XPAG rear oil seal again

My friendly MOT tester looked censoriously at the growing oil patch deposited by my TC on his clean tiled floor and as he spread sawdust over the offending pool, commented that new regulations limit the acceptable pool size from leakage to 75mm dia. after 5 minutes of running the engine. I made a mental note of making sure the engine oil was not too hot before my next MOT.

Now that most T -Types are cherished and kept in a garage, the need for an inbuilt oil-spray chassis preservation facility is almost redundant. So, mindful of the rear engine oil seal kits available for the XPAG, I relished the chance to help a friend renew his existing oil seal and learn about any issues.

The existing oil seal had been reasonably effective for many thousands of miles even without a “speedisleeve”; however, we decided to upgrade the rear seal during the course of an internal engine inspection/partial rebuild. This inspection was brought about by the engine consuming some water due to the splash created by the front wheel being driven into a deep rain filled pothole. The ensuing steam produced in No.3 cylinder blew the head gasket and did a great job of cleaning the top of the piston.

A new “we’ve carefully selected this one” oil seal was purchased from the supplier of the original kit and, as advised, we also decided to use a 1mm spacer between the housing and the oil seal to help reposition the lip of the new seal inwards from the edge of the crankshaft’s flange. Looking at the setup certainly revealed that the seal’s lip would be running very close to the chamfer on the crank flange’s edge.

The new seal lasted a few hundred miles before a referral to a hospital urologist was evident. After dismantling the engine yet again, the seal appeared sound, if not a little stiff. However, we then noticed the absence of any “garter spring”; this helps maintain pressure of the lip on the crank’s flange. A further revelation concerned the profile of the seal’s lip. Without the garter spring, the contact point of the lip sits at the very edge of the oil seal’s profile and consequently could run on the chamfer of the crank’s flange, (see Fig. 1). Adding a garter spring modifies the profile of the seal’s lip by moving the contact point away from the edge of the seal and consequently away from the chamfer on the crank’s flange, (see Fig. 2).

Searches for a replacement imperial oil seal with a garter spring, only turned up a Nitrile 3.75” x 4.75” x 0.375” seal. However, the maximum rated peripheral velocity for Nitrile is only 14 m/sec. which roughly corresponds to 3,000 rpm and this value is probably reduced at higher temperatures.

The alternative Viton seal would be rated at 40 m/sec. but couldn’t be found in the imperial sized seal we thought we needed. Then the penny dropped, thanks to an article from the Y Register; an almost equivalent Metric seal 95 x 120 x 12 mm could be used. The crank’s flange is actually metric at 95 mm dia. which is 3.74”, some 10 thou. under the 3.75” of the imperial seal. The housing for the imperial seal is 4.75” in dia. which is 120.65 mm, some 25 thou. greater in dia. than the 120 mm dia. of the metric seal. However, the width of the metric seal is 12 mm – over 2 mm wider than the 0.375” (9.52 mm) of the imperial seal. This meant a machining operation to remove over 2 mm. from the face of the flywheel adjacent to the seal (see photo 1.)

Photo 1 – removing over 2 mm. from the face of the flywheel adjacent to the seal.

Unfortunately, such an operation would also remove the counter-bored section of the flywheel that helps locate the crank’s flange. Not an ideal  situation, although I was able to leave a thin lip about 1.3 mm thick and 2 mm. high around the edge that helped location and could be accommodated within the oil seal. The crank/flywheel dowel pins and bolts will now have to take on some additional duty of location. We decided to retain the 1 mm spacer and fit a “speedisleeve”, despite the crank’s flange being smooth, as we hoped it would provide a small extension over the chamfer on the crank’s flange.

The outer diameter of the seal was secured in the slightly oversized housing by a heavy-duty sealant.

As the lip of the seal faces forwards, there’s some concern that sliding the seal over the edge of the “speedisleeve” might damage the seal’s lip; this can be resolved by using a tube-like guide made from a thin plastic sheet to cover the “speedisleeve’s” edge. Don’t forget to lightly lubricate the “speedisleeve” with some Vaseline.

There are two widths of 95 mm “speedisleeve”, 8.74 mm and 21 mm – the 8.74 mm. wide version is suitable and is inserted with the “speedisleeve’s” detachable rim, trailing behind for this particular application. The “speedisleeve” is initially forced on to the crank’s flange using a wooden buffer against the rolled-up edge of the “speedisleeve”. This is then lightly tapped with a hammer, ensuring it goes on square. The final location of the “speedisleeve’s” leading edge just covering the chamfer needs the “application cup” to engage the underside of the rolled-up edge, which again is lightly tapped. The rolled-up edge is then cut off along its fault line with a sharp blade, not an easy task. The exposed edge of the “speedisleeve” should then be de-burred with some emery cloth or a needle file.

With all the procedures faithfully carried out, we were disappointed to observe that oil still dripped from the bell-housing, but at a much reduced rate of one small drop every 15 seconds when hot. 20 odd drops during the MOT test specified time might just be acceptable, but won’t do anything to encourage the kindly disposition of the tester. Bring some sawdust just in case.

