The pilot bushing is an “oil impregnated bronze bushing” located in the back of the crankshaft. Its function is to keep the transmission first motion shaft (input shaft) in alignment with the centerline of the crankshaft. It is normally inspected when the clutch is being replaced. It is normally replaced as part of an engine rebuild. It may, however, be desirable to replace the pilot bushing when only replacing the clutch if you do not know the history of the bushing (how many years has it been in service), or if you find the bushing loose in the end of the crankshaft, or if the inside of the bushing is scored or grooved. Simply cleaning the interior of the bushing and running a finger inside it will tell you if there has been scoring or grooving inside the bushing. Trying to remove it with the finger will tell you if it is loose enough to fall out. I have seen both over the years. Under any of these conditions, you may decide to replace the pilot bushing. This article should tell you how to do so.
There are three basic sizes of pilot bushings used in the MGB. The Mark I cars used one with a smaller internal hole than the Mark II onwards cars because the input shaft of the three syncro gearboxes was smaller. The inside hole of the pilot bushing, when fitted to the crankshaft, is about .002” to .005” larger than the outside diameter of the first motion shaft. Each strand of hair on your head will measure about .002” or slightly larger.
On the Mark II and later cars, the same basic bushing was used. On the “G” series cars, this bushing was 1 ½” long. On the 18V engines, the length of the bushing was reduced to about 1”. The longer bushing cannot be used with the 18V crankshafts, but several people have reported fitting the shorter pilot bushing to the earlier engines. Ideally, however, you should use the longer bushing with the earlier crankshafts.
Pilot bushings should be soaked in engine oil for about 24 hours before being installed. I use a small pill bottle with a tight fitting cap to soak my bushings. Prior to installation, wipe the bushing dry. The oil should have soaked into the bronze of the bushing.
There are special pilot bushing removal tools available. These can, sometimes, be rented from tool suppliers. Some auto parts stores have these tools available for use without cost. (You do, however, have to leave a significant deposit, returned when the tool is returned in good condition.)
Since the special tools are not always available, nor are they always available when you need them, hobbyists have developed an alternate method of removing the pilot bushing. One which works quite well.
The first step is to make sure the engine or crankshaft is securely supported. I like to have the engine sitting on a small bench at about waist height. The rear of the crankshaft is cleaned thoroughly then, the opening in the pilot bushing and the area behind it is filled with thick grease. Use the heaviest grease you can find. Axle grease seems to work fine, but the older style grease, which was much thicker, worked better.
When the interior cavity is fully packed with grease, insert a tight fitting punch, put a rag around the area to keep the grease from splattering, hold the punch in one hand and strike the other end with a heavy hammer using medium force. (Note, you may have to remove the punch and insert more grease as the grease is compacted.) A heavy hammer, swung with medium force is both more effective and more easily controlled than a light hammer striking a heavy blow. You want a hammer somewhat heavier than the type normally used for removing and replacing the center spinners of wire wheels. I use a small “hand sledge hammer” for driving the bushings in and out.
With several blows, the grease will be forced inwards into the crankshaft cavity, forcing the pilot bushing out. The initial blows of the hammer may cause the drift to displace air pockets which were not filled with grease. In this case, remove the drift, pack in some more grease and begin again. Eventually, the pilot bushing will be pushed free of the crankshaft recess. Remove the loose pilot bushing, clean the interior cavity well then, get ready to insert the new bushing.
Wipe off all of the excess oil from the bushing. I then use an aluminum collar, slipped over the end of the drift, to drive the bushing back into the cavity in the crankshaft. This allows the punch to drive the bushing all the way back against the stop ridge in the crankshaft on the 18V engines. Not all of the earlier engines have this ridge. You can also use a small block of hard wood against the rear face of the bushing and tap the bushing into place by hammer blows to the wood. This leaves the bushing standing slightly higher then it should be and you have to gently try to tap it fully home without damaging the rear end. A properly sized (outside size) socket can be used to do this, normally, without any damage to the bushing.
After the bushing is installed, run your finger around the inner, rear edge(by this I mean the rear edge in relation to the engine—the portion visible to you after the bushing is installed and make sure no burrs have been raised. There should not have been. If any burrs have been raised, remove them with a fine, circular needle file. At that point, you are finished and ready to either install the flywheel or install the clutch to the flywheel. If you had removed the flywheel for resurfacing, clean the holes for the flywheel bolts with a good organic solvent, clean the bolt threads install the bolts using a drop of blue, medium strength, Loc-Tite on each bolt and use a new locking tab for the bolts. I have seen old, re-used locking tabs break, allowing the flywheel bolts to back outwards. Thus, the “belt and suspenders” approach works best.
There are a few times when the grease and drift method do not work. Usually, this is when a Dreaded Previous Owner has secured the bushing into the crankshaft using some form of chemical bonding compound. If the bushing does not come out due to the hydraulic force of the grease, the next step is to use a pilot bushing removal tool. This may, or may not, work. If the pilot bushing cannot be removed by ordinary means, it must be removed by extraordinary means—lathe turning.
In lathe turning, the crankshaft must be removed from the engine and mounted in a lathe. The front end of the crankshaft goes into the headstock chuck of the lathe and the rear end is supported by a three position steady rest. A boring bar, preferably made of high speed steel rather than carbide, is then used to bore out the old bushing, leaving the interior surface of the crankshaft undamaged. This, however, is so unusual that I have never seen it required and have only read about it once. All of the pilot bushings I have had to remove over the years have come out, easily, with the grease and drift method.
This monograph may be reproduced only for non-commercial use without other permission of the author. Reproduction for commercial use only by written permission.
Copyright © 2004 by Les Bengtson