To return a motorcycle component (such as a frame) to its original “as new” condition often requires the use of a sand or grit blaster. No amount of cleaning, degreasing or sanding will return a component back to its original unpainted finish as quickly or easily as a grit blaster. However, there are some important rules to follow before grit blasting; otherwise, a component can be damaged beyond repair.
For this article we consider a classic motorcycle frame that needs to be repainted or powder coated.
Before disassembling, it is important to photograph the entire machine from every angle--this is particularly important where a workshop manual is not available. Photographs should be taken at every available opportunity as removal of the gas tank, for instance, will reveal wiring and cable routing positions.
When an item is grit blasted, the grit will of course get onto and into any unprotected areas. It is, therefore, essential to prepare the frame before subjecting it to grit blasting. This preparation should include the following:
Disassembly of Component Parts
When a frame is manufactured, all of the welding, grinding and machining work will have been completed. The frame tubes will be untreated (no paint, no primer, and no plating etc.) and in need of a degrease only before being painted. In the case of a frame subject to a restoration which includes grit blasting, the frame must be disassembled to the same specification as a newly manufactured item.
All brackets must be removed and any associated components--such as the swing-arm and stands.
Decals and tape (even the residue glue from below a piece of tape) will stop the grit from acting on the frame’s metal, and must, therefore, be completely removed.
To ensure the new paint will adhere to the frame, it is very important to thoroughly degrease all components. This degreasing must be done before grit blasting or grease will be forced into the surface of the metal which will result in a poor paint finish.
During the degreasing phase, the mechanic must wear protective (workshop safety) clothing including gloves. However, he or she should also wear protective gloves (latex, for example) when handling the frame after degreasing to avoid grease spots from forming where hands have touched the bare metal.
Regular hardware stores sell selections of rubber plugs. These plugs are ideal for sealing the head-stock bearing and swing-arm bearing locations. Any unsealed tubes should also be sealed to ensure that grit does not build up inside a frame rail, for instance.
Refit Bolts and/or Nuts
Wherever a component has been bolted to a frame, there will invariably be a mounting hole. Assuming the hardware will be replaced with new items, the old bolts should be replaced into their original location, this will help considerably when reassembling the bike and identifying the many bolts and nuts used.
Exposed threads, such as rear damper mounting studs, should be covered with plastic insulation tape to protect the threads during the blasting process.
It is critically important to grit blast motorcycle components carefully. If the owner is not doing the blasting work, he must inform the shop responsible that many of the components on a motorcycle can be damaged by too much grit or sand onto one area (it is possible to warp thin metal components). The grit blasting operator must also refrain from touching the bare frame with his hands at any time.
When the grit blasting is completed, it is very important to apply a coat of primer (assuming the frame is to be painted and not powder coated) to protect the bare metal.