By: Ron Milam
As you may recall, in last month’s issue I began a series of articles aimed at keeping a trials motorcycle performing like new or hopefully even a little bit better. We explored the effects the exhaust system has on engine performance, and how to clean it. I am sure that each and every one of you rushed to the garage to clean yours. Furthermore, I’m sure that if you did, you are open to suggestions for ways to prevent that nasty build up.
The answer is to spend less money on oil. Trials veterans know that a trials engine requires much less oil than a motocross or roadrace engine. Newcomers however, sometimes have not heard the word. You can tell who they are by following them on the loop and especially up a long hill climb. Clouds of oily smoke belches from their pipes, choking followers and threatening the insect population for miles around.
32:1 is way too much oil. 50:1 is still too much. 80:1 works well. 100:1 is used by many riders, including many factory sponsored riders. 120:1 is used by some people, but I think you are treading in dangerous territory there. There are a few catches though and they are important.
First, you must use a good quality FULL synthetic 2 stroke engine oil. Synthetics have a couple of characteristics that make these high ratios possible. One is that they have an extremely high film strength.
This is one of the most important properties of a 2 stroke oil and a synthetic has a film strength way higher than a petroleum based oil, even with extreme pressure ( EP ) additives. Another characteristic is that they are not partially consumed in the combustion process like a petroleum based oil. Important to the riders of air cooled bikes, is the fact that synthetics are less affected by high engine temperatures. Don’t be fooled by oils that are synthetic blends. What this means is that the manufacturer cheaped out and made a product that you may think is synthetic, but is actually a mixture of synthetic and petroleum base stocks. One example is Maxima Super M. These oils are perfectly adequate for low dilution ratios or in oil injected engines, but should not be used above about 50:1 even on a watercooled bike. Read the label and make sure it says FULL synthetic. If you are not sure ask questions or choose another oil. Some manufacturers such as Belray, have more than one full synthetic. I e-mailed their technical department and found that MC-1 is their best product for high dilution ratios. Check with the oil companies if you have questions.
I am going to break down a little bit here and make a confession. In general, I try to be a cutting edge
kind of guy and go with latest and greatest, etc. Pioneering is great for many situations, but sometimes pioneers get shot in the back by the Indians. Whut da heck is Milam talking about ? This. Factories can afford to experiment. If they get one season from a motor that’s OK. I expect mine to last five or more. That’s why I use what has been proven for years. ELF XT at 80:1. And I am thinking about going to 100:1.If your engine is aircooled, you should not try this. You can talk to some of the guys that ride aircooled bikes, but I think you would be pushing your luck at 80:1. Air cooled engines have greater internal clearances and run hotter than watercooled engines.
Another catch is that you better be danged careful when you mix your fuel. At 100:1 you use 1.44 ounces/gallon. That ain’t much Buddy. The oil that sticks to the side of your measuring cup ( you wouldn’t try this using that little window on the side of your oil bottle I hope ) can be a significant amount. Also, you must be sure to mix it thoroughly before filling your tank. The margin of error becomes smaller at these ratios.
So why take the risk of trying something that is so risky ? It ain’t risky Dude. It’s proven. And here is the good part. Your bike will perform better. Some people think that the oil in a 2 stroke reduces the horsepower output. They think that if you put in less oil , then the engine is getting more gas. No way Hosea. Getting more fuel in is easy. If you want to make more power, put in more air. Savvy tuners, especially road race tuners know that less oil means less power for a 2 stroke. I have seen dyno results at different ratios using the same fuel, oil, and engine. Only the oil ratio was changed. The difference on a 125 road race engine was several horsepower . 16:1 gave the maximum power. It seems that in addition to keeping everything sliding and rolling, 2 stroke oil also helps engine sealing. Although the oil helps the piston rings seal, people often forget that everything is critical in a 2 stroke and there are areas below the rings that need sealing too. This was in a road race engine. In a trials engine the difference will be much less. Did you ever see a trials bike tuned for maximum horsepower? Nope. We value low end power and smooth predictable throttle response. Guys that run a low oil ratios may find that in some situations, oil may pool in their bottom end. Well maybe not in their bottom end , but for sure in their engine’s. They get it the worst when decending a long hill with the throttle off. The oil from the cylinder walls and bearings collects in the crankcase. Since it is not getting blown through with the charge ( no throttle = no charge ), it just builds up there until he reaches that log or ditch at the bottom. He gives the throttle a tug and instead of a blip, he gets a blub. Blips are good. Blubs can get you hurt. What happened? He just fed his spark plug a big slug of oil. It also totally messed up his fuel air ratio momentarily. This also happens to a lesser degree at many parts of a some sections.
So the engine performs better; what else? Your spark plug doesn’t get gobbed up with that afore mentioned evil oily black carbon gunk. In fact, with a cleaner plug you may find that you stall your engine less. Do you ever think about what happens when you stall your engine. You are chugging along at say 350 rpm. Maybe more maybe less. You are on a clean in a classic Charlie Roberts section. ( A classic Charlie section always involves chugging. ) Then the rpms drop to 349 and ooomph. The engine comes uncranked. I know it has to happen at some speed , but is it 349 or 349.5 or even the popular 349.75? One millisecond you’re on a clean and the next millisecond you are hoping for a Merlin Clausing imitation (crank while balanced ). See what a big difference a little thing can make ? One fourth of an rpm seems like nothing, but it just cost our hypothetical rider 5 points. Your performance in an event is the sum total of a thousand small details and situations. You don’t even have to train for this one.
Lastly, and this is where we started; less oil in your fuel means less oil in your pipe. This couldn’t be anything but good.
Many people were kind enough to offer a kind word about my column last month. I truly appreciate the encouragement. Some even offered suggestions for a name. I think I am going to wait until next month to name it and see if there are any kinder suggestions. Next month maybe we will talk about clutches. Or maybe brakes. Or maybe suspension. Eeny meeny miney mo…….
Ron