Some opinions by various contributors to the Yahoo BSA Group on whether the use of oil filters is wise
You be the judge !
| Well, I can't resist
it any longer - though I promised myself I'd keep out of it!!! It seems
to me all of this filtration thing is losing sight of the purpose of
using a filter in the first place. Trunk piston engines (those who's
pistons are directly connected to the connecting rods) will, by fault of
design, allow products of combustion to enter the crankcase. Products of
combustion include (but are not limited to) carbon, water, sulphurous
and or sulphuric acid. The acids are considerably less in petrol engines
than in diesel engines which is why some oils are sold as being for
diesels (they contain an alkaline additive to neutralise the effects of
acids) and these oils should not be used in petrol engines. OK, I
digress slightly. Other contaminants include metallic particles
from bearings and so on. the purpose of fitting a filter is remove
the large particles (we're not talking large as in mesh size in the
sump, but at multi-micron level) so that the plain bearings i.e. shell
big ends and timing side bush bearings do not become damaged by
erosion or impingement of the particulates in the oil. Bearing
clearances are designed in the region of 0.76thou to 2.64 thou over a
range of modern bikes, with the modern sports bikes being at the larger
clearance end - quoted by manufacturers as ~ 0.019mm up to ~ 0.066mm
over a range of bikes and were probably designed in the region of about
1.5 thou in our old BSA's.
Shell bearings are designed to float on a film of oil and the bearing material (generally white metal) should never be in direct contact with the crankpin - it uses the hydrodynamic pressure of the oil to keep them apart. Now, bearings wear at start up when there is no or very little oil pressure - the first turns of the engine before it fires and develops oil pressure will cause the bearing to scuff on the crankpin. Once the engine is running, the main concern is to supply an adequate amount of lube oil to the bearings. The oil should be clean and this is the importance of the oil filter. But, before that, it should be understood that our BSA's (with the exception of at least the Rocket Three - I don't claim to be an expert on all the models and developments) were designed without filters at a time when cars were fitted with filters. To overcome the shortcomings in design, BSA sought to include their own filter. Namely, the sludge trap. This is basically a centrifugal separator and works by flinging the heavier solids towards the wall of the trap whilst allowing the lighter liquid phase (lube oil) to pass through to the bearings. Because the lube oil recommended for use in those days did not include the modern additives such as detergents, the system worked well. The main drawback is that periodically, the sludge trap needs to be removed and cleaned. This means a full engine strip. Having said that, you will recall that I mentioned that the bearings do contact the crankpins on start up when the oil pressure is non-existent or at best reduced. So, it will become apparent that the bearings need to be renewed at intervals, which is an engine strip - hence cleaning the sludge trap is no big deal at that time. During oil changes when running on straight run (non-additive) oil, it is also important to clean out the oil tank, as sediment will collect in the bottom of the tank. This build up will be considerably less or non-existent when using detergent oils. The main point of the filtration thread as I see it, is that filters NEED to be used if you decide to run your engine on a modern, additive packed oil. the detergent additives prevent the sludge trap from doing its job because the particulates are held in suspension in the oil and the only way to remove them is by fitting an oil filter - or, of course, very regular oil changes! Therefore, whilst agreeing in principle that the chosen filter should be designed for the job, it is highly unlikely that fitting the wrong oil filter can wreck an engine. At worst, it will not offer the degree of protection needed but I cannot see how that can be any worse than not fitting a filter when one is needed by virtue of the lube oil chosen to do the job. Choice of lube oils is an entirely different thread and has been done to death here in the past. Suffice to say it is a matter of choice in what one believe to be the right thing to do. Oil filters are more coarse than fuel filters because of the finer tolerances designed into fuel injection and other component parts employed in fuel systems. Take it or leave it, but my only intention is to inform as best I can such that the uninformed might be slightly better informed and better placed to make a decision - or, to inspire more questions to be asked!! |
| The main point of the filtration thread as I see it, is that filters NEED to be used if you decide to run your engine on a modern, additive packed oil. the detergent additives prevent the sludge trap from doing its job because the particles are held in suspension in the oil and the only way to remove them is by fitting an oil filter - or, of course, very regular oil > changes |
| The bypass valve setting is the
maximum resistance (or backpressure) that the filter will create. This
can occur when: (a) The filter is partially blocked but the oil is very thick because the engine is cold (a temporary situation) (b) The filter is partially blocked but the oil pump flow rate is high (high rpm) (c) The filter is totally blocked (the bypass valve is open at idle rpm and with hot oil; there is maximum differential pressure across the media). Although the micron rating of the media is important (all thing being equal a finer media is more restrictive), the maximum pressure created by any of the media choices that the filter manufacturer offers remains the same; the bypass valve setting. Ie: 5, 10 20 or 40 micron cartridges would all create a maximum back pressure of 12 psi. Its my view (and experience) that a back pressure of even 20 psi created by a return line filter will not pose any problems to an oil pump in satisfactory condition. Don't forget that the other (delivery) section of the pump will easily reach the relief valve setting of approx 60 psi while the oil is cold, and the bottom end's internal clearances are minimal (cold). The scavenge section is manufactured to the same tolerances. A comment on filter ratings. Many (most) automotive filter manufacturers use "nominal" filter ratings which means that their actual particule removal performance can vary enormously from manufacturer to manufacturer. This is because they could have used differing test procedures (usually the case), and therefore are not comparable. If however they can quote an Absolute rating, then their results are credible because they have used the recognised ISO testing procedure. A 20 micron filter nominal rated would have an Absolute rating varying from 30 to 80 micron, depending apon who the manufacturer was. Ask your expert for more detail about the rating of the element he is recommending. Is it a nominal or Absolute rating? What is the Beta ratio (particle removal efficiency rating) of the media at the micron rating he claims it to be? When you halve element surface area, element life reduces by around 3 times (rule of thumb), all other factors being equal. This is the major disadvantage of using a smaller filter (go as big as possible / practical). Also, it is dangerous to claim a specific life time for the element, as it will vary depending apon the oil temp (length of your rides), oil flow (speed of rides) and rate of contaminant ingression (engine wear). If there is no indicator fitted to the filter (ie pressure gauge), how do you know when the bypass valve is open? I suggest visually checking the oil condition before the scheduled element changeout time, and if it appears dirty (metal particles, etc) then change the oil (and investigate/worry!). |