Are you looking to have an oil-tight Lotus twin can engine but the oil filler cap leaks?
There can be several reasons why an oil leaks originates from the oil filler cap and this includes the following items-
1) Broken retaining spring clip (see photograph of faulty filler cap below)
2) Broken, missing or loose locking pins inside cam cover
3) Broken/faulty internal cap seal
4) Distorted cap
5) Distorted cam cover oil filler neck
Any of these faulty items can result in hot oil escaping and making a mess on your engine.
The photograph below depicts two common problems associated with the early style oil filler cap.
The first and most obvious problem is the broken spring clip that is riveted to the underneath the cap.
This simple spring is responsible for engaging on two steel pins (180 degrees apart) located inside the oil filler neck at the rear of the cam cover.
The locking action of the “butterfly-like” spring appearance is brought about by the cap being rotated and the hidden pins engaging at both ends of the spring.
At the time of writing, the author has no knowledge of replacement springs being available so oil filler caps maybe repaired.
The other problem with this oil filler cap is the tired and distorted rubber sealing ring.
This sealing ring prevents oil escaping when the filler cap is secured in its correct position by the spring underneath.
The solution to the original problematic oil filler cap is to design a quality replica part that has a hidden integral oil seal.
Designing a faithful replica cap with a concealed threaded insert that’s oil-tight is made possible by using Solidworks 3D CAD software.
Reproducing the original “twist and lock” filler cap (Lotus part number 036E6018) requires careful measurement to replicate the subtle dome and knurled edge around the circumference.
The 3D software model of the cap allows a threaded insert to be incorporated into the design.
This ensures the two mating parts screw together and create an oil-tight seal.
These caps have been CNC machined from aluminium 6061 to produce a high quality part that is designed to last.
Installation of the new cap
The recipient cam cover needs to have the internal locking pins removed and the oil filler opening machined to accept the insert.
The threaded insert should be a light interference fit and be installed with Loctite 620.
Once the Loctite has cured, the polished cap is simply screwed into the cam cover where it takes on the appearance of the original stainless steel item.
Lotus Marques stocks a range of oil filler caps to suit the following Lotus vehicles-
Lotus Elan S1 – S4 and Sprint
Lotus Elan +2
Lotus Europa twin cam
Ford-Lotus Cortina Mk 1, 1558cc
Ford-Lotus Cortina Mk 11, 1558cc
Lotus Elite 907, 2.0Ltr
Lotus Eclat 907, 2.0Ltr
Lotus Esprit 907, 2.0Ltr
Lotus Esprit 912, 2.2Ltr
Lotus Esprit 910, 2.2Ltr including Hci
Part numbers for the various oil filler caps to suit the vehicles above are as follows-
Early domed cap (Lotus part number 036E6018)
Three eared cap (Lotus Part number A026E0415)
912 oil filler cap (from engine # 25190) ratchet type 38.7mm (Lotus part number A912E6965F)
910 oil filler cap (prior engine # 25190) not ratchet type 38mm (Lotus part number A910E6779F)
Copyright © 2026 Lotus Marques
There can be several reasons why an oil leaks originates from the oil filler cap and this includes the following items-
1) Broken retaining spring clip (see photograph of faulty filler cap below)
2) Broken, missing or loose locking pins inside cam cover
3) Broken/faulty internal cap seal
4) Distorted cap
5) Distorted cam cover oil filler neck
Any of these faulty items can result in hot oil escaping and making a mess on your engine.
The photograph below depicts two common problems associated with the early style oil filler cap.
The first and most obvious problem is the broken spring clip that is riveted to the underneath the cap.
This simple spring is responsible for engaging on two steel pins (180 degrees apart) located inside the oil filler neck at the rear of the cam cover.
The locking action of the “butterfly-like” spring appearance is brought about by the cap being rotated and the hidden pins engaging at both ends of the spring.
At the time of writing, the author has no knowledge of replacement springs being available so oil filler caps maybe repaired.
The other problem with this oil filler cap is the tired and distorted rubber sealing ring.
This sealing ring prevents oil escaping when the filler cap is secured in its correct position by the spring underneath.
The solution to the original problematic oil filler cap is to design a quality replica part that has a hidden integral oil seal.
Designing a faithful replica cap with a concealed threaded insert that’s oil-tight is made possible by using Solidworks 3D CAD software.
Reproducing the original “twist and lock” filler cap (Lotus part number 036E6018) requires careful measurement to replicate the subtle dome and knurled edge around the circumference.
The 3D software model of the cap allows a threaded insert to be incorporated into the design.
This ensures the two mating parts screw together and create an oil-tight seal.
These caps have been CNC machined from aluminium 6061 to produce a high quality part that is designed to last.
Installation of the new cap
The recipient cam cover needs to have the internal locking pins removed and the oil filler opening machined to accept the insert.
The threaded insert should be a light interference fit and be installed with Loctite 620.
Once the Loctite has cured, the polished cap is simply screwed into the cam cover where it takes on the appearance of the original stainless steel item.
Lotus Marques stocks a range of oil filler caps to suit the following Lotus vehicles-
Lotus Elan S1 – S4 and Sprint
Lotus Elan +2
Lotus Europa twin cam
Ford-Lotus Cortina Mk 1, 1558cc
Ford-Lotus Cortina Mk 11, 1558cc
Lotus Elite 907, 2.0Ltr
Lotus Eclat 907, 2.0Ltr
Lotus Esprit 907, 2.0Ltr
Lotus Esprit 912, 2.2Ltr
Lotus Esprit 910, 2.2Ltr including Hci
Part numbers for the various oil filler caps to suit the vehicles above are as follows-
Early domed cap (Lotus part number 036E6018)
Three eared cap (Lotus Part number A026E0415)
912 oil filler cap (from engine # 25190) ratchet type 38.7mm (Lotus part number A912E6965F)
910 oil filler cap (prior engine # 25190) not ratchet type 38mm (Lotus part number A910E6779F)
Copyright © 2026 Lotus Marques
