AC-6 - the website for all owners and enthusiasts of the AC two litre, six cylinder engine




What is an AC Engine?

Engine  Rebuilds

Blocks, Studs & Water Jackets

Spare Parts List One - Attaching Parts, Seals & Gaskets

Spare Parts List Two - Crankshaft & Cross-shaft Assemblies and Chains

Spare Parts List Three - Pistons & Liners

Spare Parts List Four - Sump Assembly

Spare Parts List Five - Cylinder Head Assembly

Spare Parts List Six - Ignition, 

Spare Parts List Seven - Water Pumps

Engines for Sale and Used Parts

Parts List

Cracked and Corroded Blocks, Studs & Water Jackets...... 

What a load of rot!


Facing the worst

The picture on the right shows an all too familiar sight - an AC cylinder block, in this case a PVT one, just about rotted out.  And even this is not the worst that we have seen!

How do they get in this state?

The rot is caused by electrolytic action which attacks both cylinder block and head studs.  Specifically, as the block deteriorates, the top surface of the block is rotted away making it impossible for the head gasket to seal.  This allows water to climb up the head studs and to emerge on top of the head, from where it drops down the chain case into the sump.  The sealing surfaces of the cylinder lands are also degraded and water enters the sump past the liners, turning the oil to a horrible, grey sludge.  The second picture shows a seriously corroded cylinder head stud.  Studs in this condition, as in the picture to the right, frequently snap. 

Starting at the beginning

It is a complete waste of time rebuilding an AC engine unless the cylinder block is in really good condition, meaning that there is no corrosion present and that all mating surfaces are both uncorroded and flat.  If this is not the case, then remedial action must be taken to avoid serious and expensive disappointment. 

Putting it right

Fortunately, a corroded block does not have to be scrapped.  Even very dire blocks can be retrieved cost-effectively.  Our water jacket conversions not only replace rotted material with sound metal but  restore the mating surfaces to ensure that the figure-of-eight gaskets and head gasket can perform their functions efficiently once more.

And when it's done?

When the water jacket replacement is complete, your block can be returned you for rebuilding, or we can complete the engine rebuild for you.

A badly rotted PVT block

Cylinder head stud ready to snap

Water Jacket Replacement

(1)  Removing the rot

The first step in any water jacket replacement is to remove the corroded water jacket and old head studs and to fit thread inserts for the new head studs where required.  

(2)  Machining it flat

The next stage is to machine the mating surfaces of the block and water jacket casting to ensure a perfect fit.  Once the jacket has been fitted, its top surface and cylinder lands are machined to the correct height, following which the new housings for the cylinder liners are matched to the originals.  

3)  Fitting it out

When the two parts of the restored block have been sealed and secured together, the final tasks are to drill and tap the holes where studs will be fitted and to install the new feed pipe that carries oil from the main supply up to the camshaft and rocker gear.  The block and sump may also be machined now if an oil seal conversion is required.

Once the machining is finished, the cosmetic work can begin, the two parts of the conversion being blended together so that the join becomes virtually undetectable, as shown in the photograph below.  Please note that no digital re-touching has been employed to disguise the join.

Following completion of the first stage of the cosmetic work, the restored block is pressure washed to remove remaining swarf and aluminium dust.  Final cleaning and touches to the appearance of the block are carried out when other mechanical work is complete and the engine is ready for assembly.  The rebuild of the engine shown on the right is about to commence following its water jacket replacement.  The smooth-as-glass top face of the block is clearly shown.   

Over the years we have progressively developed our block restoration techniques so that blocks that even we might once have dismissed as beyond hope can now be salvaged and restored to healthy life.

The pictures below show one such block.

If you have a block that you think is a hopeless case, give us a call - we may just have good news for you.

A Proven, Cost-Effective Technique

How proven?

Although we cannot take the credit for inventing water jacket replacement, we can claim to have developed and refined the technique to a high degree of reliability, attested to by the numbers of converted engines providing dependable service to their owners.

