Tappet Adjustment – Finding the Tipping Point

One of my earliest motoring memories was watching a mechanic adjust the 16 tappets of a 1940’s era Buick straight 8. This was a time when the hydraulic self-adjusting tappet was something in science fiction and the ability to adjust tappets while the engine was hot and running was the benchmark of a skilled mechanic. I might add it is a skill that I have never been able to emulate and having once tried it with the MG, I can assure you that it is not practical as the resulting oil spray covers everything.

In the Buick instance, the mechanic took about 20 minutes to complete the task, though high oil pressure was not a feature of this era. Today, the mechanic’s tappet adjusting skills have largely been displaced by the hydraulic valve lifter and ‘technicians’.

I recently had cause to adjust XPAG tappets. Unlike the Buick, the XPAG procedure requires a hot engine and the rotating of the crankshaft manually to access the tappet gap of an identified valve, against the fully open position (the tipping point) of an identified valve rocker. The same adjusting procedure is also applied cold to MGA/B series tappets.

Of itself, the described procedure is simple, but age has a way making ‘the simple’ a struggle when it involves arthritic hands, eyes that have seen better days, a front pulley dog nut on which a tab locking washer interferes with the spanner fit and observing when the identified valve rocker has reached its maximum opening – the ‘tipping point’.

Considering the problem, I found a simple solution.  As the accompanying photo shows, an open ended/ring spanner placed over the tappet rocker adjusting lock nut of the valve being opened, gives an exaggerated view of the valve rocker/valve movement and the picking of that elusive fully open ‘tipping point’.

Geoff Piddington #1319, Canberra, Australia.

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