V8 Cambelt Tensioning
Guide to checking cambelt tension (NOT covering setting cam timing)
by Mike S
The Lotus 918 is an interference design engine, meaning that it is possible for the valves to contact the pistons if correct cam timing cannot be maintained. With this in mind, great care must be taken when setting cam timing and adjusting tension belt tension.
Lotus recommend that the cambelt tensioning be checked on an annual basis. The operation of measuring/adjusting the belt tension (frequency) is not very difficult, but is eased significantly by the use of some specially designed tools.
Details are available in Section ED of the Lotus Service Manual.
Removing & Replacment
This job should take about 2 hours, but may take upto 5 hours if you are not familar with it.
You will need the following parts:
You will need the following tools:
The first job was to remove the rear deck, having first marked to bracket for alignment. It is possible with the deck in place, but a hell of a lot easier with it off. Stick the car on axle stands and let it cool down. While the car was cooling down we had a look around for things to do and found that the body-filler neck grommet was in very bad shape - we replaced it.
Protect the rear bodywork from scratches ! Once the engine is cool enough, remove the cambelt covers (10mm socket) and front cam cover bolts (13mm)
From underneath, remove the crank sensor (10mm) from its plinth. Turn the crank using a 24mm socket/extension on the front TV damper bolt (clockwise !), until the crank locking tool can engage on the 10deg BTDC #2 reference vane. Sometime this vane is marked white and the TV damper usually has a reference marking on it.
From above, view the front cam bearing caps looking for the camshaft drilling that indicate the firing stroke on #2 reference cylinder.
If visible, attempt to screw the cam tolerance pin into each of the front caps. If this is not possible, then the cam timing is not correct and you need to adjust your cam timing.....
If not visible, dive below and rotate the crank through 360deg to align with the firing stroke on #2 and try again.
Once the tolerance pins have confirmed that the cam/crank position and timing is correct, you must remove the pins :rolleyes: We were deep in instruction mode and forgot to take a picture..... here is one from the Library. From underneath, attach a timing pointer to a convenient sump bolt and fix your timing disc to the front of the TV damper.
Remove the crank locking tool and rotate the crank to 80deg ATDC, which corresponds to the tensioning point for the LH belt. Leap up and using your trusty Clavis gauge, take the frequency measurement in close to centre of the belt run - okay for an in service belt.
Dive under the car and rotate the crank to 120deg ATDC for the RH belt and take the measurement......We were again okay, but if you need to adjust the tension - using a 13mm spanner, free off the tensioner bolt while holding in postition with your tensioning tool. Reduce or increase the tensioning and tighten (Torque to 20Nm). Rotate the crank twice for the adjustment be recognised and take the measuerment again.
It is sensible to rotate the crank to the original reference position and once again check the timing with the tolerance pins. Once completed, replace the cam cover bolts being careful not to over tighten and strip the cam cap threads.
Finally replace the belt covers, remove the timing disc and replace the crank sensor and connector.
Finally, we replaced the rear deck which gives me a chance to post the most amusing image. Here is Gipsy trying to attach the aerial...... he´s a big bloke :respect: couple of hours to do.
A great guide to show you how to do this job and keep your V8 engine in top condition. Thanks to Mike for taking the time to put this together and help out other V8 owners.
We have been contacted by Lotus Cars to inform us that the procedure has been updated in a service bulletin. They have kindly supplied this to us to add to this guide. So please read the bulletin below before starting.
This mod was performed by Mike S on Gipsy's Esprit V8-SE
If you have any comments, feel free to e-mail me with at firstname.lastname@example.org