Improving an Aftermarket Rear Crank Seal Kit

This article was written by Anton Piller in Switzerland and forwarded by Jerry Birkbeck.

It must have been about 20 years back, when I first saw an advert and read an article about these kits. Since I liked the idea and appreciated the engineering skill behind it, I bought two of the kits – one for my TD and one for my long-term project, YT4220. Both kits were fitted and what struck me at the time was, how close the lip of the oil seal was to the edge of the crankshaft’s shoulder and that it was not spring-loaded.

My expectations were running high and the TD was up and running soon, while the YT engine is still waiting to be fired up for the first time. Well, my high expectations were not really met and the engine still “lost” oil at the bottom hole of the bell housing (something that prevents the car from passing the very strict government controlled Swiss MOT).

By coincidence, I realised that the big spares suppliers nowadays include a round white plastic box with those kits. On enquiring, I found out that the box contains a so-called speedy sleeve that extends the crankshaft’s shoulder. Apparently, the kit’s manufacturer had found out, over time, that the seal’s lip runs too close to the crank’s edge and in some cases, cannot function properly (dependant on how big the shoulder of the chamfer is).

Crankshaft and flywheel removed and con rods secured by a length of dowel.

I decided to take the engine out of the YT, fit such a speedy sleeve and have the crank and flywheel balanced at the same time. Because of limited space in my garage, I asked the owner of my engineering shop, if I could strip the engine at his shop, which he agreed to. The man is very knowledgeable and did his own Group 2, Sport 2000 and Mini Cooper racing. When he saw the “in situ” rear crank seal kit, he nearly had a fit and told me that the kit could not function properly. Here is his reason why:

  1. The seal’s lip being too close to the crank’s chamfered edge (which of course will be overcome by fitting a speedy sleeve).
  2. The lack of a spring within the sealing lip that would prevent the engine’s internal pressure to blow out oil past the lip.
  3. The non-descript type of seal that looks as if designed for slow moving shafts of a machine but not for use in high revving engines. The correct seals for car engines are of the Viton (FPM) type. These FPM seals withstand temperatures of up to 220° Celsius, whereas standard oil seals only withstand 100°C, which is the boiling point of water. In addition FPM seals withstand a circumferential speed of up to 40 meters/second versus the 14m/s of “normal” Nitrile (NBR) seals.

To the left, the kit’s seal that lacks a spring loaded lip. To the right, the FPM seal with its spring loaded lip.

Since I could not find out what type oil seal is used with the aftermarket kits, I decided to make sure and use a FPM type seal together with a speedy sleeve, to hopefully get the results, I expected in the first place. Here is what I bought:

  • SKF Speedy Sleeve 95mm, order number CR 99369
  • Oil Seal 95-120-12, order number CR 99369

Because the newly acquired seal is two millimetres wider than the kit’s seal, two millimetres were skimmed off the flywheel’s raised front section and the seal was glued into the aluminium clamping-ring of the kit with black silicon sealant.

Two millimetres had to be taken off the raised section in the centre of the flywheel – in order to allow for the 2mm wider oil seal.

In theory, I have done everything right to keep my Racing Engineer happy and I look forward to test the upgrade sometime early next year. Keep your fingers crossed….!

Anton Piller
MG YT4220

7 thoughts on “Improving an Aftermarket Rear Crank Seal Kit

  1. Lawrie Alexander says:

    Anton’s comments are interesting and valuable. However,
    the current rear seal conversion kit offered by Moss Motors does contain a seal which is specially designed for high engine speeds and temperatures, as well as detailed instructions which enable the installer to deal with the many other reasons why the early seal kits did not work as well as they should have. After installing over 100 kits, I found that there are remarkably many dimensional variations between the various XPAG/XPEG engines which have to be taken into consideration to accomplish a leak-free crank seal.

    • Ian Thornhill says:

      The above is very interesting. I rebuilt my XPAG with a new ‘Billet’ crank so no ‘speedy seal’ and the rear seal leaked badly. I stripped the engine again, changed the seal. and it still leaked. I was able to source a Viton seal very similar to the above but only 10mm thick not the 12mm above. on my engine the supplied ‘Green’ seal lip ran right on the edge of the crank rim. the Viton seal runs well in from the edge. Its in the car but and will be started and run very soon. Time will tell if it sorts the problem!

      • Toni TDC 2211 says:

        Ian Thornhill’ mentions that he used a narrower (10mm) Viton oil seal than Anton. It would be interesting to know more about it.
        Ian please let us know the supplier, the make and the order number of the seal.

        • Ian Thornhill says:

          The seal has ‘SOG’ on it 95-120-10 it is has a dust seal as well as the main spring filled oil seal. I purchased some of them from ‘Eriks’ (

          They also sell a front crank seal in Viton but with a dust seal rather than the single lip more commonly available. the lead time was about 5-8 days but they were very helpful.

          if they will not ship abroad, I am happy to purchase and send out using Paypal if it helps.

    • Royston Goodman says:

      Hi Lawrie,
      Could you advise regarding the Main Bearing cap return oil pipe, I have been advised to shorten the existing pipe and cut at an angle, this to help drain oil away from the newly installed seal. Is this correct. Hope you can helf
      rgds Royston
      [email protected]

  2. Barry Wilson says:

    I recently rebuilt the engine for my 1953 TD. Bored out to 1400cc and supercharged. I fitted the new type seal following the instructions in the pack. Everything went very and no leaks. I am currently rebuilding a second older engine and have encountered several difficulties. The crank end flange had been stamped with the part number so this had to be smoothed off. Had to make a tool to make the speed sleeve go on the flange. I used sleeve adhesive to fit because of the previouse number stamp. Flywheel required machining to clear the lip seal. Proof will be when the engine fires up.

  3. ANTON PILLER says:

    Attention readers
    Please note that the Order Nr. of the oil seal reads BAVI 95-120-12
    Your scribe, Anton Piller

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