* Finally please remember that all of the above information is provided on the strict
proviso that any modifications or changes not carried out specifically by Classictrial,
are not guaranteed or warranteed in any way, and are entirely the responsibility
of the individual carrying them out, and that Classictrial are not responsible in
any circumstances for damage or injury that may occur as a result of poor workmanship
The lubrication requirements of a 2T trials bike are quite different to those of much more highly strung road race and MX machines! There appears to be a good deal of confusion related to this subject, as well as the selection of appropriate oils and correct fuel-oil mixing ratios, so hopefully this page will make things a little more clear, and reduce the amount of widespread myth-information relating to 2T lubrication for Trials!
In regard to older machinery manufactured when the relatively basic 2T oils then available effectively dictated rather oily fuel-oil mixtures, riders need to be aware of the fact that modern synthetic oils are a great deal more effective than those used in the 70's and 80's. In real terms this means that a modern fully synthetic oil mixed at 80:1 will provide far better lubrication performance and engine protection than old style oils mixed at 40:1!
In testing modern synthetic oils have been run at ratios of up to 160:1, with no problems, which is a measure of just how very effective they are! On all 2T motors a relatively large proportion of the intake charge of fuel/air finds it way out of the exhaust port, not having been burned in the combustion process. This is the main reason selection of an appropriate fuel/oil ratio is important, as very oily unburnt fuel tends to clog things up much faster than fuel with less oil added.
Essentially low heat/rpm Trials motors do not run hot enough to need the old style fuel-oil mixing ratios, when modern synthetic oils are being used. Using overly large amounts of oil is not likely to cause damage, but will slow the combustion process, reduce EGT (exhaust gas temperature), and clog absorption type exhausts much more quickly. The main reason road race and MX bikes require more oil, is to help with dissipating the far higher levels of heat generated by these motors.
The main effect of using overly large amounts of oil for Trials is that motors will be noticeably less responsive than those running on a more appropriate fuel/oil mix ratio. This lack of responsiveness will become more evident over a period of time as exhaust ducts become clogged with carbon and residues of oil not burnt in the combustion process. If you choose to use old style fuel-oil ratios, then its best to use a mineral or semi-synthetic oil, as these will burn more readily than fully synthetic lubricants, and this will reduce the effects of clogging.
In terms of mix ratios using fully synthetic oils, 80:1 is fine for modern water-cooled trials machines, and taking into account the slightly higher running temperatures of air cooled motors 70:1 for these bikes. However for Trials applications we would strongly recommend the use of a fully synthetic race type 2T oil such as Castrol XR77, which is specifically designed for competition use. We would advise seeking advice from oil producers on mix ratios, if you chose to use low smoke road type lubricants, some of which are of very low viscosity due to the amount of kerosene added.
Use of 2T lubricants containing vegetable oils is not advisable for Trials machines, as while castor based vegetable products perform very well in high rpm/heat race engines, they are simply not required for Trials machines. Use of such oils can lead to problems with gumming up internal parts, fuel oil separation, as well as not providing the type of corrosion protection afforded by a good synthetic lubricant. Oils made using synthetic base with a small proportion of vegetable oil (such as Castrol 747) are more appropriate, but are better suited for use with leaded race fuels.
A common fallacy relating to 2T lubrication is that machines with “steel” cylinder liners, require far more oil than those with Nikasil type cylinders. In point of fact the material a cylinder is made from has nothing to do with the amount or the type of oil required. However if a cylinder has been poorly finished, bore clearance is not correct, or low quality pattern pistons are being used, then using excessive amounts of oil may possibly help to prevent engine damage.
Finally in regard to the use of current alcohol enhanced unleaded fuels, it is very difficult to get any real idea of how a motor is running by recourse to checking the spark plug colour. This means that it's only too easy to have problems when attempting to set up carburetion (especially the main jet size). Working in conjunction with Honda HRC, Castrol have managed to overcome these difficulties through the introduction of XR77, which is specially formulated to work with modern unleaded fuels, and will also provide accurate plug colour readings.
Many thanks to the technical departments of Fuchs/Silkolene, Ammsoil, and Castrol for help with accurate information concerning 2T lubricants, and specific end use applications.