Technical Information (MGB 23)

MGB/MGA Rocker Arm Assembly Installation

Last Modified - 3/28/00

If you look closely at the MGB/MGA OEM complete rocker arm assembly, as fitted to the engine, you will notice that several of the rocker arms do not line up centrally over their respective valve stem center lines.

If you are installing the British Automotive supplied roller rocker kit, you can improve this situation as follows:

Machine your existing rocker shaft support pedestals (4) by removing 0.025" from both sides of each pedestal.

Assemble the rocker shaft and roller rockers in the normal manner then, without the pushrods installed, install the assembly to the cylinder head.

Torque cylinder head nuts to 25ft./lbs. and the rocker pedestal nuts to 15ft./lbs.

Centralize the rocker arms over their respective valve stems and calculate how many 0.025" shims will be required to accomplish this. Not all of the rocker arms will need shimming. No other shim sizes are provided, so, get the rocker arms as central as possible.

*Number your rocker arms and rocker pedestals. Remove the assembly from the cylinder head, dismantle, and install the shims that you calculated above.

Install the pushrods and rocker assembly in the normal manner. Torque cylinder head and rocker pedestal nuts per your workshop manual.

*To reduce friction and potential rocker arm "wander" over the valve stem, we also recommend the following:

When installing the 0.025" shims, leave out the 3 wire springs. Install the assembly as outlined earlier (pushrods still removed).

Using a caliper dial gauge, measure, the distance (3) between the rocker arms (these spaces were previously occupied by the wire springs). Subtract 0.020" from each of these measurements and record.

Machine the supplied aluminum bar to these recorded measurements.

Remove and dismantle the assembly and install these 3 spacers. Make sure that the outer spacers are in their correct location and that the rocker arms, and rocker pedestals, are fitted in the correct sequence.

Install the pushrods and rocker assembly in the normal manner. Check all pushrods for interference within their guide bores and also the vertical angle of the number 1 pushrod (when viewed from the side). Shims may have to be moved from the inside of the the rocker arm to the outside Torque cylinder head and rocker pedestal nuts per your workshop manual. As you torque down, be sure that the 3 spacer tubes are free to rotate. Tap the pedestals to prevent this as you tighten.

We supply 16 0.025" spacer shims as part of the roller rocker kit, which, should be more than sufficient.

If you are using 5/16" chrome moly tubing pushrods be aware that pushrod interference is more of a problem. In the engine rebuilding process we enlarge the guide tube holes to .660".