This kit contains parts and instructions for installing a conventional-style rear main seal on the 1275cc  A -series engine as fitted to the A-H Sprite and MG Midget and as used as an upgrade to the Morris Minor. The kit does not contain the sealing compound or gaskets necessary to re-install the engine back-plate and upper rear main extension piece.

Installation requires some minor machining of the engine back-plate and upper rear main extension piece. This work can be done on a drill press using standard tools.

The kit was designed for installation on the stock cast steel engine back-plate supporting the rib-case gearbox. Cars fitted with adapters to accomodate other gearboxes may require additional machining on these adapters to allow the seal mount to be installed. This will probably require the use of a milling machine to expose the surface of the original back-plate or to precisely remove material to provide clearance and proper spacing for the adapter.


Read all instructions before proceeding and identify kit parts.
Following the instructions contained in a good shop manual, remove the engine and gearbox from the car, detach the gearbox from the engine and remove the clutch and flywheel.

Remove the engine back-plate and clean thoroughly. Do not remove the upper rear main extension at this time!! Inspect the mating gasket for damage and replace as necessary.

Place the 3A0005 Seal Housing on the aft face of the plate and align the three upper 11/32 holes with the corresponding holes in the plate as shown in Figure 1. Temporarily securely attach the housing to the plate and, using the two lower holes in the housing as a guide, clamp the plate on a drill press and drill two 17/64 diameter holes through the plate.

Remove the clamp and the housing and enlarge the two lower holes in the plate to 11/32 diameter and de-burr. Thread the newly enlarged holes with a 5/16 tap all the way through and deburr as required.

Scribe around the upper rear main extension or otherwise index it so that this piece can be re-installed in EXACTLY the same position. This is EXTREMELY important!!

Remove the upper extension from the block. Inspect the thin paper gasket for damage snd replace if required. Thoroughly clean the extension, mating block and lower main bearing cap, being careful not to destroy the indexing marks you made when removing the extension.


Spotface or counterbore 9/16 diameter at the attaching points to reduce the thickness of the three mounting ears to 3/16 as shown in Figure 2. De-burr after machining.

Apply a very light coat of sealant (Gaskecinch is recommended) to the bearing cap mating surface of the upper extension. Position the upper extension on the block and align with the marks you made at removal. Secure to the block using the three button-head cap screws and toothed lockwashers. You may wish to use a Loc-tite product (Blue) in this application.

Reinstall the engine back-plate, omitting the bolts which will attach the seal housing.

Place the housing against the backplate and ensure that it is flush and not fouling the upper extension mounting screws. Relieve the housing locally for clearance if required.

Fill the gap between the backplate and the rear main cap extension with silicone sealant. It may be helpful to fit a packing between the plate and cap to prevent sealant running down.

Press the NF641 Seal into the housing with the open end toward the block and apply a light film of engine oil to the seal lip. Apply a thin coat of sealant (again, Gaskecinch is recommended) to the plate mating surface of the housing.

Slip the seal and carrier over the crankshaft boss and attach loosely to the block with the bolts and washers provided with the kit using the fine-threaded bolts in the upper three holes, and the coarse-threaded fasteners in the lower two.

Rotate the crankshaft six to eight times to center the seal, then progressively and evenly tighten the carrier attaching bolts in a criss-cross pattern to 150 in-lb.

Measure the depth of the recess in the back of the flywheel. If greater than 0.140 , place the 3A0006 Spacer in the recess and install the flywheel on the crankshaft.

Install the clutch, re-attach the gearbox and re-install the unit in the car. If the spacer was used, bleed the clutch hydraulics to compensate for the changed flywheel position.

RIC777JT Parts List

Ref No       Part No          Description                                          Qty/kit

1             3A0005          Seal housing                                             1

2             3A0006          Spacer                                                    1

3             NF641            Seal, 75mm x 100mm x 10mm, high speed      1

4             BF0405          Button head cap screw, 1/4-28 x .63              3

5             HF0508          Bolt, 5/16-24 x 1.00 , gr5                              3

6             HC0506          Bolt, 5/16-18 x .75 , gr5                               2

7             WL2051          Split lockwasher, 5/16                                5

8             WT2041          Toothed lockwasher                                     3