The first 907 normally aspirated engines that Lotus manufactured used studs to secure the camshaft housings to the cylinder head.
This method of fastening was used up until the introduction of the later high compression (HC) engine in mid-year 1985.
At this point Lotus replaced the studs with an "anti-tamper fastener" in the form of an 8mm Torx headed bolt.
This Torx fastener, Lotus part number B911E1311F was used to secure the exhaust cam housing A912E2033K and inlet cam housing A912E2034K.
Both of the camshaft housings were used in versions of the 910 HC turbo-charged Esprit engine plus the 912 HC normally aspirated Excel engine.
It is not unusual to experience problems when attempting to extract the Torx fasteners.
Extraction problems are often compounded and manifest themselves in the following ways -
1) Damaged Torx fastener head which is the result of the socket slipping
This is caused by poorly designed and ineffective head to socket interface.
The fastener head has conical flanks that disengage and slip when coated by a residual film of engine oil.
2) An excessive extraction torque is often experienced when attempting to remove the Torx fasteners.
This is caused by anaerobic sealant (used between the cam housing to head junction) seeping into the threaded fastener holes.
The surplus sealant acts as a thread-locker and is often found on the threaded section of the fasteners when they are removed.
3) Cylinder head threads are damaged or pull out whilst the cam housing is being installed.
This problem is caused by the fact that the Torx fasteners are too short for the application.
From experience there appears to be 3 or 4 installation cycles before thread failure occurs.
A worse-case scenario can be experienced when a cam housing threads pull out whilst installing a cylinder head on an Esprit engine whilst still in the vehicle.
Experience has shown It has been necessary follow a routine pre-installation procedure on every 910 HC and 912 HC cylinder head
This involves torque-testing every 8mm Torx fastener hole prior to final installation of the camshaft housings - see photo immediately below
Torque testing the threads IS NOT an absolute guarantee they will not fail during the next fastener installation.
Unfortunately there is no way of knowing how many times the cam housings have been removed and threads cycled.
One solution is to install Keysert locking thread inserts at all 16 threaded holes that the Torx screws locate in.
This remedy involves drilling, tapping, and then screwing in the Keysert followed by a punching operation to activate the 4 locking pins..
Estimated cost for doing this is $20/hole = $320 dollars which is more expensive than replacing the fasteners.
The solution to this problem is to install a slightly longer fastener to engage fully in the pre-existing threads within the cylinder head.
Changing to an after-market fastener with a small 10mm hex head solves both problems and ensures a quality result every time.
From experience, the later HC cylinder heads are machined so they may accept the original studs so there is usually plenty of thread depth.
However the thread depth should be check prior to installing and then torquing the longer fasteners.
Vehicle application = Lotus Esprit S3 HC, Esprit S4 and S4s plus Excel HC
Fastener kit (16 bolts) weight = 366 grams
Kit contains 16 bolts, sufficient to install both cam housings @ $112.00 plus GST
Please note carefully, pricing above does not included postage and packing.
Pricing information is correct as of 30/9/2018 but may alter with time and currency exchange rate fluctuations.
To order your suspension bush kit, send us your parts order today
Shipping from Australia to UK, USA, New Zealand, anywhere worldwide!
Contact Lotus Marques now for postal or courier shipping costs.
This method of fastening was used up until the introduction of the later high compression (HC) engine in mid-year 1985.
At this point Lotus replaced the studs with an "anti-tamper fastener" in the form of an 8mm Torx headed bolt.
This Torx fastener, Lotus part number B911E1311F was used to secure the exhaust cam housing A912E2033K and inlet cam housing A912E2034K.
Both of the camshaft housings were used in versions of the 910 HC turbo-charged Esprit engine plus the 912 HC normally aspirated Excel engine.
It is not unusual to experience problems when attempting to extract the Torx fasteners.
Extraction problems are often compounded and manifest themselves in the following ways -
1) Damaged Torx fastener head which is the result of the socket slipping
This is caused by poorly designed and ineffective head to socket interface.
The fastener head has conical flanks that disengage and slip when coated by a residual film of engine oil.
2) An excessive extraction torque is often experienced when attempting to remove the Torx fasteners.
This is caused by anaerobic sealant (used between the cam housing to head junction) seeping into the threaded fastener holes.
The surplus sealant acts as a thread-locker and is often found on the threaded section of the fasteners when they are removed.
3) Cylinder head threads are damaged or pull out whilst the cam housing is being installed.
This problem is caused by the fact that the Torx fasteners are too short for the application.
From experience there appears to be 3 or 4 installation cycles before thread failure occurs.
A worse-case scenario can be experienced when a cam housing threads pull out whilst installing a cylinder head on an Esprit engine whilst still in the vehicle.
Experience has shown It has been necessary follow a routine pre-installation procedure on every 910 HC and 912 HC cylinder head
This involves torque-testing every 8mm Torx fastener hole prior to final installation of the camshaft housings - see photo immediately below
Torque testing the threads IS NOT an absolute guarantee they will not fail during the next fastener installation.
Unfortunately there is no way of knowing how many times the cam housings have been removed and threads cycled.
One solution is to install Keysert locking thread inserts at all 16 threaded holes that the Torx screws locate in.
This remedy involves drilling, tapping, and then screwing in the Keysert followed by a punching operation to activate the 4 locking pins..
Estimated cost for doing this is $20/hole = $320 dollars which is more expensive than replacing the fasteners.
The solution to this problem is to install a slightly longer fastener to engage fully in the pre-existing threads within the cylinder head.
Changing to an after-market fastener with a small 10mm hex head solves both problems and ensures a quality result every time.
From experience, the later HC cylinder heads are machined so they may accept the original studs so there is usually plenty of thread depth.
However the thread depth should be check prior to installing and then torquing the longer fasteners.
Vehicle application = Lotus Esprit S3 HC, Esprit S4 and S4s plus Excel HC
Fastener kit (16 bolts) weight = 366 grams
Kit contains 16 bolts, sufficient to install both cam housings @ $112.00 plus GST
Please note carefully, pricing above does not included postage and packing.
Pricing information is correct as of 30/9/2018 but may alter with time and currency exchange rate fluctuations.
To order your suspension bush kit, send us your parts order today
Shipping from Australia to UK, USA, New Zealand, anywhere worldwide!
Contact Lotus Marques now for postal or courier shipping costs.
