Maxi Bush
In August 2001 my Maxi failed it’s MOT due to defective Rear Radius Arm Bushes. I tried fitting two non standard ones but they soon collapsed. Because the original “Metalistic” bushes were hard to find I decided to design my own. I originally thought of a design using sealed roller bearings and an internal spring to mimic the torque of the rubber. However investigation soon revealed that there were no suitably sized bearings for the job. After a great deal of thought I came up with the following simple design.
I've fitted 2 bearings based on this design to my Maxi and so far have travelled many miles without any problems. The design above involves replacing the rubber in the original bush by a mild steel block with plain polymer bearings pressed into the centre from both ends. (The rubber can be drilled out but I find placing the original bush in a small fire at the top of the garden works better) The mild steel block is machined to interference fit into the machined-out outer part of the bush then locked in place with two high tensile bolts. A new internal shaft is machined to fit the polymer bearings with a flange on the inner end to prevent outward movement of the radius arm. (The internal diameter of the polymer bearing is 35 mm whilst the original shaft has an outer diameter of 34 mm) The outer end is machined to mimic the end of the original shaft (34 mm) so the washer will fit as it should.
A later - improved - design of mine is similar except that the two polymer bearings have flanges to prevent movement. The inner shaft has it’s flange the same width as the flange on the bearing. These flange surfaces should help to prolong the life of the bearing. One final note - before pressing in the polymer bearings the unit is pained.
The modern polymer bearing is self lubricating and needs no additional lubrication. It fits a wide spectrum of applications and if development continues as I expect then it will eventually replace the traditional ball and roller bearing. I selected a bearing most suited to this particular application - type W300 - item number WFM-3539-16. It's self lubricating, works well in a wet abrasive environments and has shock absorbing properties. The company that supplied me with the bearings is called Igus.
You can expect to pay about £5.00 per bearing and you’ll need two per bush. Machining will cost about £65.00 per bush. Both sides of the car should be replaced at the same time. The diagram and description are only suggestions. If anyone wishes to reproduce their own bushes for their own use they do so at their own risk.
The modern polymer bearing is self lubricating and needs no additional lubrication. It fits a wide spectrum of applications and if development continues as I expect then it will eventually replace the traditional ball and roller bearing. I selected a bearing most suited to this particular application - type W300 - item number WFM-3539-16. It's self lubricating, works well in a wet abrasive environments and has shock absorbing properties. The company that supplied me with the bearings is called Igus.
You can expect to pay about £5.00 per bearing and you’ll need two per bush. Machining will cost about £65.00 per bush. Both sides of the car should be replaced at the same time. The diagram and description are only suggestions. If anyone wishes to reproduce their own bushes for their own use they do so at their own risk.
I have found that the bearing tends to “grunt” on occasions....... a dose of WD40 or similar curtails the problem. This problem was later identified with the mark 1 bush which has no flange on the polymer bearing. This causes metal to metal contact of the inner end.
If I were to modify the bearing in any way I'd extend the inner shaft flange out beyond the polymer bearing flange and machine a groove in the block to take an O ring (repeated on the other side) ....... in order to help keep water out. I might even go one further and use an oil seal ring! I’m sure two rubber O rings could be suitably squashed underneath the outer cap washer to prevent ingress of water etc. without having to machine a groove.
If I were to modify the bearing in any way I'd extend the inner shaft flange out beyond the polymer bearing flange and machine a groove in the block to take an O ring (repeated on the other side) ....... in order to help keep water out. I might even go one further and use an oil seal ring! I’m sure two rubber O rings could be suitably squashed underneath the outer cap washer to prevent ingress of water etc. without having to machine a groove.
New polymer bearing bush with original BL Rear Radius Arm Bush
(Part Number 21H406)
(Part Number 21H406)
I have shown the new bush to Dr. Moulton and he has given it the thumbs up.
REDESIGNED RADIUS ARM BUSH
