MED 998 ROLLER ROCKER SET

The assembly is a direct replacement on small-bore A-Series engines, but no, the shaft itself is a larger diameter for increased strength. We have also enlarged the rocker arm adjusters for heavy duty performance usage and reliability. All round, these are much stronger than standard rocker assemblies.

We've found that our 1.3:1 rockers give plentiful valve lift for all stages of tune on the small-bore A-Series. There is a limit to how much gas flow is possible with any engine/cylinder head setup, and increasing valve lift beyond what's usable by the engine will offer no benefits. 1.5:1 rockers are better suited to 1275-based engines, which can more effectively make use of the extra lift.

MED rockers are all roller-tip rather than full roller rockers, as we have found this gives the best longevity and accuracy. We run the 7075 aluminium rocker arms direct on the shaft, taking advantage of its larger diameter to spread the load. This is preferable to running needle roller bearings within the arms, from our experience.

Not all A-Series roller rocker assemblies are created equal, and we have gone to great lengths to ensure these are the most durable setup possible, whether it's for a long-distance road trip Mini or full-race car. Take the roller tips as an example, which feature a unique three-way retention technique at the roller pins. The 7075 aluminium arms have a higher tensile strength than many grades of steel, while the enlarged adjuster screw threads are there for ultimate longevity.

These suit all small-bore cylinder heads, so 848-1098cc engines. If you're lucky enough to have a 970 Cooper S or 1071 S, look instead at the 1275 rockers, as these have the same valve spacing as the larger 1275 engines.

Be wary of clearance between the rocker arms and the spacers, and also the rocker post stud nuts and the arms. We assemble the rocker shaft spacers to try and give the correct end float for most cylinder heads, but you can find variety here in the castings. If the arms are too tight against the spacers, firstly loosen the stud nuts and there will be some lateral movement of the posts, which often fixes it. In rare cases you may need to turn down the spacers a small amount to give more clearance (suggest around 0.005-0.010"). Check that the rocker post stud nuts/washers do not overhang the posts and contact the arms. If so, consider using an ARP head set, or machine down the fixings for clearance.

Yes these should fit inside a standard steel/tin rocker cover. For thicker-walled aluminium rocker covers, you will need to machine the inside rear edges for clearance, or perhaps take a look at the MED rocker covers, which come machined internally.

Yes it might be a good idea to order a set or two to experiment with. When the cylinder head or block have been machined, the valve seats re-cut, or a combination of all three, it can all affect the rocker geometry on an A-Series engine. The aim should be to achieve the correct valve lift of the camshaft at full lift, roughly indicated by the roller tips sitting centrally (fore and aft) on the valve tip at half lift. If the rocker geometry is incorrect, you will not achieve the desired 1.3:1 ratio between the cam and valve lift figures. Winding the adjusters out to their extremes may also give clearance issues with the pushrods.

We always recommend changing the head gasket when removing the rocker assembly, as you may end up disturbing the gasket while loosening off the rear stud nuts. Arm clearance can sometimes be an issue when using the standard head studs and nuts, so an upgrade to ARP head studs and nuts is a good plan.