In addition to enabling the mechanical function of an engine to be restored, the appearance of the converted blocks, with their near-invisible join, is such that they are frequently mistaken for new ones.......high praise indeed!

Why Cost-Effective?

The current cost of a complete water jacket replacement is from 2,000.00.  For this your engine, whether vintage, PVT or post-war, will look as pristine as the one above, with new water jacket with an almost invisible join, new head studs and all other studs fitted and/or replaced as necessary, plus a new timing chain tensioner and HT clips ready fitted.  The water jacket conversion is by far the most cost-effective way to restore a corroded block to reliable service.  But why?

In order to appreciate the cost-effectiveness of our block conversions, one must examine the alternatives:

1)  Repair of corroded block without a new water jacket

Some blocks can indeed be repaired without needing a new water jacket - it all depends on the degree of corrosion present.  Small amounts of welding are possible in the thicker sections of 



these blocks but should only be undertaken very sparingly and by a highly experienced welder.  Welding of extensive cracks in the thinner parts of the block, such as the sides, should be avoided as the cracks can spread all over the place and the block can distort badly.  Such welding is likely to be expensive.  Wrecking the block can make it more expensive still!  Cracks large and small can usually be dealt with successfully by stitching.

Small amounts of corrosion in the stud bosses may be corrected by trepanning around the stud and inserting a thick aluminium washer in the trepanned hole.  AC used to carry out this procedure - whilst at the same time trying to deny that their blocks suffered from corrosion!  

Cylinder head studs can be removed; sometimes but very rarely do they just unscrew but more likely a couple will come out and the rest will either refuse to move or will snap off where they enter the block.  Studs can be removed by using a succession of hollow drills to bore downwards around the stud.  The stud can usually then be unscrewed and the block repaired by inserting tubes around the studs to fill the drilled gap.  This is a slow, tedious and expensive process, the total cost of which often exceeds that of fitting a new water jacket, and one which still leaves corrosion in the block to be addressed.   Such may entail milling flat of the liner beds and top surface of the block; this can lead to serious dimensional problems at a later stage.  And more expense!

2)  New blocks

New cylinder blocks have been available for a little while now and this is a good thing.  However, they cost around 5,000 each without VAT and there will be further bills for line boring of the main bearing housings to suit your particular crankshaft.  There are in fact very few original blocks that cannot be retrieved, thereby saving large amounts of money and, importantly to some, the originality and provenance of your car.

Cracking of the Cylinder Block

Cracking and its causes

Cracking of the block is sometimes caused by frost or by mishandling - as in over-excitement at the throttle causing the engine to blow up and the whizzy-round bits to come out through the side - but there is another, not widely acknowledged cause and that is flexing of the chassis.  

This phenomenon occurs mostly in pre-war carsQuite simply, the chassis bends and the engine, effectively bolted almost solidly onto it via its almost completely ineffective mounting rubbers, tries to bend too but being a rigid casting it cannot bend so it cracks instead.  AC were well aware of this problem and in the late thirties revised their engine mountings.  Even so, the revised version was less than perfect and by now the rubber mountings have become flattened out, oil sodden and inflexible lumps that can no longer perform their function.  Engine mounting rubbers cannot be ignored, should be inspected at least whenever the engine is removed and if possible they should be upgraded as well.  

A stitch in time

The picture shows a block that has been cracked by flexing of the chassis.  A repair had been attempted by welding up the crack on the inside of the block.  The weld has now been removed and the crack repaired properly by stitching, which can effect a highly secure repair that can be made virtually invisible.

The stitching technique can also be used to repair cracks and breakages caused by frost or accidental damage; even when whole chunks of block have been dislodged by conrod or crankshaft breakage.


A badly cracked PVT block

This block was repaired, the crack successfully stitched and a new water jacket fitted.

The pictures above show just a few of the thirty or so water jacket conversions that we have carried out.


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