MG TC 1187 Bishop Cam Steering Gear Renovation

Introduction

In 1998, I was sent to South Africa to oversee installation and commissioning of an ozone generation system at the Wiggins Water Treatment Works for Umgeni Water in Durban. A colleague of mine, Nick Purcell, who worked for Umgeni Water, knew I was interested in classic MGs and found TC1187 advertised in the small adds section of a local Durban newspaper.

I imported the car from South Africa in late 1999.

Since then it has sat patiently in my garage waiting for me to start the restoration. Little did I know that it would be 17 years before I would start the work.

The steering was an issue from the start with a pair of grips in place of a steering wheel and the only way to move the car around was by disconnecting the drag link and manually moving the wheels.

Having finished the restoration of my MGB GT and started work on my MGB V8, I needed more space in the garage. Rather than relegate the TC to an outside spot with a cover, I decided to get the steering working so I could move it out of the way when working on the V8 and back inside when I was not.

The problem with this approach was as soon as I started working on the TC steering the bug bit and the restoration of the V8 is now on the back burner.

The job split down into the following stages of work and I describe each in turn with plenty of photos to help:

• Removal of steering gear from the car

• Dismantling

• Listing parts required

• Pre-assembly

• Machining

• Final Assembly

Remove the steering gear from the car

The steering box assembly was removed from the car by undoing the steering column clamp, disconnecting the drop arm and undoing the steering box mounting bolts. The assembly was then removed by sliding the steering column forward and out of the car under the splash apron.

Dismantling

Once on the bench the bottom and side covers were removed and ball bearings rained out as the cage bearings were very badly damaged (see pictures). On inspection, it was obvious that the problem was not due to wear and tear, but due to incorrect assembly and missing components like the bottom bearing cup had been left out.

The box was filled with grease rather than oil, and no gaskets were installed.

The steering column spline was badly worn and holes had been drilled through column to fix the steering wheel as the splines on the steering wheel had been damaged.

Steering column had also been damaged where it is inserted in to the Bishops cam as can be seen in the picture above.

Listing Parts Required

It was obvious that the steering box required a total rebuild and that the steering column required replacing.

I was able to purchase a new spline fitting steering column and most all other parts needed for the rebuild of the Bishops cam steering box except for the cage bearings which proved to be elusive. I placed then on back order with several well-known suppliers and waited. In fact, it took nearly a year before they became available and four turned up within a couple of days from different suppliers.

Since I bought the car I have been building up a stock of spare parts for the renovation, including various bits for the steering and a Tompkins kit which I bought in 2002. Parts purchased for the steering rebuild include the following:-

Pre-Assembly

Once all the parts became available I degreased and cleaned the box and fitted all the components in a dummy run to check that everything would fit prior to final assembly.

The Tompkins kit components were checked as it was purchased back in 2002 and some were found to be rather rusty which needed attention. The sector shaft and the Tompkins kit thrust bearing and spacers were checked for compatibility and from the installation instructions it was seen that the sector shaft required machining to provide a perfectly flat surface for the thrust bearing (next two photos).

It was my intention to press out the sector shaft peg, turn it 90^o and press it back in so it presented a fresh unworn surface to the cam gear however as a new peg was around £15.00 I decided to replace it.

Play was also detected on the sector shaft when installed in the steering box which required a new bush to be installed and reamed. Prior to reaming, the sector shaft needed surfacing to remove scratches and damage caused by incorrect installation of the cage bearings. The bush was not currently available and it require a machine shop to manufacture install and ream as required (pic below).

On close inspection, it was seen that the steering box upper bearing retainer required machining to repair damage caused by incorrect installation of the upper bearing cup where it had been forced in to the casing on the skew, probably when force was applied to the column in an attempt to turn the wheel. The bearing face needed to be machined flat and the rim de-burred to allow the new bearing cup to be installed (pics below).

Machining

Machining needed to be done to prepare the box for re assembly which included the following:

-Machine sector shaft top to present a flat surface to the Tomkins needle roller bearing

-Resurface the sector shaft

-Install a new peg in the sector shaft

-Install and ream a new bush for the sector shaft

-Machine the bush to allow for cam gear installation

-De-burr the upper bearing cup retainer and thrust surface.

The estimated cost was between £100.00 to £110.00 however during the work it was found that the housing at the top of the sector bush bore was distorted which required a special bush to be made this increased the cost to £126.00.

Before taking the steering box to be machined a first coat of enamel was applied to protect the stripped de-rusted and de-greased surfaces.

While preparing the steering box I found a sleeve inside the column; it is about 200 mm long and a tight fit, there is a hole through the wall of on side at one end of the tube. As I could not find it in any exploded views I believe it may have been a part of previous attempt to repair the steering and I decided to leave it out.

Final Assembly

One final check on all the parts before re- assembly. This confirmed that I have all parts needed. But I noticed that the circlip groove was missing from the new steering column. My lathe is not big enough to add this so back to the machine shop.

During pre assembly I noticed that the sector shaft bush was not protruding as it should to allow the seal to seat correctly. To correct this I machined a spacer from the old bush to install on the sector shaft to effectively make the bush 3 mm longer which will allow the seal to seat on to the bush. (See Ed’s note at end of article).

Next stage was to install the top bearing cup in the casing.

The top cage bearing, the Bishops cam, the bottom cage bearing and the bearing cup came next. As new bearing cups and cages had been installed the existing thickness of the shims was not relevant. I installed the end plate and gently tightened until no lateral play was detected on the steering shaft and importantly that it was not pre- loaded.

The gap was measured using feeler gauges and shims of that thickness were installed between the casting and the bottom plate.

Installing the Tompkins kit came next. The needle bearing and washers fouled the casing and a small amount of grinding of the casing was required to ensure that the adjuster could move freely. To do this I had to remove the bearings, sector shaft and cam and after grinding away the offending metal carefully wash away any residue from the casing.

After modifying the casing the Tompkins kit fitted without any problems and the adjuster was loosely tightened to hold everything in place. The column anti rattle bush, needle roller bearing and shim that came with the Tompkins kit were installed. I fitted the drop arm loosely to hold the oil seal in position.

I added a small amount of Penrite Trans 140 through the “grease” nipple to ensure that everything within the box was covered with a protecting layer of oil. It will be filled to the correct level after it is installed in the car. The steering system is now ready for installation in the car once the body has been restored.

Paul Rutherford

Ed’s note: Thank you for this article, Paul.

Regarding the fitting of the oil seal it is more usual to counterbore the housing to fit it. The following picture from Eric Worpe’s article in Issue 26 of TTT 2 illustrates this:

With regard to the Tompkins kit, I feel it is important to reproduce Eric’s comments from the same article mentioned above, as follows:

Some modified top-plates are available that set the peg’s mesh by use of a thrust bearing that’s positioned using a threaded adjuster in line with the sector shaft. This produces a bending moment on the sector arm which has resulted in fractured arms.

If you have such a modified top-plate and find that the box has started to need frequent adjustment to reduce play, DO NOT delay replacing the sector shaft with a modern steel alloy replacement. Even if there are no signs of a fracture and you chose to continue using a modified top-plate, then at least consider replacing the old sector shaft before any signs of a fracture or of twisted splines occurs.