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 Four - Sump Assembly......

AC post-war UMB bare sump after chemical cleaning and rear crank oil seal conversion

More than just somewhere to keep a dipstick

The sump of the AC engine is not there just to hold oil - it also contains parts i.e. oil filter, oil pump, oil pressure relief valve whose correct functioning is vital to the well-being of the engine.  It also provides the housing for the starter motor.  

It is worth noting that not all AC sumps are the same; some of the main differences are:

  • The Vintage sump has the oilways for the main bearings cast into the bottom of the sump rather than the separate tubing header used in the later engines, the oil filler is situated of the left hand side of the sump instead of on the rocker cover as in the post-vintage engines while the starter motor is mounted much lower down than on later engines.

  • The PVT sump is deeper that the post-war sumps and is the same depth along its length, lacking the step-up of the later sumps.

  • The later CL sumps had a central oil pick-up to prevent oil surge and pressure drop on braking and right hand bends.

  • The semi-circular opening at the rear differed in design according to the type of oil seal used.

Although sumps can be swapped around to different engines, there will nearly always be some fettling required as they were originally pair-matched to their respective blocks and non-compatibilities will arise, especially in regard to the rear oil sealing arrangements, which also affects certain sump and crankshaft combinations.   Our oil seal conversion overcomes this problem as the differences are machined away.

Just like the components of the block and cylinder head, the working parts of the sump can wear and eventually fail.  And we can provide improved spares to replace then all. 



Oil Pumps and Drive Shafts

Post-war oil pump, upgraded

This our top-of-the-range post-war pump and is a favourite for use in competition.  The pump body is machined from solid bronze and is fitted with finely meshed helical gears whose shafts are carried at each end in large diameter bearings.  This is a serious pump for the discerning enthusiast.

If this pump is intended for use in a sump originally fitted with a short length AC pump, one our extended cover plates will be required.

Post-war oil pump, traditional

The Traditional model is a popular choice for many post-war models.  The pump is closely styled upon the original AC pump, has a cast bronze body and, like the upgraded model, has gear shafts with double bearings.

If this pump is intended for use in a sump originally fitted with a short length AC pump, one our extended cover plates will be required.

PVT pump

The long gears and double bearings that have made our post-war pumps so successful are also available for the narrower diameter pump from the pre-war engine.

These pumps are only made to order, an extended cap is sometimes fitted and, owing to wide variations in the sumps, we require your sump when the pump is made to ensure correct fitting.  

Oil pump drive shafts

A new drive shaft should be fitted whenever a new pump is installed and whenever an engine is rebuilt as the slotted end that engages the pump is nearly always very worn.   Please quote engine year, type and shaft length when ordering as lengths differed over the years. 


Oil Pressure Relief Valves

New design relief valves

Relief valves and springs

Oil pressure relief valves are a much ignored engine component, especially in the post-war engines as the original AC valve cannot be extracted from the engine without prior removal of the sump and then only with difficulty without special tools.  

Relief valves often leak and lose oil pressure through bad seating of the ball or plunger and through a weakened spring.  While old valves can be restored with our new balls and springs, we can also supply completely new valves for both PVT and post-war engines.  

These have the great advantage that they can be removed from the post-war engine with the sump in situ. 

Relief valve spring


Filters and Plumbing

Filters - ending a nightmare

The original AC oil filter is not very efficient and is difficult and messy to change.  While the Aces and Acecas had remote filters - we stock the elements - any AC can be converted to a remote installation with a modern, spin on canister filter.  Oil changes become much easier and cleaner and the need to remove side mounted dynamos to gain access to the filter housing is banished forever.

Filters can be mounted wherever most convenient and we can supply all the headers, pipes, clips and a wide variety of rigid and swivel unions in various sizes.

Example of typical remote filter layout (temp. picture)

New oil pipes for the CL engine



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