Performance

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At the heart of any thorough rebuild should be the engine. After all, what’s the point of having a lovely classic that doesn’t go like it should?

Some restorers make it a rule to test run the engine, or at least carry out a compression test before deciding on the next course of action, and this is wise, because if the unit is essentially sound, you may be opening up a can of worms by stripping a perfectly serviceable engine which either doesn’t need overhauling, or is difficult and costly to rebuild. A good policy is to check with a specialist or owners’ club to ascertain any known weak or wear spots on that power unit and the likely costs – and availability of the most common repairs.

A compression test tells you a lot. The readings should be uniform; if not carry out a ‘wet test’ by adding a few ccs of oil down each bore. If the readings improve, it points to suspect cylinder bores and pistons. If the bores are becoming slightly worn but still with tolerance, a set of Cords (or similar) rings, which effectively ‘cut’ a new bore (check if they are still available for your car) may save you the expense of a proper rebore.

If you can’t hear it running, carry out a static test; with the spark plugs removed, check how easy the unit turns over by hand and look for signs of any recent work carried out such as fresh gaskets, clean oil, and so on. However, if you suspect serious wear present then you’re simply wasting good money carrying out anything less than a full overhaul – which can be costly. Unless you wish to keep the original engine to preserve the ‘matching numbers’ on the log book (usually of most importance on a rare or expensive classic) an alternative is to find a good second-hand engine at a breakers or autojumble although you need to have a sound knowledge and how to check the unit for wear – or you could easily be buying another engine that’s equally as bad as the one you have!

Bore wear can be gauged both visually and by touch with the cylinder head off or if you’re only purchasing the ‘bottom’ half. If there’s undue scuffing then the rings have ‘picked up’. With a piston at the top of the block, can it be ‘rocked’ excessively, pointing to wear? If all is okay, simply fit new piston rings but check first whether you require ‘oversized’ ones due to the fact that the engine has already been previously rebored.

If you do intend to strip the unit and you find it’s in good order, it’s still daft to rebuild it without replacing straightforward items such as the main bearings, shells and piston rings; usually all low cost items, saving you the time and effort later on.

With the cylinder head off, also take the opportunity to not only decoke it but also have new valve guides and hardened valve seats installed enabling the engine to happily accept unleaded petrol in the future without any additives needed. At the very least, replace any suspect valves and lapping them in together with renewing the valve springs and oil seals, if fitted. If you can, have the head face lightly skimmed to remove any corrosion present (usually alloy types suffering here).

If you require another engine, it gives you the ideal opportunity to also upgrade at the same time, such as slotting in a 1600 where a 1.3-litre used to reside, for example or fit a tuned ready-to-go exchange unit.

How much life is left?

A case of heads you win

If you strip the engine, it’s illogical not to have the valve seats replaced with hardened types and a slight head skim so that you can use unleaded fuel with impunity. At the very least, decoke and fit new valve springs and oil seals

Best budget bhp boosts

You’ll find many classics are fitted with engines from a later model or a GT version to gain a cheap power increase as insurers are pretty relaxed about this. For example, 1275cc for a Midget/Minor and 1.3/1.5-litres for a Herald and Spitfire

Don’t ignore little things

During an overhaul, don’t overlook items such as the carbs and distributor as these significantly affect performance, economy and reliability yet are strangely overlooked or ignored. Although new carburettors can be expensive it’s still worth doing properly

Five top tips

Watch the costs

These can easily mount up so don’t underestimate the cost of proper rebuild, factoring in a rebore, crankshaft regrind, new valve seats and so on. Typically, the outlay will be in thousands if it’s a good quality overhaul, making a ready-to-go exchange unit more cost-effective

Watch wordplay

If you opt for an off-theshelf reconditioned engine watch the terminology in the adverts. There’s three states of quality available and you get what you pay for: Remanufactured, Reconditioned and Rebuilt. Remanufactured means the unit is returned as close to as new as possible, reconditioned usually points to where only worn parts are replaced or overhauled while rebuilt can imply that it was simply taken apart and rebuilt with new gaskets!

Enlist the feds

Word and mouth along with a good reputation go a long way as does rebuilders who are members of the Federation of Engine Remanufacturers (fer.co.uk)

Gearbox gripes

A metallic silvery taint suggests of a bearing failure, for example. If you can remove a ‘top plate’, turn the mainshaft and check the cogs for general wear and chipped/missing teeth. If the transmission comes with a gear lever, select all ratios. Do change all oils and if you have split the engine from the ’box, renew the clutch assembly. All you can do with an auto box is to check the fluid cleanliness; if it looks and smells burnt it could be overheating due to its bands slipping

Axle folly

If axle has half-shafts, feel for general wear and play. Check the axle’s CWP