Maybe I wasn't clear why the spinner oil filter doesn't work as good as a paper filter, and I apologizes for that, I'll try to explain it in a better way.
The principal of a spinning oil filter seems to be simple but isn't when you look at the details.
The idea is that by centrifugal force particles are driven toward the edges of the filter where these particles will accumulate. Once in a while you clean the filter and the process starts over again.
The centrifugal force on the particles is depending on the circular speed of the filter and the weight of the particle and the distance of the particle from the center.
is the centrifugal force
m is the mass of the floating particle
w is the circular speed
r is the radius or distance from particle toward the centre
In this particular case (honda 305) the w (circular speed) is not constant, it changes linear with the rpm, it's influence in the formula (thus on the particle) changes with the square of that.
The first experiences with full synthetic oil (5W20) I had were with Honda SS50 / CD50 engine.
I experienced that, when I used the oil, the engine was cleaned within a few hundred miles, and everything what was lying around in the cases would accumulate in the spinning filter (part of the clutch). So, in this case the spinning filter is working fine.
Later I experimented with full synthetic oil on larger engines (CB72) and found the same results.
The first conclusion was that the spinning filter works fine with full synthetic oil, so I started using this oil in a rebuild engine (and a new oil pump). Every 1000 km I cleaned the spinning oil filter and every 4000 km I changed the oil. After 12.000 km I was curious how the internals of the engine would look like, so I decided to open it up. Everything was in as new condition and measurements after 12.000 km where comparable with the initial values before installation.
So nothing wrong here ? Yes and no. I also inspected the oil pump and I found wear at the oil pump gears (as stated it was new 12.000 km ago). I checked with the oil pumps used in the
small displacement engines and there was no sign of wear. Time for looking for differences.
It took a while, but in the end I found the few reasons for the wear on the oil pump in the CB72 engine. The mean reason is the difference in construction between the oil filters, and I will explain with the formula above.
When I compared the values in this formula for the two engines I found a few differences.
Mass off the floating particles in both engines are (assumed) the same.
The radius of the area where the particle is (toward the centre) in the centrifugal filter is depending of the radius of the filter itself, and here I found a difference in construction. The radius of the small displacement engine is a little bigger then in a CB72, so the force on the particle is higher.
The circular speed (w) is depending on how fast the filter is turning around, and here I found the also construction differences. In the small displacement engine the oil filter is attached to the clutch (part of the clutch) and this clutch is directly attached to the crank. Therefore the speed of the filter is the same as the crank speed. In the CB72 it’s not directly attached to the crank but the power is transmitted by a chain. The chain gears on the crank and oil filter would be the same there isn’t any difference, but this is not the case. The filter runs with a higher speed then the crank, not much, just a little (24/22 teeth).
The difference in driving styles are also responsible for a difference in speed of the filter.
Since the crank speed is depending on the rpm, the rpm of the engine dictates the force (Fc) on the floating particle. I ride the small displacement engines with much higher revs as the CB72 engine, because of the lack on power at certain speeds. Where I tend to run my CD50 at a constant speed of 55 km/hour the engine is running over 7500 rpm. I calculated with an average of 7000 rpm. At the CB72 I’m not running this rpm as often as I do on the CD50. I calculated with an average rpm of 4500 for the CB72.
So, when we look at the impact on the force on the particle, with the data above :
Fc for the CB72 compared to the Fc for the CD50 :
Mass of particles is the same, so mcb72
Radius of the CB72 is 0.8 of the CD50, so rcb72
= 0.8 rcd50
Circular speed of the CB72 is 0.64 of the speed of the CD50, so 0.64 wcb72
The construction factor between CB72 and CD50 is (24/22), so 1.09 wcb72
When filled in :
*r and Fccb72
*r and Fccb72
= 0.43 m*w2
This means that the centrifugal force on a floating particle in the CB72 is a halve of the centrifugal force on the same particle in the filter of the CD50
A full synthetic oil is a very powerful detergent, it will clean the engine very good and drop the particles in the filter due to the above explained principal. The very small particles (like cool) are not filtered out by the filter, but don’t do any harm to the engine either.
But if the detergent power of the oil exceeds the influence of the Fc on the particles in the filter, these particles will not be held in the filter and start floating around in the oil.
This means that when the running speed of the engine is low (rpm) the oil starts cleaning the filter itself, and this is probably why I found wear to the oil pump gears. In the breaking-in process I never push the machine to it’s red line, so dirt collected in the filter was washed out and went through the pump.
The conclusion of the oil analyse was that there where a lot of particles floating around in the oil, which should be filtered out.
After this "discovery” I drained the oil more often, found less particles in the drained oil, and the oil pump stayed within specs.
This is the reason why I developed an oil pump with a paper filter, sometimes I like to ride low rpm’s (as a tourer) without the knowledge of ruining my oil pump, and I don’t want to change the oil every 1000 km or so.
I analysed the oil and after 2000 km, the oil is still good enough to use.
Like I stated earlier, with this oil filter solution I can use all the benefits of a full synthetic oil without the problems it causes at low revs.
So before you put a half synthetic / full synthetic oil into you engine, make sure that your oil filter is clean. If there's any sludge in your engine cases it will be (partly) washed out by the new oil and dropped into the spinner oil filter. Needless to say you have to check the oil filter within a very short period after using the new oil, depending on how clean the internals are.
I hope this explains a little more about the choices I made.