Ji, $40 per litre is a very steep price to pay for any oil. I would have thought it would be perhaps $25 at the most...At my local bike shop, Ridersedge, they sell TTS in 4 litre packs for I think $65 and you will get better performance and engine life with this oil than what you are using at the ratios i recommended...........as I have said you do not get what you pay for in your case and all the other Maico riders and VMX owners from using these top end oils. They are wasting their money!
You will experience the better cleanliness and lubricity from the clean burning TTS and their equivalents from other company's. A rule of thumb is dont buy the most expensive oil.
Your piston looks reasonably OK and can be sanded lightly with fine emery paper checked for sizes and reused if OK. One of my pistons had that same burn marks, only much worse, under the eyebrow of exhaust port that was a result of the elongation of the cylinder outwards from overheating and insufficient oil causing this blowby. You may be expereinced these same conditions, perhaps try enriching the jet needle one circlip notch. I could bet that the piston will be cleaner when you pull your top end apart next year with 20-25:1 of TTS and 98 Octane pump fuel. On my piston now there is no brown blowby at all in this region after having a rebore to bring back this "roundness" of the cylinder.
Big Bore bikes are made to shift the gears at roughly 10% above the peak torque curve, if you rev it more than that your rate of acceleration will not increase any more. Your 250 requires you to rev it out a lot longer before changing gears as it is not a 400/440 or 490 so adjust your riding style accordingly.
The oil recomendations in your Maico manual??? The figures of 20:1 would have been written by the wise Maico engineers, the other figures of 100:1 would have been given to Maico by oil companys who waltzed through the door at some point and they guaranteed it would work in their engines. The Maico oil mentioned would have been a rebranded oil with a Maico label made by the same oil company that walked in looking for exposure and sales volume to lower their cost per unit of production.
Lozza is right in saying that high lead content is fuels slow down the burn rate, and we could see this under lab conditions running engine tests with micro camera's in the combustion chambers watching the incoming swirling fuel charge of 4 stroke engines (film slowed down of course for us to see) and the flame fronts were slower as the octane of fuel went higher. In our tests engine we had a device inside the chamber where we could change the size of the chamber at will increasing or decreasing the compression. It was fun to adjust the timing and fiddle with other adjustments to test different formulations and octanes of fuel. Avgas 100 burns slow in low compression motors and some people think that by adding Avgas or racing fuel your bike or car will go faster. But INCREASE the compression ratio and everything comes together to make large HP. But in my experience a 2 stroke just makes more torque and smooth power with higher octane fuels around 100 and 102 race fuels when everything else is constant. Ji saw this too.
For example your normal 91 pump gas in Australia (lowest available here.........I think in the US it is 87) it burns faster than say 95 or 98, and this is a factor in causing detonation if your compression is too high for the fuel.
Also Lead back then allowed a very mild form of EP (Extreme Pressure) additive for a 2 stroke engine (we all know about valve seat wear with ULP fuels in old cast iron non hardened heads) and this did assist with dry film lubrication of sliding surfaces as in cylinders. Now ULP fuel is very "dry" as it contains volatile solvents (like paint thinners) that do not offer any lubrication almost like and LPG engine requiring small amounts of oil injection (Valve Saver).
Also the "Ashless" nature of a 2T oil offers even less residual ingredients for offering a buffer to metal parts. In 4 stroke engines you have residual ash in the form of what is called Sulphated Ash (SA)from the burning of the detergent/dispersant additive package where it was found that a minimum of 1% SA would offer valve recession protection with engines that consumed some oil in their operation that went past the exhaust valve. Diesel engine oil have a higher SA due to higher additve content to combat Sulphuric Acid attack from the sulphur in the fuel.
My point here in mentioning other fuel/engine types is that by using less oil in your premix you are starving your engine (the metal parts that rub against each other) with the essential additives that are contained within them by the formulator to offer a chemical coating to the engine parts (very thin) where you will have chemical to chemical contact rather than pur metal to metal contact.
Castor Oil for instance has the least need for extraneous additional additive treatment due to its tenacious adhesion to metal parts. As Lozza described the term, "Shear Strength" that is a natural quality of this base fluid due to its Polarity. To define this term, Polar Compounds like Castor oil have molecules that have a strong affinity for solid metal surfaces. Sort of like our natural affinity to sexy women and old dirtbikes! These molecules plate out to form a tough friction reducing film that cannot be broken easily through shear forces (eg : cutting forces of the piston rings or port edges). They are also reffered to as having "Metal Wetting" properties to explain it another way. As in any positive quality they are "polar" and at the other end of the spectrum Castor oil absorbs water affecting its storage life and some riders have found rust in their motors from moisture being pulled in via any openings (exhaust and breather). I have seen engines an orange to green corossion all over their flywheels and other ferrous (steel) internal engine parts.
