Jack W. Drews wrote:
> Does anyone have personal experience with blocking or altering the
> bypass valve on the filter head of TR's?
>
> The stock oil filter head on a TR is made with two relief valves. One
> regulates pressure to the engine by dumping oil back to the sump so
> the pressure to the engine isn't too high. The other one is what I am
> interested in.
>
> The second one is a bypass that senses pressure differential between
> the oil filter inlet and outlet oil pressures, to prevent a clogged
> filter from starving the engine. It also prevents starvation when the
> oil is too cold and doesn't want to flow well through the filter. The
> problem with that valve is that it lets oil bypass the filter at too
> low a pressure. The big disadvantage for race engines is that when
> something starts to disintegrate, all the debris bypasses the filter
> and contaminates the whole system -- particularly damaging the
> expensive crank and the less expensive oil cooler and hoses.
>
> I'm thinking that in a race engine, we change oil often and the
> likelihood of a clogged filter is slim. Likewise, most of us use
> 20W50 or some such, which acts like 20W at low temperatures.
>
> Here's my question: It seems that for our race engines, we could
> disable the bypass valve, or at least significantly change the
> pressure at which it bypasses, to make the oil filter more of a full
> flow filter than a bypass filter. Has anyone done this? Pros and cons?
>
On the better heavy-duty commercial systems, bypass oil is shunted to a
second filter when the differential reaches the preset, and turns on a
monitor light to indicate to the operator that the primary filter needs
attention. That's probably the ideal situation, but a bit impractical
for an occasionally-run vintage racer.
I suppose the question would be how much differential would prevent the
sort of problem Jack describes. Too much differential and the filter
can load up with gradually-shed pieces which then tear through the
filter media and into the system--no advantage there--along with a
reduction in oil pressure at precisely when more pressure is needed to
keep the engine alive. Too little and the engine is awash in unfiltered
oil. As I recall, the commercial units described above have a factory
preset of, depending on the system manufacturer, about 8-11 psi,
although I've heard that a differential of as little as five psi
indicates a fairly loaded filter (systems for heavy-duty auto
transmissions, which run at pretty high pressures and volumes, seem to
be preset for about 15 psi differential).
What is just as important, I would guess, is knowing when the filter is
bypassing. A switch grounding a light would give some indication, but
for some serious testing, one might need to install some pressure taps
to separate gauges to show the differential.
Cheers.
--
Michael Porter
Roswell, NM
Never let anyone drive you crazy when you know it's within walking distance....
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