Tech Tip – Spring 1994

TR3 Cam Replacement
Randall Gill, Clearwater, FL

Recently, I had to change the camshaft in my TR3 due to a damaged fuel pump lobe. Engine otherwise in excellent condition (head, valves, etc.). I found a way to change the camshaft without the cost and labor of pulling the cylinder head.

Remove the rocker arm shaft and push rods and place eight magnets secured to pieces of wire hanger down each push rod rube. Gently lift each tappet, being sure not to lift too far, as they may fall over into the space below the head. Two tappets can be felt by reaching in through fuel pump mount opening. This is the easiest way to determine the amount of lift needed. When all tappet arc raised that amount, the cam can be replaced following normal procedures. When the new cam is in place, hold each tappet down using a wooden dowel and remove the magnet.

MGB Manifold Leak
Wolf Campbell, Houston, TX

Every time I work on my Z-S carb I discover new revelations about its simplicity and operating principles. This time after installing a re-worked cylinder head on my ’77 MGB, I learned the hard way that the key to proper operation of this carb is vacuum: nothing works without vacuum. Anything that interrupts or corrupts the vacuum developed by the engine translates into poor or non-existent operation.

My problem stemmed from not exercising care when installing the intake/exhaust manifold. In my haste I allowed the manifold to hang on the manifold studs while tightening the nuts. Since the manifold slots are very much larger than the studs, this provided a gross vacuum leak that leaves one inopportunity stranded. Symptoms were that the engine would start after excessive cranking, but would not idle. Revving caused sluggish acceleration accompanied by sputtering and spitting.

If this sounds familiar, get the wrenches out and a new manifold gasket (Moss Motors #297-530). Instead of allowing the manifold to hang on the studs, install a temporary spacer, tube, or deep well socket over the studs at the front and rear of the engine. These spacers will center the manifold while the central manifold nuts are snugged down enough to hold the manifold in place.

About Wire Wheels
Lawrie Alexander, Shingle Springs, CA

One of the less popular aspects of wire wheels is that they tend to go ‘out of tune’ and need occasional straightening (or ‘truing’). This is caused by the spokes stretching and by the spoke holes wearing, both of which result in a change in spoke tension. This causes the rim to run out-of-round.

Consider that the weight of the car is suspended on the few spokes that are uppermost in each wheel and that they are constantly moving into and out of this weight-bearing position when the car is moving. Add side loads from cornering and you can understand the stresses that cause the spokes to stretch and move around.

A wheel which is tuned to run true may be kept this way by monthly checking of spoke tension. Run a pencil around the spokes and note whether any make a sound which is markedly lower in pitch than the others. Tighten these ‘Hat’ ones with a Moss spoke wrench (#385-800) and you will maintain the wheel in a nice, round condition.

Old Wheels

If your wheels have not been trued for some time, simply tightening the ‘flat’ spokes will not necessarily make them run true. You might just tighten them permanently into their buckled condition! An old wheel should be properly trued to eliminate radial and lateral run out before being put on the monthly maintenance program.

New Wheels

When the wheels arc assembled at the factory, they are laced so as to be within factory tolerance for radial and lateral run out. Since the hubs, rims, and spokes are new, this tolerance can be achieved without the spokes necessarily being tensioned evenly! Result? When a new wheel is subjected to a load, it may go slightly out of round. Even when the spoke tension is correct, some settling will occur during the first couple of hundred miles, as the spokes and nipples bed into their scats. A good practice with new wheels, therefore, is:

A) Check spoke tension before mounting new tires. Tighten any loose spokes, check for excessive run out and remedy by tightening appropriate spokes.

B) Drive gently on new wheels at first, allowing them to settle in without severe stress.

C) Re-check spoke tension and run out after new wheels have been used for a couple of hundred miles or so.

Following this procedure, and remembering to clean and re-grease the hub splines every 4-6 months,
will give you years of trouble free life from your wire wheels.