Lotus Elan Central
Replacing CAS Oil Seal

If you are suffering from oil leaks which appear to be coming from the mating face of the cylinder head and block just below the Cam Angle Sensor, don’t despair! It is likely that oil is coming from leaking O-rings in the cam cover and not the head gasket.

Apparently, early in the car's life, Lotus dealers were replacing lots of head gaskets to cure this problem before the factory issued a technical bulletin to confirm that the O-rings were the source of oil leaks in this area.

The fix is for this is simple and quick and certainly worth while before investigating other potential (and more costly) sources of oil leaks.

Parts Needed:

  • 2x Cam Seal O-rings – (Lotus part number: LA 100E65625) (Cost approx. £3.65UKP each plus tax)
  • Small quantity of gasket sealer/mastic

Tools Needed:

  • 6mm allen key
  • 10mm socket wrench with short extension bar
  • Paperclip and timing light for re-setting the ignition timing (see text)


There are two seals to replace, one of which is located behind the CAS on the shaft that connects to the camshaft. The other is located behind a plastic bung adjacent to the CAS at the bulkhead end of the cam cover.

Tackling the CAS seal first, locate the 6mm hex bolt which retains the CAS against the mounting bracket and mark the position of the CAS against this bracket. This will make re-setting the timing easier after the CAS has been removed and replaced.

Undo and remove the 6mm hex bolt and pull the CAS out of it’s housing. You will see the offending O-ring on the shaft attached to the CAS. Simply remove this and replace with your new O ring, a little oil smeared lightly on the gasket will ease the fitting.

Clean the cam housing before replacing the CAS, you will see that there is only one position for the CAS shaft to go back in as it locates on a semi circular cut-out in the cam shaft. Rotate the CAS shaft to line it up with the drive in the housing before pushing the CAS back into position. Again ease this with a little oil on the O-ring as it will be a snug fit.

Replace and tighten the hex bolt, lining up the marks you made on the CAS and mounting bracket.

The second O-ring is located behind a black plastic D shaped bung adjacent to the CAS, towards the rear of the cam cover. This bung is not easy to see as it is obscured by sensors in the cylinder head, electrical connections a water pipe and probably a few years of leaking oil and grime.

Firstly remove the electrical connectors from the sensors in front of the bung to give you clearer access, then clean the area around the bung (spirit cleaner and a paintbrush make easy work of this). Once clean you will notice a 13mm bolt head at the bottom of the bung, you can remove this with a socket on a short extension bar (or 13mm open ended spanner). It’s a bit of a struggle getting good access to this but it is possible without having to remove either the water pipe or sensor.

With the bolt removed the bung will come out of the cam cover and you will have a chuckle at the fine solution the engineers came up with to keep the oil from spewing out of the hole in the cam cover. After that simply clean up the bung and the cam cover, remove the old O-ring and pop on the new one. Smear a little gasket sealer on the O-ring and push the bung back into the cam cover, take care not to over tighten the bolt in the alloy cam cover, then reconnect the electrical connectors.

You have now cured your oil leaks, the only thing left to do is to check the timing following the procedure outlined in the ‘Setting Engine Timing’ section and away you go. You must reset the timing as minute differences in replacement position will have a big effect on base engine timing!

Replacing both O-rings should take around ½ hour, and with re-setting the timing you should allow around an hour for the whole job. (sounds like pro mechanic time to me; I would bet twice that long for each procedure for us laymen!--Doug)

- write-up by Bryn

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