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

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

Bespoke Crankshafts

Replacing an original crankshaft


Although the AC crankshaft is not the frail, failure-prone item that some would have us believe, supplies of good, original shafts are finite and for those wishing to replace their original AC crankshafts, whether for reasons of wear or higher performance, we can  supply bespoke, billet steel crankshafts and matching rod sets.  The crankshafts are made to our specifications by a leading company in this field and may be ordered to suit Vintage, PVT UMB, post-war UMB, UMC and CL engines.

The crankshafts are designed to offer far greater strength than the original items and also have much stiffer, having shorter big-end journals than the original shafts.

Your block will require slight modification to accept the crank and substitute bearings, which we can undertake on your behalf.  

The crankshafts are designed to accept our modern one-piece oil seal conversion and require one of our bespoke flywheels (which, unlike some of our competitors' flywheels, come complete with starter ring gear).  Front dampers are used with bespoke cranks although the early, damper type flywheel can be used via a special adaptor plate.  Normal AC clutches are used, either in standard or heavy duty form.

Bespoke cranks are made to order and delivery times can vary so early ordering is recommended.



Bespoke Conrods

Replacements for original conrods

Crankshaft Adaptors

New life for original crankshafts

Use of these new adaptors has enabled a number of crankshafts to be retrieved that, although sound in other respects, might otherwise have had to be scrapped through faults in their original adaptors, such as damaged or ground out bearing journals or rusted or broken sprocket teeth.  We have encountered several crankshafts on which a worn out No 5 bearing journal - the one that carries the load of the flywheel - has been built up by metal spraying that has subsequently developed cracks and splits or has become detached completely, leaving it free to rotate upon the crankshaft.

Traditional Type

The traditional type is a direct replacement for the original adaptor but with the advantage that it has no oil flinger or scroll, making it ready to receive a modern oil seal without further modification.  The block and sump will require modification to accept the carrier for the oil seal.  

Hub Type

The hub type of adaptor offers the same advantages as the traditional type but with the added bonus that having no flange allows oil seals to be changed without having to strip the engine first.  A bespoke flywheel is required with this type of hub, allowing the possibility of considerable weight reduction.

The bespoke conrods referred to above are most usually supplied with a steel crankshaft but may also be ordered for use with a standard AC crank in an engine with raised performance.  

Each rod is supplied with a new small end bush to suit the AC gudgeon pin dimension and is notched to accept the shell big-end bearings.  AC crankshafts must be ground to suit the sizes of the bearing shells.

Bespoke rods are made to order and delivery normally takes several weeks.

Bespoke conrod


Hub type


Bespoke Flywheels

Starter Ring Gear

Flywheels for all occasions

Our range of bespoke flywheels caters for a variety of applications, whether for fitting to one of our new steel crankshafts or to an original crank.  


Bespoke flywheels cannot be used with crankshafts originally mated to damper flywheels unless the crank is modified  to accept a front damper.

Although we normally keep some flywheels in stock, they are usually made to order according to the customer's requirements. 

Flywheels can be made to whatever weight is required, whether 20lbs (as per the later AC flywheels) standard or much lighter.  

New life for original flywheels

Many is the AC flywheel that has been scrapped because its ring gear was worn out, often with the teeth all but completely missing in one or more places.  This has usually meant robbing the best used flywheel available from another engine.

Now however, we can supply new starter rings to fit your original flywheel.  The old ring must be turned off the flywheel and the new one shrunk on and dowelled into place.  We would be pleased to undertake this work on your behalf if required.


 PVT Crankshaft End Float Control

Crankshaft Lock-washers

Flywheel Bolts

It can be quite difficult to set the end float in a PVT crankshaft, especially when the components are worn.  The task can become much easier and the results better using the new components shown above.  The aluminium ring is designed to take a modern oil seal instead of the old felt seal.  Please note that the seal runs on the hub of the crank pulley, which must be in good condition for the seal to work effectively.

These lock-washers are essential to prevent (top) the rear of the crankshaft from working loose and (bottom) to keep the front damper secure on a late UMB or a CL crankshaft.  All too often they are rusty and broken or missing al together.