Never heard of "oil drag" in a 2 stroke?...........you learn something new every day.............it is an important aspect that needs to be taken into the equation when spending all that time and money in the workshop to optimise a bikes performance.......Oil hangup is all part of studying fluid dynamics throughout an engine.....Formula 1 teams spend millions in analysing this element..............it robs power through absorbtion almost like a hydraulic brake and is one of the hidden things that most lay people cannot see or predict...........We are all here to learn including myself.
The issues with skidding bearings in my experience (never heard of this happening in a 2 stroke engine and cannot see how as 2T oils do not contain certain additives that promote this) is when people add friction modifiers to their oil charge in a 4 stroke motorcycle application. These are Moly, Teflon, and sulphur/phosphorus brews that are detrimental to not only wet clutches, but to needle bearings where the bearings dont turn and roll over and around the crank pin but their rolling motion is stopped by these "solid" additives as virtually all metal to metal contact is stopped (which in other circumstances is great news) and the stationery bearing then "skids" around the crankpin gradually flat spotting itself. When the oil is then changed and no solid additives are added metal to metal contact (or what is correctly referred to as "Thin Film Lubrication" as in bearing applications.....hence the clearances in bearings to make room for the oil film) returns then you usually end up with a disintegrated bearing and massive engine noise. Sometimes this happens in seconds, with consequences like thrown conrods ending your ride for the day. Many a Harley engine has been lunched when the owner puts in Slick50, Molybond, Nulon or the like and wrecks his needle bearings inside the flywheels on his big end. He thought that since the engine is separate from the gearbox and clutch it is Ok to do this.
Ford had a big issue in the 90's when they put 3% moly greases in their Wheel bearings and had huge warranty work from flat spotting. They went back to the blue tacky grease with no more issues.
My point about oil creating detonation is well known fact that has been around since the engine was designed. When engine oil goes inside the combustion chamber it causes detonation. Ask any car mechanic, any foreign material entering a combustion chamber such as diesel or lube oil will lead to detonation. Maybe I should have used the term "Dieseling" so that readers could understand more what I wrote. Ji perhaps is experiencing this rather than outright full detonation (as defined occurring through incorrect timing, fuel octane, preignition etc) so lozza would be right in saying that if all the other factors are in their correct specifications then detonation should not occur. A heavy molecule of A747 would be harder to convert into a very fine mist when travelling through the carburettor when converted to a gas from a liquid. In Euro 4 diesels nowadays the injection pressure is extremely high (6,000PSI) where the diesel is virtually a gas like LPG and some think one day you could ignite it with a form of spark plug. I believe that in future modern 2T bikes fuel injection will be the norm and if high enough pressures will be adopted then the 2 stroke premix will be atomised to a very fine gaseous form. But I don't think you could fit such a large pressure pump on a motorcycle, but future technology with miniaturisation who knows.
It needs to be noted that our 2 strokes are somewhere between a diesel engine and a normal 4 stroke engine with its fuel. It is why in our old VMXer's cannot really handle Or need) these hi vis oils (that are also the most expensive) that really needs some more education for VMX riders as in forums like this. It is just a case of that we love our bikes so much like our kids so we want to buy them the best (read: expensive) and end up with issues that seem to have plagued many riders in the VMX and also the modern scene. So we are stretching what the fuel systems and engines of our bikes are capable of doing so please use the lighter vis grades of 2T oils for optimum performance.
Ji, I will email that photo of your piston to my tuner for his opinion as well to see if he can interpret anything new. As Lozza said you can interpret the carbon marks on the piston to tell you if your timing is too advanced or retarded amongst other things. My bike detonated like crazy once before I jetted it right (enriched it) but the piston showed no signs of typical detonation after two long rides under these conditions. It did have a ceramic coating but that wouldn't stop the affects of detonation eating it out.
Spanky's article appears here and his revised post is further down the page :
http://www.mxnewsfeed.com/phpbb2/viewtopic.php?t=21Alexander Graham Bells book (out of print) is compulsory reading for anyone interested in getting their 2 strokes running to their optimum. Tuners around the world use his research like a bible. I think I have his book on PDF I will check my files and try to post it on a new post..
I have my old piston I pulled out of the bike that I will post a pic of. I will at some stage pull my cylinder and take a photo of the piston that is currently being used. It is also ceramic and moly coated and this is something I can recommend to owners. I got mine done by Jet Hot Coatings in Castlemaine Victoria who also did the silver coating on my expansion chamber. What do others think about the coating of pistons? has it worked for you? Do 2 stroke tuners such as Lozza adopt this technology for longevity and reliability.
The overall theme and objective of this entire post is to research and offer readers options and ideas to enhance the operation and running of their bikes, and throughout the discussions we can bring up related mechanical concepts (moly coatings to enhance lubrication and ceramic coatings to prevent heat transfer etc) that can further the initial opening discussion of oil ratios/2T oil viscosities. And totatly new posts can be created by people who specialise in these other fields. This will then not lead to diluting the initial posts message and topic of debate.
