This blog, in addition to the usual maintenance details for classic mini cars, an attempt is made to explain the "whys" and "wherefores" of the various jobs.

Saturday, 17 October 2009

A New Lease of I -if for Your Engine

One firm that has made a special study of the cll'ectivcness of reconditioning small modern engines in this manner is CJ.M.A. Reconsets Ltd., 119 Uxbridge Road, London, W.12. As ■ K'MIII ol their experience, they supply a standard reconditioning kit which Includes new pistons, fitted with special oil-control rings (norm¬ally rendering reboring unnecessary), a set of connecting-rod bearing ihelU, MW exhaust valves and a complete set of valve springs, a timing chain, I complete set of gaskets, gasket cement, and graphite assembly compound.

In deciding whether a partial overhaul will be satisfactory, the condition of the crankshaft is likely to be more important than the amount of wear on the cylinder bores. Excessive connecting-rod bearing clearances can result in more oil reaching the bores than can be controlled even by new pistons and special oil-control rings. If the engine has covered more than 40,000 miles, therefore, it would be as well to enlist the aid of someone who can measure the crankpins with a micrometer If the wear exceeds 0-001 in., it is advisable to have the crankshaft re-ground. Even half a "thou" of wear can cause an appreciable increase in oil consumption.

Fitting new connecting-rod bearing shells is usually all that is required when a partial overhaul is undertaken at between 20,000-30,000 miles. In any event, the shells should be replaced as a matter of routine at this mileage.

The bearings are of the thin-shell type which can be installed without the need for skilled fitting. No shims are used and the caps should on no account be filed or rubbed down to take up excessive clearance. Provided that the crankpins are not scored or badly worn, the installation of new bearing shells will give the correct running clearance and restore normal oil pressure.

If" a prc-1961 Mini is to be overhauled, make sure that a self-lubricating Devi bush is fitted to the crankshaft primary gear. This is a simple and cheap modification which eliminates the previous tendency of oil to find its way into the clutch, causing the clutch drag which was one of the faults of the earlier Minis. Any B.M.C. dealer should be fully familiar with it.

The difficulty in carrying out the type of work just described lies, un¬fortunately, in the preliminary dismantling, as it is necessary to separate the upper half of the engine from the transmission casing in order to obtain access to the crankshaft and connecting-rod bearings. To do this the engine and front sub-frame must first be removed as an assembly. This calls for the use of a hoist by which the assembly, which weighs nearly 4 cwt, can be supported and the body subsequently raised at the front to clear the assembly, after the appropriate preliminary discon¬nexions and dismantling; the engine and sub-frame assembly can then be rolled forward on the front wheels, clear of the body.

The engine must then be freed from the sub-frame and lifted clear with the hoist. Removal of the clutch, flywheel, flywheel housing, and of the timing cover and gears will allow the engine to be parted from the trans¬mission case. It will also be necessary to remove the cylinder head if the pistons and piston rings are to be serviced, as these are withdrawn from the tops of the bores.

It will be seen that a considerable amount of dismantling is involved; moreover special service tools are required at some stages. In the circum¬stances anyone contemplating the work should consult his local B.L.M.C. dealer. It may be possible to borrow or hire the equipment needed, together with a workshop manual which is virtually essential if pitfalls in dismantling and reassembly are to be avoided.

It must be assumed, of course, that an owner who is prepared to tackle this type of work will have had some experience of engine dismantling, fitting and assembly or will be able to rely on the guidance of an experi¬enced mechanic. The do-it-yourself owner can also learn a lot of the essential "know-how" (which is not necessarily included in a workshop manual that is chiefly concerned with dismantling and reassembly) from a practical handbook such as Engine Repair for the Owner-Driver or Automobile Workshop Practice, which are published in Pitman's Auto-mobile Maintenance Series.