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Gregger, you lost me bud. These motors are not different than their ancestors when it comes to air cooled motors. They can run real oil.

I agree that I don't understand why, but I would say, you can simply by changing the oil to a straight 40W.



I agree, you can run any oil in these engines but only on condition.

Oil basics 101 - If you run a synthetic or semi synthetic oil you can follow the normal oil change schedules, even go beyond, but (in a Triumph) if you run regular parafin based multigrade oil, you will need to change it out much more often than Triumph recomends because it won't keep it's viscosity for long. Viscosity is the key to engine life. Now, if you run a mono grade non synthetic such as straight 40W, you won't have any problems so long as you drive in warm weather (reason for multi grade is for cold start ability). A straight 40w would run fine because its viscosity isn't enhanced with modifiers and as such, won't break down. For example, a 4 stroke Detroit diesel runs on 15W40 oil for thousands of hours. It's oil is subject to compression in the bearings and minimual shear. A 2 stroke Detroit diesel needs to run on straight 40W because the multi grade oil would break down causing premature engine wear due to the high shear application (rings moving across the transfer ports in the cylinders chopping the oil, thinning it out, similar to our gears meshing in the transmissions).

Now if I haven't totally confused you we progress to engine type. There is a difference. Some engines include the transmission (like the Triumph) and share a common oil sump and oil. They need an oil that is suited to both extremes, compression in the bearings, and shear in the gears. Synthetics provide this. Other engines have a separate transmission like my former BSA. The transmission was filled with straight 90W gear oil. The engine filled with standard motor oil with no problems.

Hope I haven't totally confused the matter. If so....er...trust me...

Oh yah, forgot to mention, you can mix a standard oil and a typical synthetic (semisynthetic) so flushing the engine isn't required.

12 Rocket Roadster
03 Bonneville America
69 BSA Firebird Scrambler
73 Yamaha TX 750