Flywheel bolts are some of the most abused and neglected items on an AC engine, often being re-used until the threads have stretched beyond the point when the bolt can be said to be holding the flywheel securely in place.


Vintage Flywheels and Clutches

No longer the poor relation

For a good many years the Vintage AC and its engine, with its unique characteristics, have been largely ignored and spare parts have been very hard to find.  Often it has simply been a case of finding a less well used part.  This situation is now changing, values of vintage ACs are rising and we are introducing a widening range of parts for their hitherto somewhat neglected engines.

Getting to grips....

The picture at the left shows a newly made, lightweight flywheel for a bespoke vintage crankshaft while at the right is a relined vintage clutch fitted with one of our new steel clutch plates.  The relining and plates are suitable for either the engine-mounted or chassis-mounted vintage clutches.


Crankshaft Dampers

Crankshaft Pulleys

Damper rings

The rubber rings provide the damping effect in the early, damper type flywheel.  They are also among the most ignored components of the AC engine, the rubber often being degraded by contamination with with leaking engine oil and the damping effect seriously diminished, to the detriment of the balance of the engine.  Some crankshaft breakages can probably be attributed to this.  When rebuilding an engine it is essential to fit new rubbers to the flywheel.

Front dampers

The rubber bonding of the original Metalastik dampers is prone to disintegration through age and oil contamination, which means that the damper is no longer doing its job of absorbing crankshaft vibrations.  Our new crankshaft dampers are designed as replacements for the original items.

Important Note:  Front dampers were only fitted to the later UMB and the CL crankshafts, which were specially strengthened at the front end to accept the damper.  Front dampers should not be fitted to the earlier UMB crankshafts as there is a high risk of the threaded spigot at the front of the crank breaking off.  Early cranks can however, be modified to accept a front damper and we can quote for this.

Ace/Aceca dynamo pulleys

We have often found the aluminium pulley used to drive the dynamo belt on some Aces and Acecas to be in very poor condition, whether through wear of the Vee, breakage or corrosion, the latter perhaps deriving from winter salt on the roads.

Our new replacement pulleys are normally made to order but we may occasionally have some in stock.

Fan pulley

The fan pulley is another long-lived but much ignored item that eventually wears out until it will no longer drive the fan belt as the Vee becomes misshapen through overuse.  All too often, the belt is over-tightened to prevent slippage but this simply increases the wear rate and stresses the water pump bearings.  And when the belt begins to slip, it is no longer driving the water pump efficiently.

Normally made to order, we may have one or two in stock.


Clutch Assemblies

Engine Gear Sets

A new, exchange clutch assembly should certainly be fitted at engine overhaul, especially if the original friction plate is soaked in oil.  Freedom from slipping and juddering can transform the feel of a car.  The pressure plate should be balanced with the crankshaft and flywheel.

Usually supplied with bespoke crankshafts, a replacement gear set removes the slop and backlash in the drive to the distributor and makes accurate setting of the ignition much easier.


Cross-Shaft Shrouds

Timing Chains and Tensioners

Timing Sprocket Support Bracket

The cross-shaft shroud frequently becomes damaged over the years, usually through being left in place in the block during attempts to remove the rear cylinder liner.  We have seen many smashed beyond further use.

Our new cross-shaft shroud solves this problem and restores one of the shroud's main functions, which is to prevent excess oil from being flung up into the rear cylinder.  Its design also lessens some of the frailties of the original design.

We can also supply complete cross-shaft assemblies i.e. with new shroud, shaft, spring, bearing, nuts and washers.

The timing chain is a vital  component in any engine and especially so in an AC engine where its considerable length means that excess wear can cause the chain to slap against the inside of the chain case and can allow the chain to jump the teeth of the crankshaft sprocket.  A worn chain and a weak tensioner can jeopardise valve timing by falling to keep the camshaft in its correct relationship with the crankshaft.  Chain and tensioner should always be renewed during  engine overhauls.

The support bracket in the post-war engines was a nasty affair pressed from thin, easily bent aluminium whereas the pre-war version was a nice, solid bronze or aluminium casting.

Our replacement for the post-war item is machined from solid and will not bend, enabling the timing sprocket to be slipped off the camshaft and properly supported until replaced.



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