If the filter hangs vertically below the adapter, then there is probably
no need for an anti-drainback valve. Note the "probably". Filter
position isn't the only deciding factor here. On some engines, the
position of the filter relative to the oil galleries can cause oil to be
siphoned out of the filter even if it hangs vertically. I don't know the
BMC engine used in the MGA well enough to say if that's an issue in your
case. Generally speaking, though, and anti-drainback valve is necessary
only if the filter is off-vertical.
I didn't say that a pressure relief valve is necessary in this
application. I said only that some seemingly identical filters have filter
bypass valves, others do not. The filter heads used on our cannister
filtered BritCars already have filter bypass valves built in, so none is
needed in the filter itself unless the one in the filter head is removed
when the adapter is installed.
For your MGA application, it sounds like a plain filter (no anti-drainback
valve, no bypass valve) will do. On my TR4, where the filter body mounts
horizontally, I need an anti-drainback valve but no bypass valve.
You won't find these things specified on the filter box. Instead, you'll
need to find the manufacturer's specification book. Somewhere around here
(can't find it at the moment) I have a huge thick old book from Fram that
provides detailed specs for all of their filters (well, all of their
filters as of about 1975 - it's an old book). You can cross-reference
filters by body size, thread size & pitch, relief valve (yes/no),
anti-drainback valve (yes/no), and other useful features.
If your friendly local filter dealer doesn't have a detailed specs book
(he probably won't), you may be able to get one from the local wholesale
distributor or directly from Fram, AC, Purolator, or whoever. If worse
comes to worse, contact the manufacturer's customer service or tech
service department. Tell them the thread size & pitch, the gasket
diameter, and the approximate body size, and indicate whether or not you
need an anti-drainback and/or bypass valve. They should be able to give
you the appropriate filter number.
In your case, where the filter is vertical and the filter head probably
still has its original bypass valve, which filter you use probably isn't
critical as long as it fits. Having an anti-drainback valve when it isn't
necessary won't hurt anything. Having a bypass valve when you don't need
one is probably okay, but watch the behavior of your oil pressure gauge to
make sure. I once put a filter with a bypass valve on my TR4 and saw some
really odd gauge readings before I realized the bypass valve in the filter
was the cause. The pressure would rise to a certain point with engine
revs, then drop back suddenly about 10 psi, apparently when the bypass
valve in the filter opened up.
Now, even with that 10 psi drop the pressure was more than adequate, but
what bothered me was that this meant the oil was no loger getting full
filtration. The filter bypass valve, whether in the filter head or in the
filter itself, is designed to allow unfiltered oil to get to the oil
galleries in the event that the filter clogs up. In my case, however, the
bypass valve in the filter opened up at pressures that are normal for a TR
four banger. Not good!
On Mon, 14 Apr 1997 dmeadow@juno.com wrote:
> So we come full circle on the original question as to which is the proper
> replacement filter for the spin-off conversion kit for the MGA. Using
> only Fram numbers for simplicity, we have the following candidates:
>
> PH 3600
> PH 43
> PH 3614
>
> I looked at all of these over the weekend, since I have this same problem
> that I solved unscientifically by using the one that *looked* like the
> one that came with the kit (which is the PH 3614). How do we know which
> is right? The PH 43 says it is for MG's, but I'm sure that refers to MGB
> applications. In the MGA the filter hangs "properly" so anti-drainback
> wouldn't seem to be an issue. An internal pressure relief valve is
> required? Why? Surely the cotton filter / canister stock setup has no
> pressure relief valve. If it is required, how does one know the proper
> pressure, then how do you know if your filter has it? I looked at the
> boxes and found no specifications, beyond recommended applications.
>
> As often happens, the more answers we get the more muddied the subject.
> What is the definitive answer? Where did the recommendations come from
> (Barney, I recall the PH 43 was yours)? Science, or (as in my case)
> ignorance?
-----------------------------------------------------------------------
Chip Old 1948 M.G. TC TC6710 NEMGTR #2271
Cub Hill, Maryland 1962 Triumph TR4 CT3154LO (daily driver)
fold@mail.bcpl.lib.md.us
If cars had evolved as fast as computers have, by now they'd cost a
quarter, run for a year on a half-gallon of gas, and explode once a day.
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