” ……there will be a weeping and gnashing of teeth ” Matthew ch.25, v.30 ”
Lockdown brought the opportunity, long overdue, of recommissioning my spare TA14 engine. I had retained this because the block was only 20 thou oversize, no perceptible lip on the bores, and turning with the nice sort of stiffness that comes with fine tolerances rather than neglect.
But what’s this ? an unfamiliar clicking noise at the front end with each revolution. Nothing else for it…. off with the pulley and the timing cover. Curious !, nothing immediately obvious, but then I notice the timing marks are poles apart from the juxtaposition that George Lanchester had intended. Curiouser, attention turns to the tensioner, where I perceive that the tip of the pawl (C2961 in the parts supplement ) has broken off. Its tooth has descended into the chain (thankfully without damage), and the retaining spring is now resting on the ratchet, thereby causing the ‘ click’ Tension has become much reduced thus allowing the chain to slip, and the timing to become adrift. A telephone call to the ingenious Chris Prince produces a replacement pawl unit in next to no time, re-assembly takes place, and the proper rotation is resumed.
This experience is offered as a cautionary note to engine rebuilders as a point to check. The pawl unit does not receive any direct lubrication, but relies on splash from chain rotation, and can dry out with any lack of use.
HISTORICAL FOOTNOTE
As first designed in 1936, in 12/70 form, this engine was not equipped with a tensioner, and used a 66 link chain. an arrangement which continued up to TA14 engine 21849, after which the aforementioned tensioner, and a 72 link chain was fitted. Instances have occurred of earlier engines being retrospectively fitted, and indeed, ever curiouser, of later engines being converted back to the 66 link version.
It is possible to adjust, or replace the chain on 72 link engines without pulling the sprockets on
crankshaft and camshaft, but on 66 link engines this is not so.
Given that the engine number identifying plate is only split-pinned or pop-rivetted into position on the block, and can fall off, caution should be exercised in identifying what part fits which during major overhauls.
DAVE CULSHAW
Alvis Archive 