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MG TD TF 1500 - Mark IITD Air Filter

I know this has been often discussed before, but I get probably a letter a month, asking just what was original. Thanks to Nick Herweg, I have a bit more authoritative information, and so here is my most recent reply to the MG Experience:

There is still plenty of discussion on this point, but I am confident I know the answer (famous last words...).

The TD NEVER had individual pancakes, not the regular TD nor the Mark II. Many cars have ended up with them, either the chrome POS now sold by Moss (formerly Helling and Stelling), or the TF Vokes air filters.

Regular TDs had H2 SU carbs, with a roughly T-shaped air intake pipe, and an 8 (I think) oil bath oil filter. I believe strongly that early (up to mid-1952?) Mark II TDs came with this SAME air filter set-up as regular TDs. There were some problems with it, however. The carb flange bolt holes on the 1-1/4 TD carbs is different from the 1-1/2 H4 Mark II carbs, so to make them fit , the carb flange holes were fairly roughly filed inward with a round file at the factory, to make the filter fit. But the resulting problem was that this small air filter set-up limited the revs of the engine because it simply could not pass enough air. Read the road test by Tom McCahill in Mechanix Illustrated to hear his frustration!

Here is an eBay listing for the regular TD/early Mark II air filter unit:

Later Mark II cars had an entirely re-cast air intake tube looking just the same but with with larger ports - and used a larger 9 oil bath air filter, with a slightly different shape. Because the ports were wider, the carb flanges no longer needed to be filed inward. Here is an eBay entry for an original car with the larger unit:

Why do I say this?
1) Mark II TD carbs are found with either elongated holes on the carbs, or regular round holes. Admittedly, carbs are swapped around not infrequently, but the majority of early cars (and un-restored cars) have elongated holes, later cars (including unrestored cars) have round holes.
2) There are so many cars with the elongated holes that the need to modify carbs must have lasted a long time, and also there is NO reason why an individual would do that to so many early cars; it must be factory work. It is rough enough work that it must have been assembly-line modification, and not an SU modification.
3) Also, in Feb. 1952, the MG factory sent out a letter to dealers as Service/MG/NO.71 on this subject, parts of which I quote here:
TD Mark II Engine Performance
Preliminary investigation into the complaint of low maximum RPM on this model have shown that this is to be due to too rich a mixture at full throttle.
Some support is thus given to the theory that the air cleaner is too small, and whilst if this were true a very similar condition would arise, it is not possible;e at this stage to be at all conclusive...
With regard to the suggestion that true maximum RPM can be obtained by removing the air cleaner... we must also stress that running without the air cleaner is very much deprecated and we cannot be held responsible under the guarantee for excessive wear arising from this practice...

This letter notes that (as of 7 Feb., 1952) Mark II cars are now leaving the factory fitted with EM needles, but with a pair of the LS1 needles used previously,taped to the air intake pipe the factory was clearly unsure what to do, and they were hedging their bets. The standard TD needles are ES, and are leaner across the board. EM needles are a bit richer, but LS1 needles are richer still. This says to me that rather than get more air in,the factory cut back on the richness so the car will run better (but unspoken is that performance will no doubt be diminished). I believe they solved the problem by making the larger air intake pipe and oil bath air cleaner, but only near the end of the production run.

So whats right on a Mark II today? Pancakes are not. Technically, for carbs with elongated slots, the earlier TD air filter unit is correct, BUT will strangle the performance. Later cars have the larger set-up, and performance is SLIGHTLY improved, but these systems are damned rare I dont even have an original 9 oil bath. ANY engine runs better with no air cleaner at all, but thats not good for the engine. My best suggestion for a TD Mark II driver is to run TF Vokes filters when you drive the car, and have an original set-up you put on for shows, if you want to demonstrate originality.

Tom Lange
MGT Repair
t lange

Tom McCahill test drove the MG TD for Mechanix Illustrated. He basically beat the hell out of it, and compared both the standard TD with the TD/C. He soon found the TD would gain ten MPH if the air cleaners were removed. He discussed the poor airflow of the elephant snorkel and the oil bath AC filter. This design flaw was well known, and many people removed the factory filter in persuit of better performance. This is why many TDs do not have the factory snorkel anymore.
I too am not aware of any other filter from the factory. I agree with Tom that a correct TD or TD/C should have the elephant snorkel and AC filter, with later TC/C cars having the larger filter and snorkel assembly.
If you want to drive your TD and enjoy it, take the factory filter off and fit TF filters with K&N filters. If you want awards and 100% correctness, install the original factory mistake, ur, um, filter.
D. Sander

I put high efficiency air filters on my TD and had noticeable improvement in running and power. These are Ram-Air filters which offer much more surface area (and therefore breathing) than pancakes OR the original setup.
I'm just keeping the original manifold and bath for times when I want to look original.

Geoffrey M Baker


Excellent post.
I couldn't agree more.
Unfortunately, there is much misinformation out there and some rather widely circulated material seems suspect.
The confusion is further complicated by the fact that many of our cars are not entirely original, a reality we are sometimes reluctant to accept.

Your explanation is spot on.

Best regards, Steve
Steve Swarts

Thanks Tom, for that superb piece of research!

Dave Braun

Tom, I have a spare MK II 9 inch air cleaner if you are looking for one. Call me at 540-907-2583. MGTDC-22679.
Forrest Rubenstein

Hello Tom. Is the attached picture what you are talking about?


R Taras


Thanks for these details!

Although I have an early TD/C with the carb holes elongated for the regular air filter, I'd like to find the enlarged air cleaner set-up used on the later cars.

Charlie Adams
Charlie Adams

Yes, Butch =- that's the larger 9" air filter. Interested in selling it? I have a late TD/C (burned CA car...) that it would go on.

t lange

Whilst trying strenuously to avoid being a member of the OP, was the label found on the air cleaner originally?

I had some memory of it being on only the smaller cans and for a limited period of the run.
Ian Bowers

Tom, mkII air cleaner assembly packed and will put in mail monday morning. Forrest MGTDC-26679
Forrest Rubenstein

Ian - I understand your thoughts perfectly. Based on my own experience, I have seen fragments of the original tatty paper label on a very few unrestored TDs, but have seen too few ORIGINAL Mark IIs with proper 9" oil bath filters to be able to say - and I have never seen an original Mark II with a label in place.

I'll also inquire of the more knowledgeable Mark II people than I.

Tom Lange
MGT Repair
t lange

I bought the TDII in 1964 when it was approaching 11 years old. The snorkel and air cleaner had been detached, the PO said, for some time before.

The air cleaner finish is untouched since then, and there was, nor can I now find any trace of a sticker. I would therefore put a high probability on it never having been part of the car's decoration from leaving the production line.

However, someone may know different ... !
Ian Bowers

Pages 77 and 78 of the Graham Robson book "The T-Series MG's" have, what seem to be factory or at least period photographs of a complete Mk II engine.
They clearly show a decal or sticker on top of the air filter....
Just my 2 cts.

Nick (TD3232)

Nick Herwegh

...and the other one:

Nick Herwegh

Yes, Tom I'd be interested, contact me off site.

R Taras

This thread was discussed between 27/10/2015 and 02/11/2015

MG TD TF 1500 index

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