Rebushing Sloppy Solex Throttle Shafts
Aug 24, 2015 15:47:14 GMT -5
Post by vanapplebomb on Aug 24, 2015 15:47:14 GMT -5
Just figured I would share this with you guys in case you ever wanted to fix up your sloppy and leaky Solex throttle shafts.
There were a few reasons that the throttle shafts went sloppy on the Solex carbs. Bushings wore out due to their small load bearing area relative to their PV rating, and lack of lubrication. Throttle shafts pitted and coroeded away from galvanic corrosion, aka, the steel shaft is more anodic than the bronze bushings.
The solution is to minimize bushing wear by increasing the load bearing area, keeping the PV rating (pressure*velocity, a standard unit of measure for a bearings resilience to the effects of pressure and velocity) up to a suitable level, and providing better lubrication.
Bushing wear is only just half the picture. Galvanic corrosion needs to be minimised. This means that the steel throttle shaft can not be in contact with any material significantly more cathodic or anodic than itself. Steel is much more anodic than the bronze bushings, which is why the throttle shafts were eaten away so badly where they contacted the bronze. Unfortunately there are so suitable metallic bearing materials that approximate steel in the galvanic series that would minimize corrosion in the absence of lubrication.
My solution to get around these problems present in the factory carbs is to use larger polymer composit dry run bearings. I selected the igus iglide T500 bearings. Their sturdy fiber reinforced construction makes them as tough as sintered bronze. Solid lubricants provide excellent dry lubrication for the pivoting motion of the throttle shaft, which is something bronze or oil impregnated sintered bronze is poor at. The lack of electrical conduction minimizes damage due to galvanic corrosion. Resistance to heat and solvents was also a factor.
The size of the bearing is 5/16"id, 3/8"od, and 1/2"long. Stock throttle shafts were 8mm from the factory. Due to galvanic corrosion, most are now undersized at the bushings, this why I chose 5/16in bushings. They are ever so slightly undersized. Throttle shafts are easily resized by chucking them up in a drill press or lathe and sanding them down to size.
The aluminum throttle bodies are soft and drill like butter. A good sharp 3/8in drill bit and cutting fluid is all you need. drill each end to a depth of 1/2". A simple jig to line things up for straight collinear drillings is strongly advised.carefully press in the bearings. Using a pilot such as a 5/16" drill bit works great to keep the bearings strait as they are pressed in. Once they are in, chuck up the throttle shaft and size them down as described above until they fit nice in the new bearings without binding.
You should note that the two flathead screws holding the throttle plates on are peened over on the back side to keep them from loosening. You must grind this off before trying to remove the screws. If you don't, you will damage the threads if you are lucky, or the head will snap off, and then your screwed. When you reinstall the throttle plates, just use fresh screws and secure them with Loctite 271. I tested this on a spare throttle shat to see if it was strong enough. It is. The head snapped clean off the threads. It also was resistant to soaking in acetone for a few hours. If that isn't good enough for you, I don't know what is. Hahah
There were a few reasons that the throttle shafts went sloppy on the Solex carbs. Bushings wore out due to their small load bearing area relative to their PV rating, and lack of lubrication. Throttle shafts pitted and coroeded away from galvanic corrosion, aka, the steel shaft is more anodic than the bronze bushings.
The solution is to minimize bushing wear by increasing the load bearing area, keeping the PV rating (pressure*velocity, a standard unit of measure for a bearings resilience to the effects of pressure and velocity) up to a suitable level, and providing better lubrication.
Bushing wear is only just half the picture. Galvanic corrosion needs to be minimised. This means that the steel throttle shaft can not be in contact with any material significantly more cathodic or anodic than itself. Steel is much more anodic than the bronze bushings, which is why the throttle shafts were eaten away so badly where they contacted the bronze. Unfortunately there are so suitable metallic bearing materials that approximate steel in the galvanic series that would minimize corrosion in the absence of lubrication.
My solution to get around these problems present in the factory carbs is to use larger polymer composit dry run bearings. I selected the igus iglide T500 bearings. Their sturdy fiber reinforced construction makes them as tough as sintered bronze. Solid lubricants provide excellent dry lubrication for the pivoting motion of the throttle shaft, which is something bronze or oil impregnated sintered bronze is poor at. The lack of electrical conduction minimizes damage due to galvanic corrosion. Resistance to heat and solvents was also a factor.
The size of the bearing is 5/16"id, 3/8"od, and 1/2"long. Stock throttle shafts were 8mm from the factory. Due to galvanic corrosion, most are now undersized at the bushings, this why I chose 5/16in bushings. They are ever so slightly undersized. Throttle shafts are easily resized by chucking them up in a drill press or lathe and sanding them down to size.
The aluminum throttle bodies are soft and drill like butter. A good sharp 3/8in drill bit and cutting fluid is all you need. drill each end to a depth of 1/2". A simple jig to line things up for straight collinear drillings is strongly advised.carefully press in the bearings. Using a pilot such as a 5/16" drill bit works great to keep the bearings strait as they are pressed in. Once they are in, chuck up the throttle shaft and size them down as described above until they fit nice in the new bearings without binding.
You should note that the two flathead screws holding the throttle plates on are peened over on the back side to keep them from loosening. You must grind this off before trying to remove the screws. If you don't, you will damage the threads if you are lucky, or the head will snap off, and then your screwed. When you reinstall the throttle plates, just use fresh screws and secure them with Loctite 271. I tested this on a spare throttle shat to see if it was strong enough. It is. The head snapped clean off the threads. It also was resistant to soaking in acetone for a few hours. If that isn't good enough for you, I don't know what is. Hahah