Viton oil seal……95 x 120 x 12 mm. R21/SC Viton. Bearing-King.co.uk at £17.34

Speedisleeve….95 mm. SKF CR99374 from £33, try Barnwell.

Heavy duty sealant…..Victor Reinz Reinzosil,  Available from e-bay at less than £5 for slightly out of date 300ml tube.

However, the drip rate soon started to increase, so out came the engine again and on loosening the two socket cap screws clamping the two halves of the seal’s housing together, the seal was found to be not that secure. Whilst we recognised that the imperial housing was about 25 thou. greater in diameter than the metric oil seal, we assumed that laying a generous fillet of sealant in the housing would secure the seal. It seems the seal should be physically clamped by being an interference fit in the housing, otherwise a loose fit could result in an offset of the seal’s axis and any induced movement of the seal could degrade the effectiveness of the sealant.

A cunning plan was hatched to introduce a 12 thou. shim around the periphery of the seal, which would set up a similar interference fit as found with the imperial seal when the housing was clamped together. This revealed a new problem due to the open end of the seal being located in the housing, whilst the robust closed end was almost 4 mm proud of the housing. The interference pressure on the open end of the seal from clamping the two halves of the housing tended to squeeze the seal out of the housing (see Fig. 3), somewhat reducing our confidence in how the seal is retained.

This rather worrying development caused us to re-consider how we might secure the seal; two decisions were made. (1) To use a thinner shim made from two 6 thou. strips of “wet and dry” abrasive paper stuck to each half of the housing with super glue and (2) To make up a retaining disk that would hold the seal in place, the disk to be bolted to the housing by 6 M5 countersunk screws, positioned to avoid the housing’s clamping fixture, (see photo 2 below).

The disk was cut out from hard aluminium 4mm sheet and then machined on a lathe, (see photo 3).

Photo 3 – machining the disc which had been cut out of hard 4mm aluminium sheet.

The inner dia. was shaped to cup the outer edge of the sleeve and assembled with a fillet of sealant in the cup, (see Fig.4 previously shown alongside Fig. 3). The additional projection of the disk meant further machining of the flywheel to give clearance.

After the engine was reinstalled and the oil pump primed, we ran the engine until its operating temperature was achieved, what a relief when there were no signs of leakage. After the bonnet, ramp plate, floor boards and seats were put back, the engine was run again but this time a steady drip every 22 seconds developed. We were banking on being third time lucky as we felt all the possible issues had now been addressed, such as selecting the Viton oil seal with a garter spring, using a spacer and speedisleeve and fitting a retaining/sealing support.

As you can imagine we felt bewildered, where have we gone wrong? There are conflicting views on the oil seal conversion, so what are the variables that decides its effectiveness? Others have been successful with some kits, often mentioning attention to detail.

Could the oil held back by the oil seal, overload the “bleed hole” that allows oil to drain back into the sump? Such an overload, caused by a worn rear main bearing, may be too much for the oil seal.

The latest offering for the oil seal is based on a graphite loaded PTFE version, which is capable of handling 12,000 rpm.

At 12,000 rpm, oil leaking from the rear oil seal would be the least of your problems!

Eric Worpe


After the above whimsical aside we had hoped to forget things, but the frustration from the poor outcome encouraged further investigation. We discovered that the oil seal housings fail to replicate the Archimedes scroll facility previously provided by the Mazak “oil thrower”. The reason being the need to allow some oil to lubricate the oil seal. As if that was ever going to be a problem!

Looking up specifications on oil seals, we found that SKF have taken over Chicago Rawhide and offer a 223 page technical brochure in which we learnt that PTFE seals can tolerate dry running but need a hard surface to run on such as a “speedisleeve”. Given that the Archimedes scroll, even on its best behaviour, still allows some oil through and this combined with the tolerance of PTFE seals to run dry, the retention of the full Archimedes scroll facility now looks promising. This would need only a small change in the design of the seal’s upper housing.    

The second area of concern is the location of the bleed hole that allows oil to drain from the cavity formed by the seal and its housing into the trough in the rear main bearing cap, down the tube and into the sump. This 3/16” dia, hole is pitched just above the seal as opposed to being adjacent the seal. This means that when static, the lower part of the seal sits in an oil bath. However, more concerning is the dynamic situation. The crank’s flange sits between 1 and 2 mm away from the housing, so what effect has the whirring flange, so near the bleed hole entrance, on the ability of the bleed hole to drain away any oil? We also wondered if the seal could be overloaded by the whirring flange centrifuging oil into the chamber formed within the seal itself.

Unfortunately, the location of the bleed hole is constrained by the dimensions of the rear main bearing cap Fig. 5, so improving this issue is unlikely. Perhaps future housings for PTFE seals could reintroduce the Archimedes scroll.

