Notes on Big Seven maintenance etc.

Valve timing - to set and check

From new, Austin Big Seven engines do not have any form of timing marks on either the crankshaft or camshaft sprockets, that would enable valve timing to be reset when fitting a new timing chain to the engine. This procedure of setting valve timing is better done with all pistons, con-rods and crankshaft assembled but without the valve springs and collets assembled, just the valves inserted in the guides. Although, if necessary, it is possible to be done with valves and springs assembled.

Method
1) Set the tappet clearance to 0.004" - 0.006" on both valves in No 1 cylinder (inlet and exhaust), and do the same for the valves on No 4 cylinder. The setting to be done with the cam lobe on its base, ie No 1 valve fully open - set clearance on No 8 valve. No 2 valve fully open - set clearance on No 7 valve (this is known as datum 9) 1 + 8 = 9, 2 + 7 = 9, this can then be used for all valves - as long as they add up to 9, ( 4 & 5) (5 & 4) etc.

2) Before fitting the timing chain rotate crankshaft until both No 1 and No 4 cylinder pistons are at TDC (Top Dead Centre - at the top of the bore).

3) Now rotate the camshaft so that both valves on No 1 cylinder are fully closed and tappet clearance as previously set - check the position of the valves on No 4 cylinder, these should both be slightly open - ie no tappet clearance. The inlet valve should be beginning to open and the exhaust valve just nearly closed (this is known as valve overlap).

4) Without letting the crank or or the camshaft turn, fit the timing chain. With chain connected, rotate the crankshaft 720⁰, as the pistons come up to TDC, observe the valve position, these must be as in (3) above - that is, both valves on No 4 cylinder slightly open and both valves on No 1 cylinder fully closed with tappet clearance. In this position No 1 cylinder spark has just occurred.

From: Austin Big Seven Newsletter Nov 2007, by Robin Taylor (Austin big Seven Registrar).