Aston Martin DBSV8 1969 - 1972

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DBSV8 Workshop 2

Andy Chapman gives advice on tuning the FUEL INJECTION  page 2

Tappets & Valve Timing

The V8 fuel injection engine has a habit of ‘choking’ itself on warm up if the tappets have closed up and the valve timing has altered due to wear, i.e. if every other setting is correct. Most carburettor engines do not show up faults when the tappets and valve timing are not standard. Therefore it is quite important to get these settings correct so that a fuel injection engine will ‘‘breathe correctly”. These are as follows:

Valve timing inlet open .060” @ TDC. Tappet .009” to .010”

Valve timing exhaust open .050 at TDC. Tappet .010”io .011”

Engines which have covered 40,000 miles since any top end work ought to be looked at. Tappets close up, timing chains wear and if the tappets close too much then the back of the cams become damaged. This is my advice, especially if the car has been driven hard.

Faults: — ‘popping’ back through the air filters and some rough running. Twin contact distributors are a problem but OPUS ignition has overcome some of the problems. The base plates develop up and down play at point A, figure 2, and sideways play at point C. The rev-counter needle usually jumps when this fault is apparent with the engine idling. Remedial work can remove play at A -& C, but the important point is the plate must swivel freely with no play i.e. vacuum capsule or servo unit must be able to operate correctly. Replacement base plates, Lucas part numbers: Top plate number 54422584 and bottom plate number 54422617.

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