The MGA With An Attitude

At 11:10 AM 10/21/99 -0800, Gregg Baker wrote:
>".... I checked the rockers and it's hard to tell if they're loose but I don't think so. I do have two that have scored the shaft pretty bad and will have to be replaced."

Rocker pedestals almost never wear out. Rocker shafts almost always need replacing, but it's a cheap part. Rocker arms sometimes need to be rebushed, but not always. Occasionally some very high mileage rockers will have pitted tips where they run against the valve stem. Those could be refaced in a machine shop, but generally not worth the expense. New ones are under $20 each. I can often buy a whole used rocker shaft assembly for $25 or less with all good rocker arms (bushings unknown).

The steel shaft wears more than the bronze bushing, because the soft bronze imbeds hard particles of "dirt" in the oil and uses that to abraid the shaft like sandpaper. Most of the wear is on the bottom of the shaft. Push the arm aside and run a finger along the bottom of the shaft, If you feel a ridge between a pair of grooves it's time to replace the shaft.

Consider the operating axis of the arm to run through the center of the bushing, and the long axis of the arm to be the line from tip to tip. Wiggle the arm by rotating it about the long axis to see if there is play in the bushing. If it looks sloppy, move the arm up the shaft a bit to a non-worn part of the shaft and try it again. If it has little or no play there that bushing is okay. If the arm still wobbles on a clean part of the shaft, then you need to replace the bushing.

>"Can I do this without special equipment and if so how?"

You may need a drill press to finish the job. Otherwise you can only do half yourself.

Start with a new bronze bushing in your hand. Select two socket wrench sockets to suit, one with the OD just a smidge smaller than the OD of the bushing, and the other just large enough for the OD of the bushing to slip inside of the socket. Place the rocker arm in a big vice with the two sockets positioned concentric with the old bushing, squeeze with the vice, and the bushing will be pushed out with the smaller socket into the barrel of the larger socket.

Putting the new one in is even easier, just line it up with the bore of the rocker and squeeze them together with the vise. If the vice has textured jaws it would be a good idea to place something hard and smooth between the bronze bushing and the vice jaw to avoid maring the end of the bushing.

Next, you need to remove the drive rivet used to plug a hole in the end of the arm carrying the adjuster screw. Start by removing the adjuster screw, then grind off the head of the rivet, then use a pin punch to drive the shank of the rivet through into the threaded hole.

Next step is to drill two small holes through the new bushing for oil flow. One hole comes out the top of the rocker arm at an angle to throw oil in the general direction of the valve stem contact point. The other hole goes through the adjuster end of the arm to supply oil to the adjuster screw to lube the top end of the pushrod. Select the small drill bits that just fit through the existing holes in the forged arm, use the existing holes like drill bushings, and drill the new holes through the bronze bushing. If you're careful you can do this with a hand drill.

Then the new bushing has to be reamed through to provide the running fit on the rocker shaft. For this use a common 5/8" chucking reamer (usually having a 1/2" shank). This tool should be under $25 at any industrial machine tool supply vendor. In this case the bore of the bushing is about as large as the length, so the reamer will not self guide, and the rocker arm needs to be set up in a drill press with a vice to hold it for reaming. A single pass with the reamer with a slow speed, lots of oil, and a moderate feed rate makes the bore of the bushing exactly 0.6250" diameter. The rocker shaft is 0.001-0.002 undersize, so the rocker arm should then be a nice working slip fit on the shaft.

The last task is to plug the hole in the adjuster end of the arm. For this I use a #4-40 binding head machine screw. The screw can be cut to the right length (short) with the screw cutter usually included in a wire terminal crimping pliers. The #4 screw needs to be short enough not to interfere with the threads of the adjuster screw. Just align the #4 screw with long nose pliers and tap it into place with a tack hammer. The threads of the screw will deform a little and it will jam in the hole just like the original drive rivet. Also wouldn't hurt to put a drop of Loctite 242 adhesive on that screw before you drive it into place, just to be sure about being secure.

Note: The forged rocker arm is very hard. Do not attempt to tap a thread into it, or to drill the small holes out any larger. This is futile and only results in burned drill bits and broken taps. Otherwise, have fun with the project. Also note that some late production MGB rocker arms may not have the small drilled hole leading to the adjuster screw at the pushrod end of the arm.

Then at 08:36 PM 3/21/03 -0500, Doug Sjostrom wrote:
>"I'm wondering why people don't pre-drill the bushings before pressing in order to avoid the hassle of plugging the oil hole again. Although you have to watch the alignment during installation, seems as if a larger hole could be tolerated without adverse consequences, ...."

That sounds like a very good idea. Most of the mechanical load in the bushing is at the bottom when it bears heavily upward against the shaft. I'm sure a slightly larger hole in the side wouldn't affect anything functionally. If you didn't get it straight the first time you could still remove the bushing and try again. It should be easy enough to position the hole when drilling, being straight radially and dead on center of the bushing.

The hole on top would be a harder to align and to predrill at an angle without a special drill jig, so better to drill that one after installation anyway.

One more foot note here. New replacement rocker arms may not have the drilled hole to supply oil to the adjuster screw. Arms without this hole are the later MGB spec parts. It seems that for the MGB the early part is superceded by the later part, as someone at the factory apparently decided that lubrication on that end of the arm was not necessary. I rather prefer to use arms with the drilled oil hole for the adjuster end, but maybe it's just a matter of suspicion.

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