8 thoughts on “XPAG rear oil seal again

  1. David B Smith says:

    When the need arose to change the oil seal after 12000 miles we did it without removing the engine (TF) and made up 2 legs bolted to the lower bell housing to take the weight of the engine on the chassis rails after removing the gearbox. The original conversion had included a Speedisleeve. The motivation for the seal replacement was not the drip, which was no worse than that from most most XPAG engines but incipient clutch slip and the planned trip to the Isle of Man. The clutch slip was found to have been caused by oil seeping past the heads of the 4 bolts holding the flywheel then running along the gearbox first motion shaft and centrifuging onto the front face of the clutch plate. Lockdown happened the day after the job completed and IOM trip cancelled so haven’t done enough miles to know yet whether new seal is successful. I was fortunate in being able to use an old fashioned lift belonging to my local friendly garage.
    Sorry am not able to show a picture on this reply.

  2. Lawrie Alexander says:

    The Moss Motors seal kit sold in the USA (p/n 433-421) comes with 9 pages of illustrated instructions and – most importantly – a seal retainer centering tool. Engines which have been line-bored sometimes move the axis of the crankshaft to one side so using the original mounting holes for the bolts that secure the upper half of the retainer locates the seal sideways relative to the crankshaft flange. One engine I worked on (before developing the seal centering tool) had the seal flattened on one side of the crank and not touching the other side! The latest iteration of the 433-421 kit has resulted in a 90% success rate: no oil leaks after installation. The other 10% appear to be the result of crankshafts being reground off-center so that the rear flange actually oscillates. This makes the seal less than efficient (and probably messes up the engine’s balance with the flywheel oscillating, too).

  3. trevor Short says:

    Eric I have fitted a moss seal to my TD. the first one (ptfe type) started leaking after about 200k. On inspection the seal had a considerable warp in it and I suspect it had been damaged in transit to Australia. I searched for a replacemant but not available in Australia. A new seal arrived from England and it checked out ok . I was a little concerned about he way the PTFE seal is fitted. All the suppliers with this type of seal supply a fitting sleeve , none is supplied by Moss. So I machined up a fitting adapter so the seal went on without any manipulation.( Moss fitting instruction say– avoid seal puckering) Due to the seal failing I then looked at what I actually purchased. The clearances are at a premium, I think the flywheel location sleeve ended up at about 35 thou. enough but just enough, I follow you on the PTFE seal 1. they can run dry 2. they can run in oil. Due to the 3/16 return oil hole they will run in a reservoir of oil due to the height above the seal . And yes why don,t they now with the PTFE seal incorporate the old scroll seal, If ever the PTFE seal fails at least the pool of oil under the car will be tolerable until time is available to repair, The pool of oil of the seal failure was about 12 inches in diameter.

  4. Eric Worpe says:

    Thanks to the above for their interesting comments. The issue about alignment of the oil seal housing and the crankshaft could be resolved if the housing incorporated the counter oil scroll as provided by the Mazak casting. You’ll be delighted to know that I hope to submit a short post script on the oil seal housing if John allows it.

  5. Michael balahutrak says:

    I have just installed the seal and not enough run time to fully evaluate – BUT – in anticipation of flooding the seal area with oil and possibly creating a positive pressure in this area – I have drilled 2 additional holes – one on each side of the original drain hole to facilitate rapid pressure alleviation and oil draining – hope this will fo the trick

  6. Eric Worpe says:

    Hi Michael,
    You may have a good point, I’ve wondered if drilling the drain hole at an angle such that the spin direction of the crankshaft’s flange would encourage oil to be swept down the drain hole. The hole’s opening could also be made funnel shaped to offer a greater catchment area. I hope all this home spun theory thinking is treatable.

  7. Anton Piller says:

    I am the one, who in 2016 posted a thread on the International Y-Type Website about this topic and nearly got into trouble because of it. I had bought, many years back a rear oil seal kit from one of the big suppliers – could not remember from whom. When I eventually got around to fit the kit to my XPAG engine, I realised that the green coloured (Nitril?) seal would not work as it should: there was no garter spring with it and the sealing lip protruded over the chamfer on the crank flange’s edge. If a speedy sleeve was mentioned, it came across more like an optional extra.


    Because I was not happy about the lip seal, Igot in touch with a Swiss supplier of lip seals and settled for a brown coloured Viton type seal BAVI 95-12O-12. At the time, in 2016 pressure resistance was not a major topic for me – otherwise, I might have gone for a type BABSLVI seal with its pressure resistance of up to 10 bar..

    After my thread was published, both Moss and B&G contacted me and pointed out that they are using improved seals since a couple of years now. A MG mate gave me a copy of the (presumably uprated) very good B&G fitting instruction that, amongst other useful tipps, recommends to chamfer the aluminium retainer’s big centre hole to improve the oil flow to the seal and that they now incorporate superb graphite coated Teflon seals that withstand 12,000RPM / 600°F. I do not know what Pressure resistance it offers.

    I do not add a copy of the B&G Fitting Instruction because I am careful about copyrights…

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