Appendix B     Assessment of Corrosion The effect of corrosion on the safety of a motorcycle is a difficult matter to resolve since it depends not only on the extent of the corrosion but also on the function of the section in which it has occurred. A small amount of corrosion which substantially weakens an important component or part of the structure would render the machine unsafe, whilst significant corrosion of a less important part may be acceptable. Where corrosion is present the tester must make an assessment of its severity and identify whether it is in a load bearing member or a highly stressed part such as a frame or suspension component, reaction bracket etc. The extent of the corrosion should be determined by pressing hard with finger and thumb. If necessary careful scraping and light tapping of the affected areas with the Corrosion Assessment Tool is permitted. Sharp instruments or heavy blows must not be used. Excessively corroded metal or metal treated with filler (which may camouflage corrosion) emits a duller sound than uncorroded metal. Having determined the extent of the corrosion the tester must use his experience in judging whether the degree or position of the corrosion has significantly affected the strength of the part having regard to the amount of sound metal remaining. A further criterion which may be applied in judging a part which is excessively corroded is whether it is likely to make the machine dangerous to use on the road under any condition of use including fast cornering, emergency braking etc. If the tester considers the machine would be safe to use the component should not be regarded as defective: however the tester should advise the owner of the presence and location of this corrosion. On the other hand if the strength of certain parts is very seriously reduced by corrosion the tester may refuse to carry out a brake test.   (Ref:  Introduction: Item 2). Where a corroded part has been repaired it is essential that this has been carried out using suitable materials and techniques so that it is virtually as strong as the original part. Repairs to load bearing members or sections by pop riveting or glass fibre are not acceptable, but in some cases these methods may be used for repairs to non load bearing parts. Welded repairs to highly stressed components such as suspension arms etc are not normally acceptable. If in doubt consult the vehicle or component manufacturer.    Brazing, soldering, glass fibre and body filler are bonding processes; they are not regarded as strong enough for repairs to load bearing members although they are normally adequate for other repair work. Brazing, bonding and riveting are only acceptable where used by the vehicle manufacturer and the standard of any such repair must be comparable to the original. It is sometimes difficult to distinguish between welding and brazing after the repair has been covered in paint or underseal. However, brazing may be detected by the smooth fillet of filler or a gold colouration at the edge of a joint. Glass fibre, body filler, aluminium etc may often be detected by a difference in appearance, in sound when tapped, or by the use of a magnet. The Motor Bicycle and Side Car M.O.T. Inspection Manual   Issue Date 10 January 2005