Sunbeams are noted for wearing out cam chains , which is not surprising since the means of taking up any increase in tension as the engine heats up is to compress the very strong spring in the adjuster .
The system described below works on the same principle as hydraulic tappets , automatically maintaining zero clearence and constant tension at all times . It uses the original chain slipper and plunger whilst the new parts are all fitted from the outside of the engine .
There are four parts to make as shown below , also required is a light spring , one that is easily compressed between thumb and finger and which will fit inside the plunger . The reason for having the 0.040" hole in a separate plug is in case you break the drill , if you are brave you can drill directly into the end of the barrell .
The drilled BSPT plug is fitted into the barrel , the spring and plunger are loaded into the other end , then the barrel is screwed into the engine until all the slack in the cam chain is taken up . The barrel is then BACKED OUT one complete turn and locked with the nut . This backing out is to allow for any increase in tension as the engine heats up . The Dural cover may now be fitted and the oil supply ( Tee'd off from the oil pressure switch ) connected up .
Upon starting the engine the adjuster will click away merrily as the cyclic variation in chain tension forces the plunger in against the spring , when the plunger is pumped out to tension the chain the noise will cease and from there on the system is entirely automatic . The 0.040" drilling acting as a non-return valve to FAST increases in tension whilst allowing any SLOW increases to be relieved .
