How To: Make Timing Gear Bushings
I’ve had so much free time lately, I pulled the motor open in the Premier to check things over before the long ride. There was a bit of aluminum swarf in the bottom of the timing chest, inspection showed that two of the timing gears had been rubbing on the inner timing case. Then with the cover off, one bushing fell out of the hole that it was supposed to be pressed into. So it was time to make some new bushings…
Measuring the bushings. Too large on the id.
One bushing fell out of the case, but the others were still held tight. So I used the old trick of popping them out by pushing in a dowel pin. This works if the bushings have a through hole, and are mounted in a blind hole in the case. Step 1. Fill the bushing bore with grease.
Step 2. place a dowel pin or drift into the bore. This should be a sliding fit.
Step 3. Hit the end of the dowel. The grease is an incompressible fluid, it has nowhere to go. So it pushes up on the back of the bushing. That pops the bushing up out of the housing. For long bushings, you might have to stop and put in more grease, then hit the pin a second time to get the bushing all the way up and out.
Lots of standard bushings are available from the typical sources like MSC, McMaster Carr, Anchor Bronze, etc. The dimensions on the Premier were not quite the same as the off the shelf bushings, so I made them from scratch. This bar is SAE 841 oil impregnated sintered bronze, about $15 or $20 for 6” length from McMaster. The material is porous, and filled with oil. When the motor is running, the spinning shaft heats up, some of the oil comes out of the bronze to lubricate the bearing surface. When it cools, it goes back in. This material works very well for early motors that have minimal lubrication systems. It is also easy to cut on the lathe, as it self-lubricates during cutting.
Facing the bushing to the correct thickness.
Milling the notch that clocks the bush in the cases.
The bushings were lightly pressed into the outer timing case. Small steel pins are in the case, they contact the notch cut in the bearing to stop it from rotating. A small groove was cut into the face of each bushing flange to allow oil to run down onto the gear shaft. When this timing cover is installed, each of the oil grooves is oriented vertically.
After the first bush was installed, the ID was checked against the gear shaft. If it was tight due to the interference with the cases, the bush was popped back out for a very light cut on the ID. Final sizing was about .0015” to .002” over the shaft diameter, with about .010” end float between the two bushings that support each gear (one on the inner case and one on the outer). As the motor heats up, the aluminum will expand more than the steel gears, which will give slightly more clearance on both the diameter and end float.
Gratuitous shot of the cast iron piston. Wide rings, with bevel cuts. Note that the top ring groove has two rings in it. Also note that there are no oil rings (constant loss oil system).
Here you can see the ball that rides on the cam lobe. It is a very interesting design, I do not know of any other motor that uses balls for cam followers.
So many parts in this valve train… From the top:
Valve and guide
Adjuster and tappet
Tappet guide (on the left)
2 piece Lifter and compression spring
Ball cam follower
Cam, shaft and gear.