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!
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.