On Mon, 14 Apr 1997 20:11:57 EDT dmeadow@juno.com writes:
>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
>
< ..... 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.
>
> ..... Where did the recommendations come from (Barney, I recall the PH
43 was yours)? .....
I keep things, so surprisingly, I can answer all those questions, I hope
you like the answers. Remember that MGA and MGB engines are very
similar, and the oil filter heads are interchangeable.
I bought a spin-on adapter for my MGA from Moss (actually two) several
years ago. The first was a simple hanging unit (March '88), Moss number
235-940 similar (but not identical) to the current Moss 235-940. That
one had a design defect, didn't seal correctly internally to the engine
block, and would bypass oil without being filtered. Moss discovered the
problem and stopped selling it shortly thereafter. The specified filter
at that time was Moss 235-950. External shape of a filter can change
over time without affecting internal function. I believe at that time
the 235-950 filter was longer and more slender, similar to the shape of
the original canister on my MGA, don't know what shape it is today.
I returned the defective adapter for exchange in January '89. The only
other spin-on adapter they had available at the time was the 460-910
inverted unit, so I rather begrudgingly accepted it. Over the years I
have come to appreciate one advantage of this design. It allows me to
remove the engine from the car without removing the filter from the
engine (which I have had occasion to do). It does however get in the way
of checking the dip stick, generator wires, and distributor. The filter
specified for the inverted unit is 235-960, and I think the difference is
the anti-drainback check valve (not sure) and definitely an internal
pressure relief valve. Not taking any chances at the time, I kept the
box top from the filter for reference, and I still have it. It was a
Cooper filter Z27A, still has the 235-960 number stuck on it.
For a couple of years I carried this Cooper number with me whenever I
went looking for a new filter. It cross references to Fram PH43 and NAPA
1068, still good numbers today. The inside box flap on a NAPA filter box
gave me the rest of the numbers, AC Delco PF-20, Motorcraft FL-300,
Purolator L20081, WIX 51068. All of these filters have the rubber check
valve that you can see by looking through the oil supply holes in the
open end of the filter. The purpose of that check valve is to prevent
drainback so you get quick oil pressure on startup.
Now I just went and did some real digging through the old steamer trunk.
The original MGA oil filter setup DOES have a pressure relief valve built
into the filter mounting head (the part where the external pipe
connects). None of the spin-on adapters have a relief valve in them, so
I suspect this is why Moss specifies a spin-on filter with a relief
valve.
And now for some opinionated stuff.
Point 1: These days I personally believe that an internal pressure
relief valve is not necessary, should be normally non-functional if you
have one, and may even be detrimental in certain nasty circumstances.
Under those conditions where the internal relief valve does do something,
you have some big problems to think about. I don't personally care if an
oil filter has an internal relief valve, makes no difference to me. The
purpose of the internal relief valve is to allow oil to bypass the filter
under conditions of high pressure drop across the filter to prevent the
collapse of the filter element. This high pressure differential across
the filter can come only from excessive flow or a clogged filter. Either
of these conditions is a very bad condition in itself, and I intend
(hope) to forever avoid them.
HOWEVER, many years ago when I used the original cotton/felt filter
elements and really cheap (recycled) nondetergent engine oil, the filter
would look particularly well gummed up with only 2000 miles between oil
and filter changes. Maybe the factory had a good idea with the relief
valve in the filter head in those days. The newer detergent oils are
much, MUCH better in that respect. I've never had a dirty engine or
dirty filter using modern oils.
If you have a stuck closed pressure relief valve in the engine block you
get continuing higher pressure with higher engine speeds as flow
increases. Without a relief bypass, pressure increases dramatically with
engine speed, and if the engine is in otherwise good condition it can
burst the filter canister. The filter internal relief valve has nothing
to do with this, likely still having low pressure differential across the
filter element.
If the engine is old and worn, having large clearances in the bearings of
the crankshaft, camshaft and/or rocker shaft, you can get substantially
higher flow, possibly enough to upset the filter internal relief. At
this point the filter is not filtering all of the oil, which is possibly
detrimental. An indication of an old loose engine is low oil pressure at
idle, not coming to full pressure until high RPMs. If you have one of
these, yourengine needs work anyway, so don't blame the oil filter.
If you neglect to do oil changes for a long time, the oil can get dirty
enough to clog the oil filter. Then you get a big pressure drop across
the oil filter element, the filter internal relief will bypass some
(possibly all) of the oil, and the oil will not be properly filtered,
also very detrimental, as well as the dirty oil. This condition will not
give any indication on your pressure gauge because the dump pressure for
the filter internal relief valve is way below the normal engine oil
relief pressure, like maybe 5 PSI. If your oil is not being filtered
because of a clogged filter, don't blame the filter.
Since I have no intention of driving my car with a stuck oil pressure
relief valve, a clogged filter, or loose bearings, a pressure relief
valve inside the oil filter is of no concern to me, be it there or not
there.
Point 2: Gravity is ever persistent, so oil drainback can be a
problem even with a hanging style filter. With a hanging style oil
filter the filter itself will stay full of oil, but the rest of the oil
can still drain down to the point of leaving the system full of air and
maybe even the oil pump without prime. I believe that the hanging filter
setup can also benefit from a filter with a check valve for
anti-drainback. This should keep the oil from draining out of the system
between the pump and the filter so the pump can't loose its prime. The
system is sealed between the pump and filter, so no way for air to get
in, so the oil will stay in there if you have the check valve in the
filter. One possible exception to this would be if your block mounted
pressure relief valve sticks open or leaks allowing back flow and
introducing air during engine off time.
With an inverted filter there is another way for gravity to pirate your
oil, even with a properly working check valve in the filter. The oil
circuit after the filter is not sealed, all of the bearings being open to
air on the discharge side. With long periods of engine off, oil can
dribble out of the bearings, and air can get in. Eventually the air can
bubble its way through the system and fill up the inverted filter as the
oil gradually drains out. While the oil pump may not loose its prime,
you can still get a few seconds of zero pressure on startup. But, there
is also a help for this problem.
Look in the Moss MGB parts catalog, check out the picture of the inverted
spin-on oil filter adapter. You will see on the filter end of this
adapter a tube which extends upward into the center of the filter. This
tube prevents oil below the top of the tube from draining into the engine
block during engine off periods, maintaining oil level in the filter as
high as the top of the tube. The length of the tube is sized to
accommodate a fairly short filter (and here's the hook). A taller filter
will slightly improve oil cooling capacity, but can also contain a
substantial air bubble after extended engine off periods. In this case
the shorter filter would be better, allowing for only a small air bubble
in the worst conditions and quicker pressure buildup an startup. So, for
the inverted filter installation I would opt for a short fat filter and
avoid the taller "Ford" filter.
Point 3: You may all have some fun and flame me on this one. I
believe that NAPA oil filters are of good quality (I just trust the
company and its reputation). Other than that I would definitely try to
stick with a major brand name of filter (for the same reason). I've seen
a lot of comments on the list recently flaming FRAM filters for faulty
check valves, but I haven't used one in years so I have no personal
opinion there. I would think it makes sense that they would fix the
problem, but I ain't assuming anything, and it's a risk I don't have to
take. Other than that, if you get a major brand filter that physically
fits on the spin-on adapter and does have the visible rubber check valve,
I think you'll be OK. Any size or shape should work.
Did anyone finish reading this whole post?
Barney Gaylord
1958 MGA
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