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Kurt in NJ · 04-21-2012, 10:14 AM

I see much obsession with the "need" to have a "full flow" filter, but not much about the facts of filtering, with the internet it is much easier to do the research, and from taking apart many engines and filters I know that just beacuse the oil is going through the filter it doesn't mean that it is being filtered.( the internal componets of many filters are pretty cheap, one I took apart was a coffee filter draped over a recycled can with holes--I was curious because it rattled, it didn't have a brand name)

From SAE papers---"Particles under 20 microns are most harmful to rings and bearings" ---it seems reasonable, the particle has to be smaller than the clearance of the bearing to get there (25 microns is about .001)

Full flow filters are not that good at less than 20 micron debris ---they can't be,you are trying to get all the oil through fast ----85% capture rate in a single pass
From filter testing--
40% capture at 10 microns
60% at 20 microns
93% at 30 microns
97% at 40 microns

If you use thick oil on startup most of the oil goes through the filter bypass---it is too thick to go through the filter.

A bypass filter has a much better capture rate
98.7% at 2 microns
39% at LESS than 1 micron
usually filtering 5qt in 10 min

The ideal filtering system has both a full flow filter for large stuff, and a bypass for small stuff, the Mercedes that has a million miles did it with a screen for full flow, and a bypass filter to do the filtering ---I have reused bearings with over 200,000 miles on them in these engines

Most of the debris in a rebuilt engine are from the rebuilding process that wern't cleaned out during assembly.

For most of us a properly rebult engine with clean assembly will outlast your ownership---without a filter, with the original bypass filter it will probably be the next 3 owners ---I would worry more about having proper mixture to prevent washing down the cylinders with gas and diluting the oil, and having thermostats to have a quicker warmup to get the oil to temperature to boil off condensation to prevent acid formation.

04-21-2012, 10:14 AM	#10
Kurt in NJ Senior Member Join Date: May 2010 Location: on the Littlefield Posts: 6,159	Re: oil filter for flathead I see much obsession with the "need" to have a "full flow" filter, but not much about the facts of filtering, with the internet it is much easier to do the research, and from taking apart many engines and filters I know that just beacuse the oil is going through the filter it doesn't mean that it is being filtered.( the internal componets of many filters are pretty cheap, one I took apart was a coffee filter draped over a recycled can with holes--I was curious because it rattled, it didn't have a brand name) From SAE papers---"Particles under 20 microns are most harmful to rings and bearings" ---it seems reasonable, the particle has to be smaller than the clearance of the bearing to get there (25 microns is about .001) Full flow filters are not that good at less than 20 micron debris ---they can't be,you are trying to get all the oil through fast ----85% capture rate in a single pass From filter testing-- 40% capture at 10 microns 60% at 20 microns 93% at 30 microns 97% at 40 microns If you use thick oil on startup most of the oil goes through the filter bypass---it is too thick to go through the filter. A bypass filter has a much better capture rate 98.7% at 2 microns 39% at LESS than 1 micron usually filtering 5qt in 10 min The ideal filtering system has both a full flow filter for large stuff, and a bypass for small stuff, the Mercedes that has a million miles did it with a screen for full flow, and a bypass filter to do the filtering ---I have reused bearings with over 200,000 miles on them in these engines Most of the debris in a rebuilt engine are from the rebuilding process that wern't cleaned out during assembly. For most of us a properly rebult engine with clean assembly will outlast your ownership---without a filter, with the original bypass filter it will probably be the next 3 owners ---I would worry more about having proper mixture to prevent washing down the cylinders with gas and diluting the oil, and having thermostats to have a quicker warmup to get the oil to temperature to boil off condensation to prevent acid formation.