Engine Rebuilds

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Don’t despair if your classic’s engine needs overhauling as you may get away with this cheap fix that was a popular repair when your car was contemporary

For the average classic owner, overhauling an engine is a pretty major job in terms of labour and finance. However, you may get away with a good job for under a couple of hundred quid.

How? It’s called a ‘top and tail’ and the beauty of this halfway repair is that you may not even need to hoist the engine out to carry it out. Essentially, a top and tail is where you remove the cylinder head and sump and yank out the inners leaving the heavy block (with its crankshaft) in situ so there’s no need for a hoist and you can carry out the work in the garage or driveway with the minimum of tools and knowledge simply by relying on common sense and a manual.

This type of repair is as old as the hills and was very popular back in the 50s-70s. Indeed, dedicated overhaul kits costing around £25 comprising of new pistons bearings and gaskets etc to complete the job were widely marketed, tailored for engines that were showing signs of wear at around 50,000 miles but essentially in decent shape and not in need of a rebore or crank regrind.

You can still carry out such work yourself to achieve similar good results; the kits aren’t available anymore but you can still separately purchase new pistons and rings, crank shells (known better as ‘Big Ends’) and gaskets and quite cheaply too if you shop at autojumbles. So if you want to put the pep back into your classic, as well as save the unit from further wear and more expensive damage and need only normal tools plus a torque wrench, valve spring compressor, piston ring clamps and a spare couple of days, read on.

DROP ’EM!

The sump that is and this is where you’ll determine whether you can carry out the repair on your engine. That big old oil pan has to be removed to gain access to the crankshaft and pistons but it’s not straightforward on every classic due to it fouling the suspension, steering or chassis.

To enable sump removal, the engine usually needs to be raised after disconnecting the engine mountings and jacking the block up (taking care not to over do it and strain the gearbox) before slipping some wooden wedges between the engine and chassis mounts. Some engines don’t require any shifting which makes it much easier although on most you’ll still need to turn the engine over slightly so the crank is horizontal and so the journals don’t get in the way.

It’s not easy to generalise but the easiest sumps to remove are on older classics not fitted with rack and pinion steering which, usually along with a cross-member, fits in tandem with the sump.

This may scupper the whole idea although even on some cars where a steering rack is fitted it is sometimes possible to drop the sump and move it to one side to gain suitable room rather than completely withdraw it. It’s wise to check this for yourself first to see if it is at all possible but don’t refer to a workshop manual as it’s likely that it will not recommend such repair techniques – full stop; a case in point being Mk3-5 Cortinas where Ford insists that the engine has to come out – but it doesn’t (I’ve done it-ed).

If in doubt, speak to a marque specialist on any tricks of the trade but even on vehicles where it is indeed possible (and this includes many Jags, Fords, Vauxhalls, Rootes classics and Rover 2000s) you may need to remove some steering assemblies or even the entire front axle. It stands to reason that as you will be mainly working underneath, proper jacks and axle stands must be employed.

OBTAINING THE NEW ENGINE PARTS

As we said earlier, ready made kits used to be marketed (you may find one at autojumbles) but now you’ll need to purchase new parts individually and you can’t (or shouldn’t) do this before stripping the engine. The reason is quite simple – on an old classic it may well have been done before!

If the engine has been rebored and the crankshaft reground then ‘oversized’ rather than standard spec items will be needed. Most engineering shops will stamp a rebore size on the block’s face and you should find markings on the individual crank shells – failing this an engine shop will verify what sizes you need.

WHERE’S THE WEAR?

Hold your horses, before you even trot off to get your bits, check how bad the old parts are first. Are the cylinders too far gone for simply new rings to compensate – ditto the pistons? The best way of determining the former is to take an existing piston ring off and place it at the top of the bore and check the ring’s gap with a feeler gauge; do the same at mid point. Your manual should tell you the acceptable tolerances but usually 10-12 thou is the maximum new rings can compensate for before new pistons or a rebore is needed.

If the crankshaft’s journals (where the bearing shells reside) do a passing resemblance of a well worn 45 record like our picture shows, then only a stripdown and regrind will restore performance and oil pressure. If all is within spec then you have a few options: you can simply get away with new standard piston rings, fit special oil control ones such as ‘Cords’ which effectively also recut the bores or install new pistons and rings, depending upon their condition; again an engine shop can advise here.

Assuming that the ‘small’ ends are okay (these are opposite to the big ends and are located in the pistons – again an engine repairer can advise but their replacement is more involved) then a set of big ends takes care of the block although you can also renew the crank’s main bearings and it’s a wise move. While you can’t remove the crank in situ, you can replace the shells by removing the main bearing’s caps and sliding out the old and slotting in the new – fiddly but doable.

Bear in mind that you should ideally renew any of the crank bolts you disturb as they can stretch and break if reused. You should at the very least renew their locking tabs and torque down to their correct settings. While it’s so accessible, a wise owner should consider renewing the oil pump and certainly clean out the sump and oil strainer.

IT’S A FIT UP

To avoid confusion remove the pistons individually as they should go back in their respective cylinders. Before fitting new rings, clean up the pistons and the ring’s grooves, an old broken ring is ideal for this. Fitting new rings is straightforward but they may need gapping and remember to space them out otherwise you’ll get oil blow by.

While we know of inventive DIYers getting away with makeshift methods, a proper ring clamp which squeezes them in position as you pop the pistons back in their bores, saves the possibility of any breakages. If the ‘top end’ is in good order and the rings aren’t worn then it is possible to renew the ‘big end’ shells without removing the pistons by simply sliding them up the bore away from the crank journals and fishing out the old before slotting in the new. If you are doing this, fit the bolts back to the conrods as you may need to grip them with pliers to pull them back to fit on to the crankshaft.

It goes without saying that cleanliness and copious fresh oil is part and parcel of the rebuilding procedure. And always fit a fresh sump gasket or you’ll probably be dropping it again to cure an infuriating and messy leak!

TOP JOB

With the bottom end as good as new, it’s folly not to overhaul the cylinder head as it’s a cheap repair. Basically, it involves removing the values (use a proper compressor and take care with the valve’s collets) and scraping away the built up carbon deposits in the combustion chambers, valve necks and the head’s ports. The secret of putting all the power back is to lap in the valves (assuming they are in good order, not damaged or burnt) thoroughly using grinding paste and a simple wooden grinding tool. It really is a ‘grind’ to achieve a uniform surface on the head and valve seats but essential. Or you can be lazy and have an engineering shop do it along with installing unleaded seats which is really a bit of a no brainer if you are keeping the vehicle long term.

Typical cost is around £150-£200 but if you retain the existing ones, fit new valve springs and valve oil seals, both of which will be worn.

ALMOST THERE

Reassembly is the reversal of dismantling, ensuring items such as bearing caps go exactly back as before, although you’ll need to reset the valve clearances and, if overhead camshaft, fit a new belt. The engine will need running in, especially if you have fitted Cord rings, and after 500 miles re-torque the cylinder head and change the oil and its filter.

And that’s it, a weekend’s work means that you should see another 40,000 miles of peak performance from your classic and all for a couple of hundred pounds. Compare that to the price for a professional rebuild costing thousands and you’re laughing all the way to the bank.