MG-Cars.net

Welcome to our resource for MG Car Information.

Recommendations

Parts

MG parts spares and accessories are available for MG T Series (TA, MG TB, MG TC, MG TD, MG TF), Magnette, MGA, Twin cam, MGB, MGBGT, MGC, MGC GT, MG Midget, Sprite and other MG models from British car spares company LBCarCo.

MG MGB Technical - IMPORTANT! Filtering oil, air, and morons

This might save an engine, so listen up!
I have been puzzled by repeated mention of oil pressure drops related to filter changes, and now have come across one possible cause. A long distance customer (79 MGB) called to say that he had taken his car to have the oil & filter changed, and on driving away had 10psi, instead of its normal 60, so he went back, gingerly. They admitted that they had put a modern 5W-20 or somesuch in, rather than the 20W-50 requested. They changed the oil and said it was now OK, so he drove off, NOT looking at the gauge, since it was "OK". Fortunately he was in the city and driving gently, because when he did look at it, it still had 10psi.
He called me, and then sent it the 100 miles up here via AAA.
The very small filter was a dead giveaway, since it was about the same height as the length of the standpipe. On examination, the standpipe had been in contact with an internal support in the filter, in fact bending it. The standpipe was effectively 98% blocked; if he had made one heavy acceleration run, he would most certainly have scattered the engine. Other filters may have similar but less drastic effects if the standpipe is a bit less restricted than this one was. A difference of 1/8" in the internal construction could give normal performance at low speed and total disaster at full throttle. I would recommend that any filter be examined to be certain that all internal components are at a minimum a full diameter away from the standpipe when fully tightened. I have noted that many parts listings list things like "MG, all, 71-80". This filter screws on to an A-series and may in fact be correct for that app, but it certainly isn't for a B. Be really careful if you let anyone but yourself change filters.

I have long hated standpipes that could reasonably be expected to allow the possibility of total blockage under abnormal conditions, and have taken to cutting notches in the end of them so that even in a case like this it is impossible to block them completely. The same thing applies to oil and fuel pickup pipes, as in Magnette, where if the sump gets mashed it can block the pickup.

As if that's not enough, this same car has a pair of the wretched but flashy "Stellings & Hellings" air filters fitted. I've been telling him for a long time that they must go, and I am tired of having to clean the carbs every time I see the car, which usually has less than 2000 miles between visits. So I measured them,and these are the results, formerly posted on the Spridget board:

Air filters
Crappy "Stellings & Hellings" filters for HS4 SU. May not be real S&H, but the design is so bad as to make this irrelevant.
These are the chrome ones with perforated chrome sleeves on both sides of the foam element.
Airflow area available:
84 holes @ .190dia. = 84 x .095sq x 3.14 = 2.38 in sq per filter.
That is maximum at the inner sleeve, reduced by alignment of the similar outer sleeve and foam.

Airflow area of OE paper, gross:
3 3/4 D X 2 deep x .8 estimated screen coefficient = 33 in sq per filter.
Actual element is unfolded size = .550pleat width x 2sides per pleat x 3depth x 76 pleats = 250.8 in sq.
Note that ONE pleat has nearly 50% more filtering area = 3.3 in sq. than the entire S&H filter!
The S&H has about 7% of the gross and 1% of the element area available in the OE unit.
This means that not only is it very restrictive, but also that air velocity in the media is so high as to make any useful filtration impossible.
S&H also has an bad backplate, further restricting air flow, and it is so flimsy as to not retain the gasket, which shrinks into the intake, making it worse still. The car I am working on has about a 1 1/4 hole through the shrunken gasket, which is the correct 1 1/2 original type.
FRM
FR Millmore

The oil filter thing is really scary. I recently pulled a Fram filter and replaced it with a NAPA Gold 1068. My oil pressure went up by 10 lbs. Zowie.

