Lotus 912 2175cc Engine (Not H.C.)
(article submitted by Ben Watson)
This is what can happen when the timing goes. The timing belt on this occasion did not fail, but the tensioner slipped from its pivot and knocked the timing out.
As a result there was no compression on cylinders 1 and 2 and about half what there should be on 3 and 4. The time had come to take the head off and find out exactly how bad the damage was.
Engine showing crank pulleys and tensioner.
Most people recommend removing the engine for this sort of work, and I have to agree, however if you don't have access to a hoist this can prove tricky, and if all you want to take off is the head there is an easier way! When working on the head make sure the engine is stone cold otherwise a few bent valves will be the least of your worries. There are some horror stores which go about when something like this happens. One Lotus dealer, who shall remain nameless suggested that the pistons would be cracked, conrods bent and liners warped. Unless you have been doing silly RPM when the timing fails your troubles should be limited to bent valves and possible damaged guides. Its always a good idea to replace the guides anyway. So back to the head. Before you start in ernest, make sure you remove the bonnet. Access can be difficult enough without making things worse!
1) Slacken off and remove the ancillary belts. I have no air-con which made life a little easier.
2) Drain the coolant and disconnect all the hoses to the block and head.
3) Drain the oil.
4) Remove the air box. (should be 10mm, the nuts inside the airbox can be tricky as they may be obscured by the carb intakes.)
5) Remove the carbs. Some would suggest that it is better to remove the inlet manifold with the carbs intact, however I found access to be difficult so I left the inlet manifold on. Be careful not to lose the O-rings which have a tendency to stick to the carbs when you remove them from the manifold.
6) Remove the HT leads and tie them clear of the head.
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Updated 21 Jul 2006