Pratt & Whitney in DC-3's or Cessna etc that has 2 stroke like dispersants in it to stop plug fouling up in the air) as it contains a great amount of metallic detergents and dispersants, anti wear addtives etc as it has to stay in the sump for a long time to do its work over and over again. A typical 4 stroke motor oil (diesel or petrol) has a Sulphated Ash content of between 0.8 to 1.2% which is all that is left over when "cooking" the oil in lab conditions on a hot plate at 550C. (This is duplicated inside your engine) So all you have left from 100% liquid oil is 1.2% residue that is the carbonised additive pack. Barium and Calcium detergent additives are not added to 2T oils as they will leave this residue.
To advance this point further, and bring it into perspective, why is it only a nanoscule (I made this word up) of the total oil that you see behind on the piston? It is because of the active additive package of a 2T oil is only a fraction of what its 4 stroke oils brother has inside it. On the Motul 710 data sheet it lists a specification called TBN. (Any diesel/railroad/marine mechanics out there) it means Total Base Number and on any 4T oil you buy for your car or bike it will list this. It refers to the level of detergency and alkalinity reserve contained in the oil blend to combat acid attack from sulphur in the fuel. A diesel engine oil that has to deal with lots of sulphuric acid from the fuel and has a typical TBN between 9 and 13, a petrol engine oil for cars now has between 6 and 8.
And the TBN of Motul 710 for instance is 2.1 and for 510 semi-syn a mere 1.1. This means that the formulator knows that adding too much detergency/dispersancy is a waste of money and excessive amounts wont do the job of cleaning (as the oil doesnt stay in there too long) and a % of the excess will end up as carbon on the piston and dome. So less additive is more in this case as it is a waste of money to have good unutilised additive to go out the exhaust.
In a 4 stroke engine the oil goes black because the high TBN additive collects and disperses the soot generated by the combustion that goes past the rings into the sump. 2 cycle oil goes black because of getting this soot mixed up in it as well. However I recall tests being done a long time back and a 2 stroke engine running flat out at steady throttle does not dirty its oil as bad as when we are on and off the gas resulting in incomplete combustion that generates soot. Leaner or optimum fuel ratios generate LESS soot as well. If you ran your bike down the saltflats as hard as it would go the oil coming out the pipe would almost be as clear as when you put it in. Under these conditions you would also generate less smoke. If you could condense it and collect it you could almost reuse it!
I have argued elsewhere in modern bike forums that the 2 stroke is making a resurgence for economic reasons against the expensive to run 4T bikes. If the 2 stroke bikes get developed further they may be fitted with "scubbers", particle filters on the exhausts to catch the oil vapour like modern EuroIV diesel cars and trucks now have to trap soot. Many car and 4T bike race engines have a catch can to catch any excess oil vapours from the crankcases escaping from the breathers not for environmental reasons but for track safety.
Lee Iacocca, former Ford president said, "We've got to pause and ask ourselves: How much clean air do we need?"
Ji, keep your fuel/oil tins inside your car wrapped in blankets/sleeping bags and mix the fuel in the morning and fill your empty tank prior to riding if using A747. I also saw on the weekend guys heating up their plugs with lighters and a gas torch before putting it into their bikes for starting. It was around 1C at 9AM cold start test.
I also expereinced less "out of the hole" bottom end exiting from corners on the MX track as I ran 95 octane fuel compared to 100 this weekend to test. You had to drop a gear and rev it out a bit more.
Stevo, seek out the Fuel 2 Race in Sydney that is well priced and as good as the $$$ imported ELF/VP stuff. Ring Bob the owner on 0404-347-367, he has a guy in Brisbane that handles it but I do not know who.
I highly recommend you try H1R at the richer ratios as it is a lower viscosity. You might like to try Motul 710 as well.
What you are finding with the discharge from your current oil is most likely the excess heavy PIB that you removed by hand. I mentioned in my viscosity tests how sticky the 800 was when trying to clean it off the flowstick.
The "grunge" on your piston is a mixture of burnt fuel residues but also in greater proportion the heavy PIB (tackafier) that if you jetted correctly (leaner) the hotter combustion would not have allowed the PIB to settle out like that. Bad news if you have a powervalve and get that stuff on it.. "Death-ash" that forms on the underside of the piston crown is due to excessive leaness and is more common in 4 strokes buring against the very hot piston. It does occur in a 2 stroke but less so.
Shortshifter, that Mobil Super 2 Stroke Oil back then was a very basic formulation before Mobil got into synthetic technology (They own an Ester plant in the USA so decided to value add). To get that level of cleanliness using that oil with such high levels of Brightstock and mineral oil he would have had to have spot on jetting. But talking to one guy over the weekend Castrol SuperTT was a great performer till the about 1980 when it is thought Castrol changed part of the formulation package and it left deposits. Maybe they did it on purpose to swing customers to their new TTS?!?
Graeme, Try to use any of the low to mid viscosity 2T oils on the market like TTS, Motul 710, BR H1R or Si-7 (like I used in the weekend @ 20:1) and many others in the Viscosity range of 35 to 60 centistokes @ 40C (100F). More oil leads to less plug fouling via the cleaning action of the oil, if your jetting is also right. I forogt what Eric Gorr said about how much should be left at the bottom when taking your barrell off.
Viper666, I am not particularly brand loyal these days and look beyond the labelling and stick to the philosophy of lighter oils at greater ratios. I would go out an buy perhaps 6-8 different oils that meet my philosophy. I used half the BR Si-7 bottle, then I will use the TTS and the 710 I bought the other day. Riders learn first off from what works off other riders, but must always keep their ears open to new ideas.
I will look at doing a spread sheet in the future with about a dozen popular brands reflecting classes of product.
Without getting into too much detail right now about certain oil suppliers strategy and thinking, Castrol for example who lead the revolution in ester oils 30 years ago for bikes (Mobil led the way in ester oils for aircraft jet engines instead a decade earlier) dont see the need for a heavy weight 2T oil like some other brands to try to dominate the market share. Heavy esters also cost more to manufacture and there is only two suppliers in the world for these. They know that virtually all offroad 2T bikes will be lubricated by the TTS product. They dont bother promoting their heavier viscosity XR-77 product in the same class as Motul 800 or Motrex Racing GP 2T. I dont think they even bring it into Australia.
Oldfart's example there shows that more oil offers cleaner metal surfaces and is a mirror image of my internals (Hospital Standard cleanliness as I described in the past). More oil provides more cleaning action to prevent deposits from sticking to the parts, (the constant incoming additive that contains a % of detergent and scavenging agents keep deposits from forming) but this engine is also an example of good jetting with the type of fuel used.
Why you shouldnt use car engine oils in your 2 stroke transmission or 4 stroke motorcycle.
http://www.maximausa.com/technical/lubenews/winterspring2001.pdf