R.
Rick Stevens

Fletcher, Thanks for the post. I recently purchased a WalMart Super Tech ST16 oil filter. It is listed in their catalog as the correct filter for an MGB. I didn't buy it to install in my car, I wanted to cut it open and see what was inside. The filter is short, the inside depth is approximately 2 inches. The box has a statement that it traps up to 2X more dirt than leading national brand. The filter element has paper end caps and a lousy combination anti drain-back and by pass valve. I cannot tell who makes it but it's made in the USA and looks like is was made by Champion, they make lots of store branded filters. I would not use the WalMart oil filter in my cars.

Clifton
Clifton Gordon

Clifton-
This one is PowerFlo SL10241. It is exactly two inches from the thread boss to the internal support piece, after it "clearanced" itself. So you got one too, ain't cha lucky!
FRM
FR Millmore

The oil filter for late 70's & 80's chrysler v8 engines is plenty large, is readily available, fits right and works great.
They are commonly available in quality ranging from cheap to premium. The brand you like is probably available with no problem.
The problem is that there are several filters that will screw on the late model mount. They range in height for some Volvo models of less than 2" to nearly 5" for the Chrysler v8. Obviously a tall version is going to have more filter area, a lower flow rate through the filter matrix and as a result have less pressure drop, longer life with the increased filter area, and probably better filtering with the reduced pressure drop across the filter, as compared with a short version with much less filter area.
Barry
Barry Parkinson

Fletcher, Thanks for the information, I didn't buy it to use, I have been cutting some new filters and wanted to see what was inside. Someone on MGB Experience had a low oil pressure problem with a Bosch filter a few days ago. He bought it at Auto-zone. I bought a Bosch 3321 from Auto-zone last year, it was listed as as correct for a MGB. It's also very short. I don't know if my photo link will work for everyone it's in Yahoo photos
http://new.photos.yahoo.com/flash1929/album/576460762381800884/photo/294928803249763665/34

Clifton
Clifton Gordon

Thanks for the information, I'll keep a closer eye on the type filters used in the future. Filtering the air and oil will be easy, it's filtering out the morons that worrys me. ;-)
Bill Young

anyone ever cut down the stand pipe by 1/2"?
JohnB

John B-
Why? So some idiot can put an even shorter filter on and repeat the process? Or maybe so more oil would drain out and have to be refilled before you got pressure? The first cars with that filter setup did not have the standpipe at all, and they rattled like crazy until they filled the filter. I actually made a standpipe for one of those, before the factory thought of it. For the same reason, bigger filters are not a good idea. Just get the right filter, or something close, they're not hard to find.
Note that the internal support has to do with the drain back/relief valve, so bending it can cause other problems - not that it matters after you go a ways with no oil flow!
FRM
FR Millmore

After reading the chain of responses I noticed there was not much mention of which filters are actually correct and have a good track record. There was a mention of the NAPA Gold 1068, but no others.

I'm running a Fram on my 72B which had a Puralator something on it to begin with - that had to be pryed off with a bar through the filter and 2 guys pulling/pushing bar. I expect it hadn't been changed for awhile.

So, is there a list of filters that are reliable for Bs?
R.W Anderson

RWA-
There's plenty in archives on this, complete with numbers for many different filters, look it up. Good application/full catalog books from manufacturers are easily available, and all have cross reference to other mfrs. Local auto parts stores will usually give you one from, say, Fram or Purolator. It is still wise to check basic dimensions (also in mfrs book), until you KNOW which ones are right. The common web parts listings today really suck for old/obsolete/unusual apps. See adjacent thread on Mann W917, a very good choice, comes from Volvo suppliers. I formerly used Fram, but the quality is poor today, so no more. NAPA gold is a premium Wix or maybe Hastings, with similar or identical numbers, also very good. "Very good" assumes correct application!!!
PS I am still waiting for pics and discussion from you on the top fitting problem! You started that one, so I expect a response. Email above.
FRM
FR Millmore

FRM,
Isn't the airflow dependent on the route the air has to take to get into the filter rather than the filter size itself? With the non-standard it's the little holes, with standard (SU) filters then the restriction is the inlet tube...
Neil
Neil

