Technical Information (MGB 26A)

Tubular Pushrod Interference Information

Last modified - 04/15/06

PART A
When using Harland Sharp roller rocker assemblies in conjunction with tubular pushrods, it is important that the pushrod cup does not contact the roller rocker body at full valve lift. Damage to the rocker arm will occur if this is allowed to happen.

In technical articles MGB16, MGB24, and MGB26 we have discussed at the length the complexity of the variances in valve train geometry. If you have not already done so, I suggest that you read these for a better understanding.

Along with the Harland Sharp 1.55:1 roller rocker kit that we have supplied you, we have enclosed 8 lightweight valve springs to pre-assemble to your exhaust and intake valves. Adopting this method of approach has several advantages, these are as follows:

1. Allows the cylinder head gasket to be eliminated before the final assembled cylinder head is installed to the engine block.
2. Allows the installer to simply finger tighten and untighten cylinder head and rocker shaft/assembly hardware.
3. Upon full valve lift, allows for simpler pushrod cup end to rocker arm interference checks.
4. Allows for easier shim placement for centering rocker roller tips over the valve stem ends. Twelve .025” shims are provided for this.
5. Allows for easier spacing measurements between the rocker arms. These measurements are then used for machining the aluminum spacers (3).

Since, you will be using your original rocker pedestals, we highly recommend that they are machined .025” on both sides of the pedestal before carrying out the above.

NOTE: It is extremely important that aluminum spacers are used between the rocker arms. Simply retaining the OEM spring spacers is unacceptable. Ignoring this advice will lead to the hardened steel roller wearing into the roller aluminum supports.

PART B
Be sure to check for pushrod to pushrod guide hole contact in the cylinder head. If pushrod contact is being made, elongation of this hole should be carried out.

Pushrod contact should be checked at valve closed, valve full lift and back to the valve closed again cycle.

Excessive elongation of these cylinder head guide holes should be avoided. This is especially true with aluminum cylinder heads, where break through into the coolant passage may occur.