RWA. I have been spending part of my spending allowance on new oil filters to cut open for about a year. Based on my observation, not scientific but just a visual observation of the component quality I would use the following filters. As mentioned NAPA Gold 1068, Wix 51068, same as NAPA, Motorcraft FL 300, AC Delco PF 13, Purolator Pure 1 PL 14670, Purolator Premium Plus L14670, Mobil 1 M204 and K & N HP 204. The Mobil and K & N are the same filters internally but their filter elements are smaller than the above mentioned filters and they are costly. I'm sure there are others including Mann but I haven't examined them. Others I have looked at but wouldn't use are Bosch, Walmart, Fram and STP. They all look to be of poor quality and in the case of Bosch too short.

Clifton
Clifton Gordon

Neil-
It's like everything else, Yes, but...
The flow through the little holes, or what there is of it, is at very high speed and large pressure drop. That gives poor flow and terrible filtering.
The flow through the snorkels is somewhat restricted, though far less than with the holes, but this is compensated by the needle selection; the OE needles are only right, or close, with the filters in place. The point of the snorkels is first to accelerate the airflow beyond supersonic levels, meaning that noise is literally sucked into the engine, since the air goes in faster than the sound goes out (sound only travels in the air). This is a big issue since the advent of noise regs, and it is illegal by US Federal law to alter or modify the air intakes on modern vehicles for this reason. The second effect is that large bits of crud are centrifuged out of the airflow and fall to the bottom of the filter case, or are buried in the filter where the air hits it. That leaves the rest of the element clean to get out little bits, and the airflow is now slow with a small pressure drop, so it flows well and cleans the air nicely.
Some cars, like XKE, will not pull the hat off your head at high engine speeds without the air filter snorkels in place. I used to routinely test to 6000 redline in third, and without the snorkels they would not go over about 4800.
The snorkels on MGB are primitive in the extreme, it is far better to have a radiused entry as in good carb inlets, and all modern vehicles have that. It would likely call for revised needles if you modified them in that way. It always mystified me that the MGB filter backplates were the best in the production world, with their nice radiused entry, but the filter snorkels were so crude. I guess it just spoke to a different guy spec'ing the carbs, compared to he who did the filters. You will note that MGB filter cans have the tubes tangential, to give the centrifuge effect. Spridget ones do have the radius entry, and the more desirable tapered profile, but those are centered, so they don't centrifuge, and just drive the dirt into a small area of the element. And, the Spridget ones do not have the nice radius entry backplates! Go figger!
FRM
FR Millmore

FRM, Excellent discussion about filters, really getting an education. Was not aware that the stock MGB filter cans created a centrifuge effect. I have always owned Spridgets and am aware of the dirt collected in one area. I was considering for my B the stock paper filter with the stock baseplate but with just a flat cap on top, open sides. Wonder if this is going to seriously affect my engine performance?
Mike
MK Mike

Mike-
It will be noisier. It will likely go somewhat lean as the speed goes up, possibly enough to cause problems. If it noticeably affects performance, it's because it's way lean on top, and that leads to fried pistons if you keep it wound up for long. Seems like a nuisance to sort new needles if that's all you change, but if you do other mods so you need new needles anyhow, why not? Filtering won't be compromised all that much, though water could be more of an issue; we used to sometimes have trouble on Volvo 122 with exposed filters getting wet in heavy rain or snow. Took a while to figure out why they acted rich in wet weather, since they would be dry when they got to the shop, but one came in frozen solid one nasty winter day.
The centrifuge effect is elegant (and free!), used in a much more developed form on heavy equipment engines in dirty environments, to take out most of the dirt before the filter element proper. Even big truck filters have the air passing through a set of "turbine" vanes before the element that cause similar action. You have to empty the case periodically, but the elements last a good while.
FRM
FR Millmore

This thread was discussed between 13/03/2007 and 16/03/2007

MG MGB Technical index

This thread is from the archive. The Live MG MGB Technical BBS is active now.